1.
Gray code
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The reflected binary code, also known as Gray code after Frank Gray, is a binary numeral system where two successive values differ in only one bit. The reflected binary code was designed to prevent spurious output from electromechanical switches. Today, Gray codes are used to facilitate error correction in digital communications such as digital terrestrial television. Bell Labs researcher Frank Gray introduced the term reflected binary code in his 1947 patent application and he derived the name from the fact that it may be built up from the conventional binary code by a sort of reflection process. The code was named after Gray by others who used it. Two different 1953 patent applications use Gray code as a name for the reflected binary code, one of those also lists minimum error code. A1954 patent application refers to the Bell Telephone Gray code, many devices indicate position by closing and opening switches. In the transition between the two shown above, all three switches change state. In the brief period while all are changing, the switches will read some spurious position, even without keybounce, the transition might look like 011 —001 —101 —100. When the switches appear to be in position 001, the observer cannot tell if that is the real position 001, if the output feeds into a sequential system, possibly via combinational logic, then the sequential system may store a false value. This is called the property of a Gray code. In the standard Gray coding the least significant bit follows a pattern of 2 on,2 off, the next digit a pattern of 4 on,4 off. These codes are known as single-distance codes, reflecting the Hamming distance of 1 between adjacent codes. Reflected binary codes were applied to mathematical puzzles before they became known to engineers, martin Gardner wrote a popular account of the Gray code in his August 1972 Mathematical Games column in Scientific American. The French engineer Émile Baudot used Gray codes in telegraphy in 1878 and he received the French Legion of Honor medal for his work. The Gray code is attributed, incorrectly, to Elisha Gray. The method and apparatus were patented in 1953 and the name of Gray stuck to the codes. The PCM tube apparatus that Gray patented was made by Raymond W. Sears of Bell Labs, working with Gray and William M. Goodall, Gray codes are used in position encoders, in preference to straightforward binary encoding
2.
Shades of gray
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Variations of gray or grey include achromatic grayscale shades, which lie exactly between white and black, and nearby colors with low colorfulness. A selection of a number of various colors is shown below. Below is a showing the computer web color grays. An achromatic gray is a color in which the red, green. The web colors gray, gainsboro, light gray, dark gray, a chromatic gray is a gray color in which the red, green, and blue codes are not exactly equal, but are close to each other, which is what makes it a shade of gray. The colors white and black are not usually thought of as shades of gray, since achromatic colors have no hue, the hue code is left blank for achromatic colors. A white visual stimulation will be void of hue and grayness, white is the lightest possible color. Black is the color of objects that do not emit or reflect light in any part of the visible spectrum, black is the darkest possible color. Achromatic grays are colors in which the rgb values are exactly equal, since achromatic grays have no hue, the hue code is indicated with a dash. Achromatic grays are the axis of the sphere, with white at the north pole. The various tones of gray are along the axis of the color sphere from white at the top of the axis to black at the bottom of the axis. At right is displayed the web color gainsboro, gainsboro is a pale tone of gray. There is no evidence the name gainsboro was used as a name before it was included as one of the X11 colors when they were formulated in 1987. At right is displayed the web color light gray, displayed at right is the web color silver. This color is a representation of the color of the metal silver This is supposed to be a color, however. At right is displayed the color gray, or gray in the X11 color names. The coordinates in the X11 were set at 190 to avoid gray being displayed as white on 2-bit grayscale displays, see the chart Color names that clash between X11 and HTML/CSS in the X11 color names article to see those colors which are different in HTML/CSS and X11. At right is displayed the dark medium gray, or dark gray in the X11 color names
3.
Color depth
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For consumer video standards, such as High Efficiency Video Coding, the bit depth specifies the number of bits used for each color component. When referring to a pixel the concept can be defined as bits per pixel, which specifies the number of bits used. When referring to a component the concept can be defined as bits per component, bits per channel, bits per color. Color depth is one aspect of color representation, expressing how finely levels of color can be expressed. The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a code value to a location in a color space. Comparison, same image on five different color depths, different looks, but also different file sizes. With the relatively low color depth, the value is typically a number representing the index into a color map or palette. The colors available in the palette itself may be fixed by the hardware or modifiable within the limits of the hardware, modifiable palettes are sometimes referred to as pseudocolor palettes. 1-bit color, monochrome, often black and white, compact Macintoshes, 2-bit color, CGA, gray-scale early NeXTstation, color Macintoshes, Atari ST. 12-bit color, some Silicon Graphics systems, Color NeXTstation systems, for example, in the ZX Spectrum, the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8x8 pixels. A very limited but true direct color system, there are 3 bits for each of the R and G components, the normal human eye is less sensitive to the blue component than to the red or green, so it is assigned one bit less than the others. Used, amongst others, in the MSX2 system series of computers in the early to mid 1990s, do not confuse with an indexed color depth of 8bpp. High color supports 15/16-bit for three RGB colors, in 16-bit direct color, there can be 4 bits for each of the R, G, and B components, plus optionally 4 bits for alpha, enabling 4,096 different colors with 16 levels of transparency. Or in some systems there can be 5 bits per color component and 1 bit of alpha, or there can be 5 bits for red,6 bits for green and these color depths are sometimes used in small devices with a color display, such as mobile telephones. Variants with 5 or more bits per component are sometimes called high color. More expensive LCDs can display 24-bit or greater color depth, true color supports 24-bit for three RGB colors. Usually, true color is defined to mean 256 shades of red, green, the human eye can discriminate up to ten million colors. Color processing in the eye occurs through retinal cone cells which are of three types, although not corresponding to red, green and blue hues, true color can also refer to an RGB display-mode that does not need a color look-up table
4.
Binary image
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A binary image is a digital image that has only two possible values for each pixel. Typically, the two used for a binary image are black and white, though any two colors can be used. The color used for the object in the image is the foreground color while the rest of the image is the background color, in the document-scanning industry, this is often referred to as bi-tonal. Binary images are also called bi-level or two-level and this means that each pixel is stored as a single bit—i. e. The names black-and-white, B&W, monochrome or monochromatic are often used for this concept, in Photoshop parlance, a binary image is the same as an image in Bitmap mode. Binary images often arise in digital image processing as masks or as the result of operations such as segmentation, thresholding. Some input/output devices, such as printers, fax machines. A binary image can be stored in memory as a bitmap, a 640×480 image requires 37.5 KiB of storage. Because of the size of the image files, fax machine. Most binary images also compress well with simple run-length compression schemes, binary images can be interpreted as subsets of the two-dimensional integer lattice Z2, the field of morphological image processing was largely inspired by this view. An entire class of operations on binary images operates on a 3×3 window of the image and this contains nine pixels, so 512 possible values. Considering only the central pixel, it is possible to define whether it remains set or unset, examples of such operations are thinning, dilating, finding branch points and endpoints, removing isolated pixels, shifting the image a pixel in any direction, and breaking H-connections. Conways Game of Life is also an example of a 3×3 window operation, another class of operations is based on the notion of filtering with a structuring element. The structuring element is binary image, usually small, which is passed over the target image, since the pixels can only have two values, the morphological operations are erosion and dilation. Opening tends to enlarge small holes, remove objects. Closing retains small objects, removes holes, and joins objects, a very important characteristic of a binary image is the distance transform. This gives the distance of every set pixel from the nearest unset pixel, the distance transform can be efficiently calculated. It allows efficient computation of Voronoi diagrams, where each pixel in an image is assigned to the nearest of a set of points and it also allows skeletonization, which differs from thinning in that skeletons allow recovery of the original image
5.
8-bit color
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8-bit color graphics is a method of storing image information in a computers memory or in an image file, such that each pixel is represented by one 8-bit byte. The maximum number of colors that can be displayed at any one time is 256, there are two forms of 8-bit color graphics. The most common uses a palette of 256 colors, where each of the 256 entries in the palette map is given red, green. In most color maps, each color is chosen from a palette of 16,777,216 colors. But in the original VGA cards 320x200 mode,256 on-screen colors could be chosen from a palette of 262,144 colors, some older cards prior to the VGA can only choose the 256-color palette from 4,096 colors. The other form is where the 8 bits directly describe red, green and this second form is often called 8-bit truecolor, as it does not use a palette at all, and is thus more similar to the 15-bit, 16-bit, and 24-bit truecolor modes. Bit 76543210 Data R R R G G G B B Most 8-bit image formats store a local palette of 256 colors in addition to the raw image data. If such an image is to be displayed on 8-bit graphics hardware and this can result in other images on the screen having wildly distorted colors due to differences in their palettes. For this reason, on 8-bit graphics hardware, programs such as web browsers must address this issue when simultaneously displaying multiple images from different sources. Each image may have its own palette, but the colors in each image will be remapped to a single palette, currently, most graphics hardware runs in 24-bit truecolor or 32-bit truecolor, and this problem is largely a thing of the past. However, some remote desktop software can switch to 8-bit color to conserve bandwidth, planar Packed pixel 15/16-bit color 24-bit color Color depth List of palettes
6.
High color
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High color graphics is a method of storing image information in a computers memory such that each pixel is represented by two bytes. Usually the color is represented by all 16 bits, but some also support 15-bit high color. More recently, high color has been used by Microsoft to distinguish display systems that can make use of more than 8-bits per color channel from traditional 8-bit per color channel formats and this is a distinct usage from the 15-bit or 16-bit formats traditionally associated with the phrase high color. This allows 32,768 possible colors for each pixel, when all 16 bits are used, one of the components gets an extra bit, allowing 64 levels of intensity for that component, and a total of 65,536 available colors. This can lead to discrepancies in encoding, e. g. when one wishes to encode the 24-bit color RGB with 16 bits. The red and blue channels will take the five most significant bits, the green channel, with six bits of precision, will have a binary value of 001010, or 10 on a scale from 0 to 63. Because of this, the color RGB will have a purple tinge when displayed in 16 bits. Note that 40 on a scale from 0 to 255 is 15. 7%, green is usually chosen for the extra bit in 16 bits because the human eye has its highest sensitivity for green shades. For a demonstration, look closely at the picture where dark shades of red, green. Readers with normal vision should see the individual shades of green relatively easily, while the shades of red should be difficult to see, and the shades of blue are likely indistinguishable. More rarely, some systems support having the extra bit of depth on the red or blue channel. As a result, some image formats can save paletted 16-bit images with an embedded CLUT, 24-bit color 30/36/48-bit color Color depth Planar Packed pixel List of monochrome and RGB palettes — 15-bit RGB and 16-bit RGB sections
7.
Indexed color
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It is a form of vector quantization compression. When an image is encoded in this way, color information is not directly carried by the pixel data, but is stored in a separate piece of data called a palette. Every element in the array represents a color, indexed by its position within the array, the individual entries are sometimes known as color registers. The image pixels do not contain the full specification of its color and this technique is sometimes referred as pseudocolor or indirect color, as colors are addressed indirectly. Perhaps the first device that supported palette colors was a frame buffer, described in 1975 by Kajiya, Sutherland. This supported a palette of 256 36-bit RGB colors, the palette itself stores a limited number of distinct colors,4,16 or 256 are the most common cases. These limits are imposed by the target architectures display adapter hardware. While 256 values can be fit into a single 8-bit byte, sometimes, 1-bit values can be used, and then up to eight pixels can be packed into a single byte, such images are considered binary images and not an indexed color image. If simple video overlay is intended through a transparent color, one entry is specifically reserved for this purpose. Some machines, such as the MSX series, had the transparent color reserved by hardware, indexed color images with palette sizes beyond 256 entries are rare. The practical limit is around 12-bit per pixel,4,096 different indices, to use indexed 16 bpp or more does not provide the benefits of the indexed color images nature, due to the color palette size in bytes being greater than the raw image data itself. Also, useful direct RGB Highcolor modes can be used from 15 bpp, if an image has many subtle color shades, it is necessary to select a limited repertoire of colors to approximate the image using color quantization. Such a palette is frequently insufficient to represent the image accurately, many early personal and home computers had very limited hardware palettes that could produce a very small set of colors. In these cases, each pixels value mapped directly onto one of these colors, well-known examples include the Apple II, Commodore 64 and IBM PC CGA, all of which included hardware that could produce a fixed set of 16 colors. In these cases, an image can encode each pixel with 4-bits, in most cases, however, the display hardware supports additional modes where only a subset of those colors can be used in a single image, a useful technique to save memory. For instance, the CGAs 320×200 resolution mode could show only four of the 16 colors at one time, as the palettes were entirely proprietary, an image generated on one platform cannot be directly viewed properly on another. Other machines of this era had the ability to generate a set of colors. Examples include the 256-color palette on Atari 8-bit machines or the 4,096 colors of the VT241 terminal in ReGIS graphics mode
8.
Palette (computing)
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In computer graphics, a palette is a finite set of colors. Palettes can be optimized to improve accuracy in the presence of software or hardware constraints. Depending on the context, the palette and related terms such as Web palette. Selected colors or picked colors, In this case, the selection, generally from a wider explicitly available full palette, is always chosen by software. For example, the standard VGA display adapter is said to provide a palette of 256 simultaneous colors from a total of 262,144 different colors, default palette or system palette, The given selected colors have been officially standardized by some body or corporation. For example, the well known Web-safe colors for use with Internet browsers, on an individual image, color map or color table, The limited color selection is stored inside the given indexed color image file. For example, the registers of the Commodore Amiga are known both as their color palette and their CLUT, depending on sources. GUI palettes An arrangement of a set of user or system colors that can be chosen. In such cases, the color palette or user color palette are common equivalents. This usage resembles a true artists palette, a palette for choosing colors can be also a floating palette. An application can, in turn, show different image thumbnails in a mosaic on screen. It is obvious that the program cannot load all the adaptive palettes of every displayed image thumbnail at the time in the hardware color registers. A solution is to use a unique, common master palette or universal palette and this is done by selecting colors in such way that the master palette comprises a full RGB color space in miniature, limiting the possible levels that the red, green and blue components may have. This kind of arrangement is referred as a uniform palette. The normal human eye has sensibility to the three colors in different degrees, the more to the green, the less to the blue. So RGB arrangements can take advantage of this by assigning more levels for the green component and it is more general to use only 6R×6G×6B =216, 6R×8G×5B =240 or 6R×7G×6B =252, which leave room for some reserved colors. This way, and with further dithering, the color image can nearly match the original. But this creates a heavy dependence between the pixels and its adaptive palette
9.
RGB color model
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The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three primary colors, red, green and blue. Before the electronic age, the RGB color model already had a theory behind it. Thus an RGB value does not define the same color across devices without some kind of color management, typical RGB input devices are color TV and video cameras, image scanners, video games, and digital cameras. Typical RGB output devices are TV sets of technologies, computer and mobile phone displays, video projectors, multicolor LED displays. Color printers, on the hand are not RGB devices. This article discusses concepts common to all the different color spaces that use the RGB color model, to form a color with RGB, three light beams must be superimposed. Each of the three beams is called a component of color, and each of them can have an arbitrary intensity, from fully off to fully on. The RGB color model is additive in the sense that the three beams are added together, and their light spectra add, wavelength for wavelength. This is essentially opposite to the color model that applies to paints, inks, dyes. When the intensities for all the components are the same, the result is a shade of gray, darker or lighter depending on the intensity. When the intensities are different, the result is a colorized hue, a secondary color is formed by the sum of two primary colors of equal intensity, cyan is green+blue, magenta is red+blue, and yellow is red+green. The RGB color model itself does not define what is meant by red, green and blue colorimetrically, and so the results of mixing them are not specified as absolute, but relative to the primary colors. When the exact chromaticities of the red, green and blue primaries are defined, the normal three kinds of light-sensitive photoreceptor cells in the human eye respond most to yellow, green, and violet light. As an example, suppose that light in the range of wavelengths enters the eye. Light of these wavelengths would activate both the medium and long wavelength cones of the retina, but not equally—the long-wavelength cells will respond more, the difference in the response can be detected by the brain, and this difference is the basis of our perception of orange. Thus, the appearance of an object results from light from the object entering our eye and stimulating the different cones simultaneously. The first experiments with RGB in early color photography were made in 1861 by Maxwell himself, to reproduce the color photograph, three matching projections over a screen in a dark room were necessary
10.
Photography
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Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic sensor, this produces an electrical charge at each pixel. A negative image on film is used to photographically create a positive image on a paper base, known as a print. The word photography was created from the Greek roots φωτός, genitive of φῶς, light and γραφή representation by means of lines or drawing, several people may have coined the same new term from these roots independently. Johann von Maedler, a Berlin astronomer, is credited in a 1932 German history of photography as having used it in an article published on 25 February 1839 in the German newspaper Vossische Zeitung. Both of these claims are now widely reported but apparently neither has ever been confirmed as beyond reasonable doubt. Credit has traditionally given to Sir John Herschel both for coining the word and for introducing it to the public. Photography is the result of combining several technical discoveries, later Greek mathematicians Aristotle and Euclid also independently described a pinhole camera in the 5th and 4th centuries BCE. Daniele Barbaro described a diaphragm in 1566, wilhelm Homberg described how light darkened some chemicals in 1694. The fiction book Giphantie, published in 1760, by French author Tiphaigne de la Roche, the discovery of the camera obscura that provides an image of a scene dates back to ancient China. Leonardo da Vinci mentions natural camera obscura that are formed by dark caves on the edge of a sunlit valley, a hole in the cave wall will act as a pinhole camera and project a laterally reversed, upside down image on a piece of paper. So the birth of photography was primarily concerned with inventing means to capture, renaissance painters used the camera obscura which, in fact, gives the optical rendering in color that dominates Western Art. The camera obscura literally means dark chamber in Latin and it is a box with a hole in it which allows light to go through and create an image onto the piece of paper. Around the year 1800, British inventor Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance and he used paper or white leather treated with silver nitrate. The shadow images eventually darkened all over, the first permanent photoetching was an image produced in 1822 by the French inventor Nicéphore Niépce, but it was destroyed in a later attempt to make prints from it. Niépce was successful again in 1825, in 1826 or 1827, he made the View from the Window at Le Gras, the earliest surviving photograph from nature. Because Niépces camera photographs required a long exposure, he sought to greatly improve his bitumen process or replace it with one that was more practical. With an eye to eventual commercial exploitation, the partners opted for total secrecy, Daguerres efforts culminated in what would later be named the daguerreotype process
11.
Computing
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Computing is any goal-oriented activity requiring, benefiting from, or creating a mathematical sequence of steps known as an algorithm — e. g. through computers. The field of computing includes computer engineering, software engineering, computer science, information systems, the ACM Computing Curricula 2005 defined computing as follows, In a general way, we can define computing to mean any goal-oriented activity requiring, benefiting from, or creating computers. For example, an information systems specialist will view computing somewhat differently from a software engineer, regardless of the context, doing computing well can be complicated and difficult. Because society needs people to do computing well, we must think of computing not only as a profession, the fundamental question underlying all computing is What can be automated. The term computing is also synonymous with counting and calculating, in earlier times, it was used in reference to the action performed by mechanical computing machines, and before that, to human computers. Computing is intimately tied to the representation of numbers, but long before abstractions like the number arose, there were mathematical concepts to serve the purposes of civilization. These concepts include one-to-one correspondence, comparison to a standard, the earliest known tool for use in computation was the abacus, and it was thought to have been invented in Babylon circa 2400 BC. Its original style of usage was by lines drawn in sand with pebbles, abaci, of a more modern design, are still used as calculation tools today. This was the first known computer and most advanced system of calculation known to date - preceding Greek methods by 2,000 years. The first recorded idea of using electronics for computing was the 1931 paper The Use of Thyratrons for High Speed Automatic Counting of Physical Phenomena by C. E. Wynn-Williams. Claude Shannons 1938 paper A Symbolic Analysis of Relay and Switching Circuits then introduced the idea of using electronics for Boolean algebraic operations, a computer is a machine that manipulates data according to a set of instructions called a computer program. The program has a form that the computer can use directly to execute the instructions. The same program in its source code form, enables a programmer to study. Because the instructions can be carried out in different types of computers, the execution process carries out the instructions in a computer program. Instructions express the computations performed by the computer and they trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions, computer software or just software, is a collection of computer programs and related data that provides the instructions for telling a computer what to do and how to do it. Software refers to one or more programs and data held in the storage of the computer for some purposes. In other words, software is a set of programs, procedures, algorithms, program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software
12.
Colorimetry
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Colorimetry is the science and technology used to quantify and describe physically the human color perception. Colorimetric equipment is similar to that used in spectrophotometry, some related equipment is also mentioned for completeness. A tristimulus colorimeter measures the values of a color. A spectroradiometer measures the spectral radiance or irradiance of a light source. A spectrophotometer measures the reflectance, transmittance, or relative irradiance of a color sample. A spectrocolorimeter is a spectrophotometer that can calculate tristimulus values, a densitometer measures the degree of light passing through or reflected by a subject. A color temperature meter measures the temperature of an incident illuminant. In digital imaging, colorimeters are tristimulus devices used for color calibration, accurate color profiles ensure consistency throughout the imaging workflow, from acquisition to output. Reflected color can be measured using a spectrophotometer, which takes measurements in the region of a given color sample. If the custom of taking readings at 10 nanometer increments is followed and these readings are typically used to draw the samples spectral reflectance curve —the most accurate data that can be provided regarding its characteristics. The readings by themselves are not as useful as their tristimulus values. For this purpose, a spectrocolorimeter may be used, a spectrocolorimeter is simply a spectrophotometer that can estimate tristimulus values by numerical integration. On the other hand, tristimulus colorimeters are purpose-built, cheaper, the CIE recommends using measurement intervals under 5 nm, even for smooth spectra. Sparser measurements fail to accurately characterize spiky emission spectra, such as that of the red phosphor of a CRT display, photographers and cinematographers use information provided by these meters to decide what color balancing should be done to make different light sources appear to have the same color temperature. Internally the meter is typically a silicon photodiode tristimulus colorimeter, photometry Radiometry Schanda, János D. Colorimetry. Gardner, James L. Comparison of Calibration Methods for Tristimulus Colorimeters, journal of Research of the National Institute of Standards and Technology. Overview of the development and applications of colorimetry, optronik - Photometers An informative brochure with background information and specifications of their equipment. The section provides information on numerical scales and indices that are used throughout the world to remove subjective measurements, TS NIST Publications related to colorimetry
13.
Image
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Images may be two-dimensional, such as a photograph or screen display, or three-dimensional, such as a statue or hologram. They may be captured by optical devices – such as cameras, mirrors, lenses, telescopes, microscopes, etc. and natural objects and phenomena, such as the human eye or water. The word image is used in the broader sense of any two-dimensional figure such as a map, a graph. A volatile image is one that only for a short period of time. This may be a reflection of an object by a mirror, a fixed image, also called a hard copy, is one that has been recorded on a material object, such as paper or textile by photography or any other digital process. A mental image exists in a mind, as something one remembers or imagines. The subject of an image need not be real, it may be a concept, such as a graph, function. For example, Sigmund Freud claimed to have dreamed purely in aural-images of dialogs, a still image is a single static image, as distinguished from a kinetic image. This phrase is used in photography, visual media and the industry to emphasize that one is not talking about movies. A film still is a taken on the set of a movie or television program during production. In literature, imagery is a picture which appeals to the senses. It can both be figurative and literal, a moving image is typically a movie or video, including digital video. It could also be an animated display such as a zoetrope, library of Congress – Format Descriptions for Still Images Image Processing – Online Open Research Group Legal Issues Regarding Images Image Copyright Case
14.
Pixel
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The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a grid, and are often represented using dots or squares. Each pixel is a sample of an image, more samples typically provide more accurate representations of the original. The intensity of each pixel is variable, in color imaging systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black. The word pixel is based on a contraction of pix and el, the word pixel was first published in 1965 by Frederic C. Billingsley of JPL, to describe the elements of video images from space probes to the Moon. Billingsley had learned the word from Keith E. McFarland, at the Link Division of General Precision in Palo Alto, McFarland said simply it was in use at the time. The word is a combination of pix, for picture, the word pix appeared in Variety magazine headlines in 1932, as an abbreviation for the word pictures, in reference to movies. By 1938, pix was being used in reference to pictures by photojournalists. The concept of a picture element dates to the earliest days of television, some authors explain pixel as picture cell, as early as 1972. In graphics and in image and video processing, pel is often used instead of pixel, for example, IBM used it in their Technical Reference for the original PC. A pixel is generally thought of as the smallest single component of a digital image, however, the definition is highly context-sensitive. For example, there can be printed pixels in a page, or pixels carried by electronic signals, or represented by digital values, or pixels on a display device, or pixels in a digital camera. This list is not exhaustive and, depending on context, synonyms include pel, sample, byte, bit, dot, Pixels can be used as a unit of measure such as,2400 pixels per inch,640 pixels per line, or spaced 10 pixels apart. For example, a high-quality photographic image may be printed with 600 ppi on a 1200 dpi inkjet printer, even higher dpi numbers, such as the 4800 dpi quoted by printer manufacturers since 2002, do not mean much in terms of achievable resolution. The more pixels used to represent an image, the closer the result can resemble the original, the number of pixels in an image is sometimes called the resolution, though resolution has a more specific definition.3 megapixels. The pixels, or color samples, that form an image may or may not be in one-to-one correspondence with screen pixels. In computing, a composed of pixels is known as a bitmapped image or a raster image
15.
Sampling (signal processing)
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In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a wave to a sequence of samples. A sample is a value or set of values at a point in time and/or space, a sampler is a subsystem or operation that extracts samples from a continuous signal. A theoretical ideal sampler produces samples equivalent to the value of the continuous signal at the desired points. Sampling can be done for functions varying in space, time, or any other dimension, then the sampled function is given by the sequence, s, for integer values of n. The sampling frequency or sampling rate, fs, is the number of samples obtained in one second. Reconstructing a continuous function from samples is done by interpolation algorithms, the Whittaker–Shannon interpolation formula is mathematically equivalent to an ideal lowpass filter whose input is a sequence of Dirac delta functions that are modulated by the sample values. When the time interval between adjacent samples is a constant, the sequence of functions is called a Dirac comb. Mathematically, the modulated Dirac comb is equivalent to the product of the function with s. That purely mathematical abstraction is sometimes referred to as impulse sampling, most sampled signals are not simply stored and reconstructed. But the fidelity of a reconstruction is a customary measure of the effectiveness of sampling. That fidelity is reduced when s contains frequency components whose periodicity is smaller than 2 samples, the quantity ½ cycles/sample × fs samples/sec = fs/2 cycles/sec is known as the Nyquist frequency of the sampler. Therefore, s is usually the output of a lowpass filter, without an anti-aliasing filter, frequencies higher than the Nyquist frequency will influence the samples in a way that is misinterpreted by the interpolation process. In practice, the signal is sampled using an analog-to-digital converter. This results in deviations from the theoretically perfect reconstruction, collectively referred to as distortion, various types of distortion can occur, including, Aliasing. Some amount of aliasing is inevitable because only theoretical, infinitely long, Aliasing can be made arbitrarily small by using a sufficiently large order of the anti-aliasing filter. Aperture error results from the fact that the sample is obtained as a time average within a sampling region, in a capacitor-based sample and hold circuit, aperture error is introduced because the capacitor cannot instantly change voltage thus requiring the sample to have non-zero width. Jitter or deviation from the precise sample timing intervals, noise, including thermal sensor noise, analog circuit noise, etc
16.
Luminous intensity
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The SI unit of luminous intensity is the candela, an SI base unit. Photometry deals with the measurement of light as perceived by human eyes. The human eye can see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions, the eye is most sensitive to light at 555 nm. Light with the radiant intensity at other wavelengths has a lower luminous intensity. The curve which measures the response of the eye to light is a defined standard. This curve, denoted V or y ¯, is based on an average of widely differing experimental data from scientists using different measurement techniques, for instance, the measured responses of the eye to violet light varied by a factor of ten. Luminous intensity should not be confused with another unit, luminous flux. Luminous intensity is the power per unit solid angle. If a lamp has a 1 lumen bulb and the optics of the lamp are set up to focus the light evenly into a 1 steradian beam, if the optics were changed to concentrate the beam into 1/2 steradian then the source would have a luminous intensity of 2 candela. The resulting beam is narrower and brighter, though its luminous flux remains unchanged, luminous intensity is also not the same as the radiant intensity, the corresponding objective physical quantity used in the measurement science of radiometry. Like other SI base units, the candela has an operational definition—it is defined by the description of a process that will produce one candela of luminous intensity. The frequency of light used in the definition corresponds to a wavelength of 555 nm, if the source emitted uniformly in all directions, the total radiant flux would be about 18.40 mW, since there are 4π steradians in a sphere. A typical candle produces very roughly one candela of luminous intensity, prior to the definition of the candela, a variety of units for luminous intensity were used in various countries. These were typically based on the brightness of the flame from a candle of defined composition. One of the best-known of these standards was the English standard, one candlepower was the light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour. Germany, Austria, and Scandinavia used the Hefnerkerze, a based on the output of a Hefner lamp. In 1881, Jules Violle proposed the Violle as a unit of luminous intensity, all of these units were superseded by the definition of the candela
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Black and white
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Black and white, often abbreviated B/W or B&W, and hyphenated black-and-white when used as an adjective, is any of several monochrome forms in visual arts. Black-and-white images are not usually starkly contrasted black and white and they combine black and white in a continuum producing a range of shades of gray. Even when most studios had the capability to make color films they were not heavily utilized as using the Technicolor process was expensive, for the years 1940–1966, a separate Academy Award for Best Art Direction was given for black-and-white movies along with one for color. Television, Television program was first transmitted in black-and-white, scottish inventor John Logie Baird demonstrated the worlds first color television transmission on July 3,1928 using a mechanical process. Some color broadcasts in the US began in the 1950s, with color becoming common in industrialized nations during the late 1960s. In the United States, the Federal Communications Commission settled on a color NTSC standard in 1953, color television became more widespread in the U. S. between 1963 and 1967, when the CBS and ABC networks joined NBC in broadcasting full color schedules. Canada began airing color television in 1966 while the United Kingdom began to use a different color system from July 1967 known as PAL. The Republic Of Ireland followed in 1970, in China, black and white television sets were the norm until as late as the 1990s, color TVs not outselling them until about 1989. While seldom used now, many consumer camcorders have the ability to record in black-and-white. Photography, Photographs were either black-and-white or shades of sepia, color photography was originally rare and expensive and again often containing inaccurate hues. Color photography became more common from the mid-20th century, Today, black-and-white is a niche market for photographers who use the medium for artistic purposes. This can take the form of film or digital conversion to grayscale. For amateur use certain companies such as Kodak manufactured black-and-white disposable cameras until 2009, also, certain films are produced today which give black-and-white images using the ubiquitous C41 color process. Printing press, Most American newspapers were black-and-white until the early 1980s, The New York Times, some claim that USA Today was the major impetus for the change to color. In the UK, color was only introduced from the mid-1980s. Even today, many newspapers restrict color photographs to the front, similarly, daily comic strips in newspapers were traditionally black-and-white with color reserved for Sunday strips. Sometimes color is reserved for the cover, magazines such as Jet magazine were either all or mostly black-and-white until the end of the 2000s when it became all-color. Manga are typically published in black-and-white although now it is part of its image, many school yearbooks are still entirely or mostly in black-and-white
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Grey
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Grey or gray is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is a color without color and this means that there are equal components of red, green, and blue. The variations in intensity of these colors uniformly produce different shades of grey and it is the color of a cloud-covered sky, of ash and of lead. The first recorded use of grey as a name in the English language was in AD700. Grey is the dominant spelling in European and Commonwealth English, although remained in common usage in the UK until the second half of the 20th century. Gray has been the preferred American spelling since approximately 1825, although grey is an accepted variant, in Europe and the United States, surveys show that grey is the color most commonly associated with neutrality, conformity, boredom, uncertainty, old age, indifference, and modesty. Only one percent of respondents chose it as their favorite color, Grey comes from the Middle English grai or grei, from the Anglo-Saxon graeg, and is related to the Dutch grauw and grijs and German grau. The first recorded use of grey as a name in the English language was in AD700. In antiquity and the Middle Ages, grey was the color of undyed wool, and thus was the color most commonly worn by peasants and the poor. It was also the color worn by monks of the Franciscan order, Cistercian Order, Franciscan monks in England and Scotland were commonly known as the Grey friars, and that name is now attached to many places in Great Britain. During the Renaissance and the Baroque, grey began to play an important role in fashion, Black became the most popular color of the nobility, particularly in Italy, France, and Spain, and grey and white were harmonious with it. Grey was also used for the drawing of oil paintings. The painting would first be composed in grey and white, and then the colors, made with thin transparent glazes, the grisaille beneath would provide the shading, visible through the layers of color. Sometimes the grisaille was simply left uncovered, giving the appearance of carved stone, Grey was a particularly good background color for gold and for skin tones. It became the most common background for the portraits of Rembrandt Van Rijn and for many of the paintings of El Greco, the palette of Rembrandt was composed almost entirely of somber colors. Over this he put a layer of glaze made of mixture of blue smalt, red ochre. Using these ingredients and many others, he made greys which had, according to art historian Philip Ball, the warm, dark and rich greys and browns served to emphasize the golden light on the faces in the paintings. Grey became a fashionable color in the 18th century, both for womens dresses and for mens waistcoats and coats
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Color
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Color or colour is the characteristic of human visual perception described through color categories, with names such as red, yellow, purple, or blue. This perception of color derives from the stimulation of cells in the human eye by electromagnetic radiation in the spectrum of light. Color categories and physical specifications of color are associated with objects through the wavelength of the light that is reflected from them and this reflection is governed by the objects physical properties such as light absorption, emission spectra, etc. By defining a color space, colors can be identified numerically by coordinates, there may also be more than three color dimensions in other color spaces, such as in the CMYK color model, wherein one of the dimensions relates to a colours colorfulness). The photo-receptivity of the eyes of species also varies considerably from our own. Honeybees and bumblebees for instance have trichromatic color vision sensitive to ultraviolet but is insensitive to red, papilio butterflies possess six types of photoreceptors and may have pentachromatic vision. The most complex color vision system in the kingdom has been found in stomatopods with up to 12 spectral receptor types thought to work as multiple dichromatic units. The science of color is sometimes called chromatics, colorimetry, or simply color science and it includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range. Electromagnetic radiation is characterized by its wavelength and its intensity, when the wavelength is within the visible spectrum, it is known as visible light. Most light sources emit light at different wavelengths, a sources spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, in each such class the members are called metamers of the color in question. The table at right shows approximate frequencies and wavelengths for various pure spectral colors, the wavelengths listed are as measured in air or vacuum. A common list identifies six main bands, red, orange, yellow, green, blue, Newtons conception included a seventh color, indigo, between blue and violet. It is possible that what Newton referred to as blue is nearer to what today is known as cyan, the color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain. Some objects not only light, but also transmit light or emit light themselves. This effect is known as color constancy, opaque objects that do not reflect specularly have their color determined by which wavelengths of light they scatter strongly. If objects scatter all wavelengths with roughly equal strength, they appear white, if they absorb all wavelengths, they appear black. Opaque objects that reflect light of different wavelengths with different efficiencies look like mirrors tinted with colors determined by those differences
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Black
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Black is the darkest color resulting from the absence or complete absorption of light. Like white and grey, it is a color, literally a color without hue. It is one of the four colors in the CMYK color model, along with cyan, yellow. Black is often used to represent darkness, it is the symbolic opposite of white, Black was one of the first colors used by artists in neolithic cave paintings. In the 14th century, it began to be worn by royalty and it became the color worn by English romantic poets, businessmen and statesmen in the 19th century, and a high fashion color in the 20th century. In the Roman Empire, it became the color of mourning, according to surveys in Europe and North America, it is the color most commonly associated with mourning, the end, secrets, magic, force, violence, evil, and elegance. More distant cognates include Latin flagrare, and Ancient Greek phlegein, the Ancient Greeks sometimes used the same word to name different colors, if they had the same intensity. Kuanos could mean both dark blue and black, the Ancient Romans had two words for black, ater was a flat, dull black, while niger was a brilliant, saturated black. Ater has vanished from the vocabulary, but niger was the source of the country name Nigeria the English word Negro, old High German also had two words for black, swartz for dull black and blach for a luminous black. These are parallelled in Middle English by the terms swart for dull black, swart still survives as the word swarthy, while blaek became the modern English black. In heraldry, the used for the black color is sable, named for the black fur of the sable. Black was one of the first colors used in art, the Lascaux Cave in France contains drawings of bulls and other animals drawn by paleolithic artists between 18,000 and 17,000 years ago. They began by using charcoal, and then made more vivid black pigments by burning bones or grinding a powder of manganese oxide, for the ancient Egyptians, black had positive associations, being the color of fertility and the rich black soil flooded by the Nile. It was the color of Anubis, the god of the underworld, who took the form of a black jackal, and offered protection against evil to the dead. For the ancient Greeks, black was also the color of the underworld, separated from the world of the living by the river Acheron and those who had committed the worst sins were sent to Tartarus, the deepest and darkest level. In the center was the palace of Hades, the king of the underworld, Black was one of the most important colors used by ancient Greek artists. In the 6th century BC, they began making pottery and later red figure pottery. In black-figure pottery, the artist would paint figures with a clay slip on a red clay pot
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White
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White is an achromatic color, a color without hue. An incoming light to the eye that stimulates all its three types of color sensitive cone cells in nearly equal amounts results in white. White is one of the most common colors in nature, the color of sunlight, snow, milk, chalk, limestone, in many cultures white represents or signifies purity, innocence, and light, and is the symbolic opposite of black, or darkness. According to surveys in Europe and the United States, white is the color most often associated with perfection, the good, honesty, cleanliness, the beginning, the new, neutrality, and exactitude. In ancient Egypt and ancient Rome, priestesses wore white as a symbol of purity, in the Middle Ages and Renaissance a white unicorn symbolized chastity, and a white lamb sacrifice and purity, the widows of kings dressed in white rather than black as the color of mourning. It was also used in 20th century modern architecture as a symbol of modernity, simplicity. White is an important color for almost all world religions, the Pope, the head of the Roman Catholic Church, has worn white since 1566, as a symbol of purity and sacrifice. In Islam, and in the Shinto religion of Japan, it is worn by pilgrims, in Western cultures and in Japan, white is the most common color for wedding dresses, symbolizing purity and virginity. In many Asian cultures, white is also the color of mourning, the white color on television screens and computer monitors is created with the RGB color model by mixing red, green and blue light at equal intensities. The word white continues Old English hwīt, ultimately from a Common Germanic *χwītaz also reflected in OHG wîz, ON hvítr, the root is ultimately from Proto-Indo-European language *kwid-, surviving also in Sanskrit śveta to be white or bright and Slavonic světŭ light. The Icelandic word for white, hvítur, is derived from the Old Norse form of the word hvítr. Common Germanic also had the word *blankaz, borrowed into Late Latin as *blancus, the antonym of white is black. Some non-European languages have a variety of terms for white. The Inuit language has seven different words for seven different nuances of white, Japanese has six different words, depending upon brilliance or dullness, or if the color is inert or dynamic. White was one of the first colors used in art, the Lascaux Cave in France contains drawings of bulls and other animals drawn by paleolithic artists between 18,000 and 17,000 years ago. Paleolithic artists used calcite or chalk, they sometimes as a background, sometimes as a highlight, along with charcoal and red, in ancient Egypt, white was connected with the goddess Isis. The priests and priestesses of Isis dressed only in white linen, in Greece and other ancient civilizations, white was often associated with mothers milk. In Greek mythology, the chief god Zeus was nourished at the breast of the nymph Amalthea, in the Talmud, milk was one of four sacred substances, along with wine, honey, and the rose
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Spectral color
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A spectral color is a color that is evoked by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths, also known as monochromatic light. Every wavelength of light is perceived as a spectral color, in a continuous spectrum. The spectrum is divided into named colors, though any division is somewhat arbitrary. Traditional colors include, red, orange, yellow, green, blue, and violet. The division used by Isaac Newton, in his wheel, was, red, orange, yellow, green, blue, indigo and violet. In modern divisions of the spectrum, indigo is often omitted, if luminance is counted, then spectral colors form a surface, otherwise their locus is a curve in a two-dimensional chromaticity space. Theoretically, only RGB-implemented colors which might be really spectral are its primaries, red, green, some samples in the table below provide only rough approximations of spectral and near-spectral colors. Ranges of wavelengths and frequencies are only approximate, among some of the colors that are not spectral colors are, Grayscale colors, such as white, gray, and black. Any color obtained by mixing a gray-scale color and another color, violet-red colors, which in color theory include line of purples colors, and other variations of purple and red. Impossible colors, which can not be seen under normal viewing of light, such as over-saturated colors or colors that are seemingly brighter than white
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Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
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Electromagnetic spectrum
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The electromagnetic spectrum is the collective term for all known frequencies and their linked wavelengths of the known photons. The electromagnetic spectrum of an object has a different meaning, and is instead the characteristic distribution of radiation emitted or absorbed by that particular object. Visible light lies toward the end, with wavelengths from 400 to 700 nanometres. The limit for long wavelengths is the size of the universe itself, until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous. Nearly all types of radiation can be used for spectroscopy, to study. Other technological uses are described under electromagnetic radiation, for most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, the study of light continued, and during the 16th and 17th centuries conflicting theories regarded light as either a wave or a particle. The first discovery of electromagnetic radiation other than visible light came in 1800 and he was studying the temperature of different colors by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red and he theorized that this temperature change was due to calorific rays that were a type of light ray that could not be seen. The next year, Johann Ritter, working at the end of the spectrum. These behaved similarly to visible light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation, during the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and behavior of, analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light. This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave, maxwells equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light. This was the first indication of the existence of the electromagnetic spectrum. Maxwells predicted waves included waves at very low compared to infrared. Hertz found the waves and was able to infer that they traveled at the speed of light, Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin, in a later experiment, Hertz similarly produced and measured the properties of microwaves
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Infrared
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It extends from the nominal red edge of the visible spectrum at 700 nanometers, to 1000000 nm. Most of the radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon, slightly more than half of the total energy from the Sun was eventually found to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an effect on Earths climate. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements and it excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range, Infrared radiation is used in industrial, scientific, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected, Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatuses. Thermal-infrared imaging is used extensively for military and civilian purposes, military applications include target acquisition, surveillance, night vision, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm, Infrared radiation extends from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm. This range of wavelengths corresponds to a range of approximately 430 THz down to 300 GHz. Below infrared is the portion of the electromagnetic spectrum. Sunlight, at a temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level, of this energy,527 watts is infrared radiation,445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight. Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wiens displacement law. Therefore, the band is often subdivided into smaller sections. Due to the nature of the blackbody radiation curves, typical hot objects, such as exhaust pipes, the three regions are used for observation of different temperature ranges, and hence different environments in space
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Visible spectrum
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The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm, in terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not, however, contain all the colors that the human eyes, unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths. Colors containing only one wavelength are called pure colors or spectral colors. Visible wavelengths pass through the window, the region of the electromagnetic spectrum that allows wavelengths to pass largely unattenuated through the Earths atmosphere. An example of this phenomenon is that clean air scatters blue light more than red wavelengths, the optical window is also referred to as the visible window because it overlaps the human visible response spectrum. The near infrared window lies just out of the vision, as well as the Medium Wavelength IR window. In the 13th century, Roger Bacon theorized that rainbows were produced by a process to the passage of light through glass or crystal. In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light and he was the first to use the word spectrum in this sense in print in 1671 in describing his experiments in optics. The result is red light is bent less sharply than violet as it passes through the prism. Newton divided the spectrum into seven named colors, red, orange, yellow, green, blue, indigo, the human eye is relatively insensitive to indigos frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right. However, the evidence indicates that what Newton meant by indigo, comparing Newtons observation of prismatic colors to a color image of the visible light spectrum shows that indigo corresponds to what is today called blue, whereas blue corresponds to cyan. In the 18th century, Goethe wrote about optical spectra in his Theory of Colours, Goethe used the word spectrum to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors. Goethe argued that the spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow, the spectrum appears only when these edges are close enough to overlap. Young was the first to measure the wavelengths of different colors of light, the connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century
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Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
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Photometry (optics)
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Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power, in modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. The human eye is not equally sensitive to all wavelengths of visible light, photometry attempts to account for this by weighing the measured power at each wavelength with a factor that represents how sensitive the eye is at that wavelength. The standardized model of the response to light as a function of wavelength is given by the luminosity function. The eye has different responses as a function of wavelength when it is adapted to light conditions, photopic vision is characteristic of the eyes response at luminance levels over three candela per square metre. Scotopic vision occurs below 2 × 10−5 cd/m2, mesopic vision occurs between these limits and is not well characterised for spectral response. Measurement of the effects of electromagnetic radiation became a field of study as early as the end of 18th century, measurement techniques varied depending on the effects under study and gave rise to different nomenclature. The total heating effect of infrared radiation as measured by thermometers led to development of radiometric units in terms of total energy, use of the human eye as a detector led to photometric units, weighted by the eyes response characteristic. Study of the effects of ultraviolet radiation led to characterization by the total dose or actinometric units expressed in photons per second. Many different units of measure are used for photometric measurements, people sometimes ask why there need to be so many different units, or ask for conversions between units that cant be converted. We are familiar with the idea that the adjective heavy can refer to weight or density, for example, offices are typically brightly illuminated by an array of many recessed fluorescent lights for a combined high luminous flux. A laser pointer has very low luminous flux but is bright in one direction. There are two systems of quantities known as photometric and radiometric quantities. Every quantity in one system has a quantity in the other system. For example, the eye responds much more strongly to light than to red. Watts are units of radiant flux while lumens are units of luminous flux, a comparison of the watt and the lumen illustrates the distinction between radiometric and photometric units. The watt is a unit of power and we are accustomed to thinking of light bulbs in terms of power in watts
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Color space
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A color space is a specific organization of colors. In combination with physical device profiling, it allows for reproducible representations of color, for example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB color model. When defining a color space, the reference standard is the CIELAB or CIEXYZ color spaces. For example, although several specific color spaces are based on the RGB color model, colors can be created in printing with color spaces based on the CMYK color model, using the subtractive primary colors of pigment. The resulting 3-D space provides a position for every possible color that can be created by combining those three pigments. Colors can be created on computer monitors with color spaces based on the RGB color model, a three-dimensional representation would assign each of the three colors to the X, Y, and Z axes. Note that colors generated on given monitor will be limited by the medium, such as the phosphor or filters. Another way of creating colors on a monitor is with an HSL or HSV color space, based on hue, saturation, with such a space, the variables are assigned to cylindrical coordinates. Many color spaces can be represented as three-dimensional values in this manner, but some have more, or fewer dimensions, Color space conversion is the translation of the representation of a color from one basis to another. The RGB color model is implemented in different ways, depending on the capabilities of the system used, by far the most common general-used incarnation as of 2006 is the 24-bit implementation, with 8 bits, or 256 discrete levels of color per channel. Any color space based on such a 24-bit RGB model is limited to a range of 256×256×256 ≈16.7 million colors. Some implementations use 16 bits per component for 48 bits total and this is especially important when working with wide-gamut color spaces, or when a large number of digital filtering algorithms are used consecutively. The same principle applies for any color space based on the color model. CIE1931 XYZ color space was one of the first attempts to produce a space based on measurements of human color perception. The CIERGB color space is a companion of CIE XYZ. Additional derivatives of CIE XYZ include the CIELUV, CIEUVW, RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color. RGB stores individual values for red, green and blue, RGBA is RGB with an additional channel, alpha, to indicate transparency. Common color spaces based on the RGB model include sRGB, Adobe RGB, ProPhoto RGB, scRGB, one starts with a white substrate, and uses ink to subtract color from white to create an image
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Printing
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Printing is a process for reproducing text and images using a master form or template. The earliest examples include Cylinder seals and other such as the Cyrus Cylinder. The earliest known form of printing came from China dating to before 220 A. D. Later developments in printing include the type, first developed by Bi Sheng in China around 1040 AD. Johannes Gutenberg introduced mechanical movable type printing to Europe in the 15th century, modern large-scale printing is typically done using a printing press, while small-scale printing is done free-form with a digital printer. Though paper is the most common material, it is frequently done on metals, plastics, cloth. On paper it is carried out as a large-scale industrial process and is an essential part of publishing. Woodblock printing is a technique for printing text, images or patterns that was used widely throughout East Asia and it originated in China in antiquity as a method of printing on textiles and later on paper. As a method of printing on cloth, the earliest surviving examples from China date to before 220 A. D, the earliest surviving woodblock printed fragments are from China. They are of silk printed with flowers in three colours from the Han Dynasty and they are the earliest example of woodblock printing on paper appeared in the mid-seventh century in China. By the ninth century, printing on paper had taken off, by the tenth century,400,000 copies of some sutras and pictures were printed, and the Confucian classics were in print. A skilled printer could print up to 2,000 double-page sheets per day, Printing spread early to Korea and Japan, which also used Chinese logograms, but the technique was also used in Turpan and Vietnam using a number of other scripts. This technique then spread to Persia and Russia and this technique was transmitted to Europe via the Islamic world, and by around 1400 was being used on paper for old master prints and playing cards. However, Arabs never used this to print the Quran because of the limits imposed by Islamic doctrine, block printing, called tarsh in Arabic developed in Arabic Egypt during the ninth-tenth centuries, mostly for prayers and amulets. There is some evidence to suggest that these print blocks made from non-wood materials, possibly tin, lead, the techniques employed are uncertain, however, and they appear to have had very little influence outside of the Muslim world. Though Europe adopted woodblock printing from the Muslim world, initially for fabric, block printing later went out of use in Islamic Central Asia after movable type printing was introduced from China. Block printing first came to Europe as a method for printing on cloth, images printed on cloth for religious purposes could be quite large and elaborate. When paper became relatively easily available, around 1400, the medium transferred very quickly to small religious images
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Halftone
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Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient-like effect. Halftone can also be used to specifically to the image that is produced by this process. This reproduction relies on an optical illusion, the tiny halftone dots are blended into smooth tones by the human eye. At a microscopic level, developed black-and-white photographic film also consists of two colors, and not an infinite range of continuous tones. The semi-opaque property of ink allows halftone dots of different colors to create another optical effect—full-color imagery, william Fox Talbot is credited with the idea of halftone printing. In a 1852 patent he suggested using photographic screens or veils in connection with an intaglio process. Several different kinds of screens were proposed during the following decades, one of the well known attempts was by Stephen H. Horgan while working for the New York Daily Graphic. The first printed photograph was an image of Steinway Hall in Manhattan published on December 2,1873, the Graphic then published the first reproduction of a photograph with a full tonal range in a newspaper on March 4,1880 with a crude halftone screen. The first truly successful commercial method was patented by Frederic Ives of Philadelphia in 1881, although he found a way of breaking up the image into dots of varying sizes, he did not make use of a screen. In 1882, the German Georg Meisenbach patented a process in England. His invention was based on the ideas of Berchtold and Swan. He used single lined screens which were turned during exposure to produce cross-lined effects and he was the first to achieve any commercial success with relief halftones. Shortly afterwards, Ives, this time in collaboration with Louis and Max Levy, improved the process further with the invention, the relief halftone process proved almost immediately to be a success. The use of blocks in popular journals became regular during the early 1890s. The development of printing methods for lithography appears to have followed a largely independent path. In the 1860s, A. Hoen & Co. focused on methods allowing artists to manipulate the tones of hand-worked printing stones, by the 1880s, Hoen was working on halftone methods that could be used in conjunction with either hand-worked or photolithographic stones. The most common method of creating screens—amplitude modulation—produces a regular grid of dots that vary in size, the other method of creating screens—frequency modulation—is used in a process also known as stochastic screening. Both modulation methods are named by analogy with the use of the terms in telecommunications, the resolution of a halftone screen is measured in lines per inch
32.
Rational number
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In mathematics, a rational number is any number that can be expressed as the quotient or fraction p/q of two integers, a numerator p and a non-zero denominator q. Since q may be equal to 1, every integer is a rational number, the decimal expansion of a rational number always either terminates after a finite number of digits or begins to repeat the same finite sequence of digits over and over. Moreover, any repeating or terminating decimal represents a rational number and these statements hold true not just for base 10, but also for any other integer base. A real number that is not rational is called irrational, irrational numbers include √2, π, e, and φ. The decimal expansion of an irrational number continues without repeating, since the set of rational numbers is countable, and the set of real numbers is uncountable, almost all real numbers are irrational. Rational numbers can be defined as equivalence classes of pairs of integers such that q ≠0, for the equivalence relation defined by ~ if. The rational numbers together with addition and multiplication form field which contains the integers and is contained in any field containing the integers, finite extensions of Q are called algebraic number fields, and the algebraic closure of Q is the field of algebraic numbers. In mathematical analysis, the numbers form a dense subset of the real numbers. The real numbers can be constructed from the numbers by completion, using Cauchy sequences, Dedekind cuts. The term rational in reference to the set Q refers to the fact that a number represents a ratio of two integers. In mathematics, rational is often used as a noun abbreviating rational number, the adjective rational sometimes means that the coefficients are rational numbers. However, a curve is not a curve defined over the rationals. Any integer n can be expressed as the rational number n/1, a b = c d if and only if a d = b c. Where both denominators are positive, a b < c d if and only if a d < b c. If either denominator is negative, the fractions must first be converted into equivalent forms with positive denominators, through the equations, − a − b = a b, two fractions are added as follows, a b + c d = a d + b c b d. A b − c d = a d − b c b d, the rule for multiplication is, a b ⋅ c d = a c b d. Where c ≠0, a b ÷ c d = a d b c, note that division is equivalent to multiplying by the reciprocal of the divisor fraction, a d b c = a b × d c. Additive and multiplicative inverses exist in the numbers, − = − a b = a − b and −1 = b a if a ≠0
33.
Quantization (signal processing)
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Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set. Rounding and truncation are typical examples of quantization processes, quantization is involved to some degree in nearly all digital signal processing, as the process of representing a signal in digital form ordinarily involves rounding. Quantization also forms the core of essentially all lossy compression algorithms, the difference between an input value and its quantized value is referred to as quantization error. A device or algorithmic function that performs quantization is called a quantizer, an analog-to-digital converter is an example of a quantizer. Because quantization is a mapping, it is an inherently non-linear. The set of input values may be infinitely large, and may possibly be continuous. The set of output values may be finite or countably infinite. The input and output involved in quantization can be defined in a rather general way. For example, vector quantization is the application of quantization to multi-dimensional input data, outside the realm of signal processing, this category may simply be called rounding or scalar quantization. An ADC can be modeled as two processes, sampling and quantization, sampling converts a voltage signal into a discrete-time signal. Quantization replaces each real number with an approximation from a set of discrete values. Most commonly, these values are represented as fixed-point words or floating-point words. Common word-lengths are 8-bit, 16-bit, 32-bit, and so on, quantizing a sequence of numbers produces a sequence of quantization errors which is sometimes modeled as an additive random signal called quantization noise because of its stochastic behavior. The more levels a quantizer uses, the lower is its noise power. In general, both ADC processes lose some information, so discrete-valued signals are only an approximation of the continuous-valued discrete-time signal, which is itself only an approximation of the original continuous-valued continuous-time signal. But both types of errors can, in theory, be made arbitrarily small by good design. In this second setting, the amount of introduced distortion may be managed carefully by sophisticated techniques, a quantizer designed for this purpose may be quite different and more elaborate in design than an ordinary rounding operation. It is in this domain that substantial rate–distortion theory analysis is likely to be applied, however, the same concepts actually apply in both use cases
34.
Binary code
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A binary code represents text, computer processor instructions, or other data using any two-symbol system, but often the binary number systems 0 and 1. The binary code assigns a pattern of digits to each character, instruction. For example, a string of eight bits can represent any of 256 possible values. In computing and telecommunications, binary codes are used for methods of encoding data, such as character strings. Those methods may use fixed-width or variable-width strings, there are many character sets and many character encodings for them. A bit string, interpreted as a number, can be translated into a decimal number. For example, the case a, if represented by the bit string 01100001. The modern binary system, the basis for binary code, was invented by Gottfried Leibniz in 1679. Leibnizs system uses 0 and 1, like the modern binary numeral system, Leibniz saw the hexagrams as an affirmation of the universality of his own religious beliefs. Binary numerals were central to Leibnizs theology and he believed that binary numbers were symbolic of the Christian idea of creatio ex nihilo or creation out of nothing. Leibniz was trying to find a system that converts logic’s verbal statements into a mathematical one. After his ideas were ignored, he came across a classic Chinese text called I Ching or ‘Book of Changes’, the book had confirmed his theory that life could be simplified or reduced down to a series of straightforward propositions. He created a system consisting of rows of zeros and ones, during this time period, Leibniz had not yet found a use for this system. Binary systems predating Leibniz also existed in the ancient world, the aforementioned I Ching that Leibniz encountered dates from the 9th century BC in China. The binary system of the I Ching, a text for divination, is based on the duality of yin, slit drums with binary tones are used to encode messages across Africa and Asia. The Indian scholar Pingala developed a system for describing prosody in his Chandashutram. The residents of the island of Mangareva in French Polynesia were using a hybrid binary-decimal system before 1450, the ordering is also the lexicographical order on sextuples of elements chosen from a two-element set. Boole’s system was based on binary, a yes-no, on-off approach that consisted of the three most basic operations, AND, OR, and NOT. Shannon wrote his thesis in 1937, which implemented his findings
35.
Byte
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The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of used to encode a single character of text in a computer. The size of the byte has historically been hardware dependent and no standards existed that mandated the size. The de-facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte, the international standard IEC 80000-13 codified this common meaning. Many types of applications use information representable in eight or fewer bits, the popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the 8-bit size. The unit symbol for the byte was designated as the upper-case letter B by the IEC and IEEE in contrast to the bit, internationally, the unit octet, symbol o, explicitly denotes a sequence of eight bits, eliminating the ambiguity of the byte. It is a respelling of bite to avoid accidental mutation to bit. Early computers used a variety of four-bit binary coded decimal representations and these representations included alphanumeric characters and special graphical symbols. S. Government and universities during the 1960s, the prominence of the System/360 led to the ubiquitous adoption of the eight-bit storage size, while in detail the EBCDIC and ASCII encoding schemes are different. In the early 1960s, AT&T introduced digital telephony first on long-distance trunk lines and these used the eight-bit µ-law encoding. This large investment promised to reduce costs for eight-bit data. The development of microprocessors in the 1970s popularized this storage size. A four-bit quantity is called a nibble, also nybble. The term octet is used to specify a size of eight bits. It is used extensively in protocol definitions, historically, the term octad or octade was used to denote eight bits as well at least in Western Europe, however, this usage is no longer common. The exact origin of the term is unclear, but it can be found in British, Dutch, and German sources of the 1960s and 1970s, and throughout the documentation of Philips mainframe computers. The unit symbol for the byte is specified in IEC 80000-13, IEEE1541, in the International System of Quantities, B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell, creating a conflict with the IEC specification. However, little danger of confusion exists, because the bel is a used unit
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Compression artifact
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A compression artifact is a noticeable distortion of media caused by the application of lossy compression. Lossy data compression involves discarding some of the data so that it becomes simplified enough to be stored within the desired disk space or be transmitted within the bandwidth limitations. If the compressor could not reproduce enough data in the version to reproduce the original. Alternatively, the algorithm may not be intelligent enough to discriminate between distortions of little subjective importance and those objectionable to the viewer. Compression artifacts occur in common media such as DVDs, common computer file formats such as JPEG, MP3, or MPEG files. Uncompressed media or losslessly compressed media do not suffer from compression artifacts, the minimization of perceivable artifacts is a key goal in implementing a lossy compression algorithm. However, artifacts are occasionally intentionally produced for artistic purposes, a known as glitch art or datamoshing. Technically speaking, an artifact is a particular class of data error that is usually the consequence of quantization in lossy data compression. Where transform coding is used, they assume the form of one of the basis functions of the coders transform space. When performing block-based coding for quantization, as in JPEG-compressed images, for example, the numbers 6 and 8 may get replaced. This has been observed to happen with JBIG2 in certain photocopier machines, at low bit rates, any lossy block-based coding scheme introduces visible artifacts in pixel blocks and at block boundaries. These boundaries can be transform block boundaries, prediction block boundaries, the term macroblocking is commonly used regardless of the artifacts cause. Other names include tiling, mosaicing, pixelating, quilting, block-artifacts are a result of the very principle of block transform coding. The transform is applied to a block of pixels, and to achieve lossy compression, the lower the bit rate, the more coarsely the coefficients are represented and the more coefficients are quantized to zero. Statistically, images have more low-frequency than high-frequency content, so it is the content that remains after quantization. Because this quantization process is applied individually in each block, neighboring blocks quantize coefficients differently and this leads to discontinuities at the block boundaries. These are most visible in areas, where there is little detail to mask the effect. Many photo editing programs, for instance, have proprietary JPEG artifact reduction algorithms built-in, consumer equipment often calls this post-processing MPEG Noise Reduction
37.
Gamma correction
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Gamma correction, or often simply gamma, is the name of a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. In the common case of A =1, inputs and outputs are typically in the range 0–1, Gamma encoding of floating-point images is not required, because the floating-point format already provides a piecewise linear approximation of a logarithmic curve. Although gamma encoding was developed originally to compensate for the characteristic of cathode ray tube displays. In CRT displays, the intensity varies nonlinearly with the electron-gun voltage. Altering the input signal by gamma compression can cancel this nonlinearity, the similarity of CRT physics to the inverse of gamma encoding needed for video transmission was a combination of luck and engineering, which simplified the electronics in early television sets. The concept of gamma can be applied to any nonlinear relationship, for a power-law curve, this slope is constant, but the idea can be extended to any type of curve, in which case gamma is defined as the slope of the curve in any particular region. For a given film formulation and processing method, this curve is its characteristic or Hurter–Driffield curve, since both axes use logarithmic units, the slope of the linear section of the curve is called the gamma of the film. Negative film typically has a less than 1, positive film typically has a gamma greater than 1. Photographic film has a greater ability to record fine differences in shade than can be reproduced on photographic paper. Similarly, most video screens are not capable of displaying the range of brightnesses that can be captured by typical electronic cameras, for this reason, considerable artistic effort is invested in choosing the reduced form in which the original image should be presented. The gamma correction, or contrast selection, is part of the repertoire used to adjust the reproduced image. Analogously, digital cameras record light using electronic sensors that usually respond linearly, in the process of rendering linear raw data to conventional RGB data, color space transformations and rendering transformations will be performed. In most computer systems, images are encoded with a gamma of about 0.45. A notable exception, until the release of Mac OS X10.6 in September 2009, were Macintosh computers, in any case, binary data in still image files are explicitly encoded, as are motion picture files. The system can optionally further manage both cases, through management, if a better match to the output device gamma is required. Below a compressed value of 0.04045 or a linear intensity of 0.00313, the dashed black curve behind the red curve is a standard γ =2.2 power-law curve, for comparison. For television signals, the actual values are defined by the video standards. A gamma characteristic is a relationship that approximates the relationship between the encoded luma in a television system and the actual desired image luminance
38.
Remote sensing
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Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation. It may be split into active remote sensing and passive remote sensing, passive sensors gather radiation that is emitted or reflected by the object or surrounding areas. Reflected sunlight is the most common source of radiation measured by passive sensors, examples of passive remote sensors include film photography, infrared, charge-coupled devices, and radiometers. Active collection, on the hand, emits energy in order to scan objects and areas whereupon a sensor then detects. RADAR and LiDAR are examples of remote sensing where the time delay between emission and return is measured, establishing the location, speed and direction of an object. Remote sensing makes it possible to data of dangerous or inaccessible areas. Remote sensing applications include monitoring deforestation in areas such as the Amazon Basin, glacial features in Arctic and Antarctic regions, military collection during the Cold War made use of stand-off collection of data about dangerous border areas. Remote sensing also replaces costly and slow data collection on the ground, the basis for multispectral collection and analysis is that of examined areas or objects that reflect or emit radiation that stand out from surrounding areas. For a summary of major remote sensing satellite systems see the overview table, conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Other types of active collection includes plasmas in the ionosphere, interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain. Laser and radar altimeters on satellites have provided a range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so, by measuring the height and wavelength of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions. Ultrasound and radar tide gauges measure sea level, tides and wave direction in coastal, light detection and ranging is well known in examples of weapon ranging, laser illuminated homing of projectiles. Vegetation remote sensing is an application of LIDAR. Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a range of frequencies. The most common are visible and infrared sensors, followed by microwave, gamma ray and rarely and they may also be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere. Simultaneous multi-spectral platforms such as Landsat have been in use since the 1970s and these thematic mappers take images in multiple wavelengths of electro-magnetic radiation and are usually found on Earth observation satellites, including the Landsat program or the IKONOS satellite. Landsat images are used by agencies such as KYDOW to indicate water quality parameters including Secchi depth, chlorophyll a density
39.
Sensor
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A sensor is always used with other electronics, whether as simple as a light or as complex as a computer. Moreover, analog sensors such as potentiometers and force-sensing resistors are still widely used, applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, robotics and many other aspects of our day-to-day life. A sensors sensitivity indicates how much the output changes when the input quantity being measured changes. For instance, if the mercury in a thermometer moves 1 cm when the changes by 1 °C. Some sensors can also affect what they measure, for instance, Sensors are usually designed to have a small effect on what is measured, making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a scale as microsensors using MEMS technology. In most cases, a microsensor reaches a higher speed. Most sensors have a transfer function. The sensitivity is defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is the slope of the transfer function. Converting the sensors electrical output to the measured units requires dividing the output by the slope. In addition, an offset is added or subtracted. For example -40 must be added to the output if 0 V output corresponds to -40 C input, for an analog sensor signal to be processed, or used in digital equipment, it needs to be converted to a digital signal, using an analog-to-digital converter. The full scale range defines the maximum and minimum values of the measured property, the sensitivity may in practice differ from the value specified. This is called a sensitivity error and this is an error in the slope of a linear transfer function. If the output differs from the correct value by a constant. This is an error in the y-intercept of a transfer function. Nonlinearity is deviation of a transfer function from a straight line transfer function
40.
Portable Network Graphics
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Portable Network Graphics is a raster graphics file format that supports lossless data compression. PNG was created as an improved, non-patented replacement for Graphics Interchange Format, PNG supports palette-based images, grayscale images, and full-color non-palette-based RGB/RGBA images. PNG was designed for transferring images on the Internet, not for professional-quality print graphics, a PNG file contains a single image in an extensible structure of chunks, encoding the basic pixels and other information such as textual comments and integrity checks. PNG files nearly always use file extension PNG or png and are assigned MIME media type image/png, PNG was approved for this use by the Internet Engineering Steering Group on 14 October 1996, and was published as an ISO/IEC standard in 2004. In this thread, Oliver Fromme, author of the popular DOS JPEG viewer QPEG, proposed the PING name, meaning PING is not GIF, although GIF allows for animation, it was decided that PNG should be a single-image format. In 2001, the developers of PNG published the Multiple-image Network Graphics format, MNG achieved moderate application support, but not enough among mainstream web browsers and no usage among web site designers or publishers. In 2008, certain Mozilla developers published the Animated Portable Network Graphics format with similar goals,1 October 1996, Version 1.0 of the PNG specification was released, and later appeared as RFC2083. It became a W3C Recommendation on 1 October 1996,31 December 1998, Version 1.1, with some small changes and the addition of three new chunks, was released. 11 August 1999, Version 1.2, adding one extra chunk, was released,10 November 2003, PNG became an International Standard. This version of PNG differs only slightly from version 1.2, the original PNG specification was authored by an ad-hoc group of computer graphics experts and enthusiasts. Discussions and decisions about the format were done exclusively via email, a chunk consists of four parts, length, chunk type/name, chunk data and CRC. The CRC is a network-byte-order CRC-32 computed over the type and chunk data. Chunk types are given a case sensitive ASCII type/name, compare FourCC. The case of the different letters in the name is a bit field that provides the decoder with some information on the nature of chunks it does not recognize, the case of the first letter indicates whether the chunk is critical or not. If the first letter is uppercase, the chunk is critical, if not, critical chunks contain information that is necessary to read the file. If a decoder encounters a critical chunk it does not recognize, the case of the second letter indicates whether the chunk is public or private. Uppercase is public and lowercase is private and this ensures that public and private chunk names can never conflict with each other. The third letter must be uppercase to conform to the PNG specification and it is reserved for future expansion
41.
Photographic filter
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In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. Sometimes they are used to make subtle changes to images. In monochrome photography coloured filters affect the brightness of different colours. Others change the balance of images, so that photographs under incandescent lighting show colours as they are perceived. There are filters that distort the image in a way, diffusing an otherwise sharp image, adding a starry effect. Linear and circular polarising filters reduce oblique reflections from non-metallic surfaces, many filters absorb part of the light available, necessitating longer exposure. As the filter is in the path, any imperfections—non-flat or non-parallel surfaces, reflections, scratches. There is no universal naming system for filters. The Wratten numbers adopted in the twentieth century by Kodak. Colour correction filters are often identified by a code of the form CC50Y—CC for colour correction,50 for the strength of the filter, photographic filters sell in larger quantities at correspondingly lower prices than many laboratory filters. The article on optical filters has material relevant to photographic filters, in digital photography the majority of filters used with film cameras have been rendered redundant by digital filters applied either in-camera or during post processing. Exceptions include the ultraviolet filter typically used to protect the front surface of the lens, the neutral density filter, the polarising filter, the only use of a clear filter is to protect the front of a lens. UV filters are used to block ultraviolet light, to which most photographic sensors. Normally, the glass or plastic of a lens is practically opaque to short-wavelength UV. A UV filter passes all or nearly all of the visible spectrum and it can be left on the lens for nearly all shots, UV filters are often used mainly for lens protection in the same way as clear filters. Strong UV filters are sometimes used for warming color photos taken in shade with daylight-type film. While in certain cases, such as harsh environments, a filter may be necessary. Arguments for the use of protection include, If the lens is dropped
42.
Luminance
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Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light passes through, is emitted or reflected from a particular area. The SI unit for luminance is candela per square metre, a non-SI term for the same unit is the nit. The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2, luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much power will be detected by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear, in this case, the solid angle of interest is the solid angle subtended by the eyes pupil. Luminance is used in the industry to characterize the brightness of displays. A typical computer display emits between 50 and 300 cd/m2, the sun has luminance of about 1. 6×109 cd/m2 at noon. Luminance is invariant in geometric optics and this means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the luminance is at most equal to the input. As an example, if one uses a lens to form an image that is smaller than the source object, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be brighter than the source, if light travels through a lossless medium, the luminance does not change along a given light ray. In the case of a perfectly diffuse reflector, the luminance is isotropic, then the relationship is simply L v = E v R / π A variety of units have been used for luminance, besides the candela per square metre. One candela per square metre is equal to, 10−4 stilbs π apostilbs π×10−4 lamberts 0.292 foot-lamberts Retinal damage can occur when the eye is exposed to high luminance, damage can occur due to local heating of the retina. Photochemical effects can cause damage, especially at short wavelengths. Also available in PDF form and Google Docs online version Autodesk Design Academy Measuring Light Levels
