Entropy (information theory)
Information entropy is the average rate at which information is produced by a stochastic source of data. The measure of information entropy associated with each possible data value is the negative logarithm of the probability mass function for the value: S = − ∑ i P i log P i S=-\sum _P_\log; when the data source produces a low-probability value, the event carries more "information" than when the source data produces a high-probability value. The amount of information conveyed by each event defined in this way becomes a random variable whose expected value is the information entropy. Entropy refers to disorder or uncertainty, the definition of entropy used in information theory is directly analogous to the definition used in statistical thermodynamics; the concept of information entropy was introduced by Claude Shannon in his 1948 paper "A Mathematical Theory of Communication". The basic model of a data communication system is composed of three elements, a source of data, a communication channel, a receiver, – as expressed by Shannon – the "fundamental problem of communication" is for the receiver to be able to identify what data was generated by the source, based on the signal it receives through the channel.
The entropy provides an absolute limit on the shortest possible average length of a lossless compression encoding of the data produced by a source, if the entropy of the source is less than the channel capacity of the communication channel, the data generated by the source can be reliably communicated to the receiver. Information entropy is measured in bits or sometimes in "natural units" or decimal digits; the unit of the measurement depends on the base of the logarithm, used to define the entropy. The logarithm of the probability distribution is useful as a measure of entropy because it is additive for independent sources. For instance, the entropy of a fair coin toss is 1 bit, the entropy of m tosses is m bits. In a straightforward representation, log2 bits are needed to represent a variable that can take one of n values if n is a power of 2. If these values are probable, the entropy is equal to this number. If one of the values is more probable to occur than the others, an observation that this value occurs is less informative than if some less common outcome had occurred.
Conversely, rarer events provide more information. Since observation of less probable events occurs more the net effect is that the entropy received from non-uniformly distributed data is always less than or equal to log2. Entropy is zero; the entropy quantifies these considerations when a probability distribution of the source data is known. The meaning of the events observed. Entropy only takes into account the probability of observing a specific event, so the information it encapsulates is information about the underlying probability distribution, not the meaning of the events themselves; the basic idea of information theory is that the more one knows about a topic, the less new information one is apt to get about it. If an event is probable, it is no surprise when it happens and provides little new information. Inversely, if the event was improbable, it is much more informative; the information content is an increasing function of the reciprocal of the probability of the event. If more events may happen, entropy measures the average information content you can expect to get if one of the events happens.
This implies that casting a die has more entropy than tossing a coin because each outcome of the die has smaller probability than each outcome of the coin. Entropy is a measure of unpredictability of the state, or equivalently, of its average information content. To get an intuitive understanding of these terms, consider the example of a political poll; such polls happen because the outcome of the poll is not known. In other words, the outcome of the poll is unpredictable, performing the poll and learning the results gives some new information. Now, consider the case that the same poll is performed a second time shortly after the first poll. Since the result of the first poll is known, the outcome of the second poll can be predicted well and the results should not contain much new information. Consider the example of a coin toss. Assuming the probability of heads is the same as the probability of tails the entropy of the coin toss is as high as it could be. There is no way to predict the outcome of the coin toss ahead of time: if one has to choose, the best one can do is predict that the coin will come up heads, this prediction will be correct with probability 1/2.
Such a coin toss has one bit of entropy since there are two possible outcomes that occur with equal probability, learning the actual outcome contains one bit of information. In contrast, a coin toss using a coin that has two heads and no tails has zero entropy since the coin will always come up heads, the outcome can be predicted pe
In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storing and transmitting content; the different versions of the photo of the cat to the right show how higher degrees of approximation create coarser images as more details are removed. This is opposed to lossless data compression; the amount of data reduction possible using lossy compression is much higher than through lossless techniques. Well-designed lossy compression technology reduces file sizes before degradation is noticed by the end-user; when noticeable by the user, further data reduction may be desirable. Lossy compression is most used to compress multimedia data in applications such as streaming media and internet telephony. By contrast, lossless compression is required for text and data files, such as bank records and text articles, it can be advantageous to make a master lossless file which can be used to produce additional copies from.
This allows one to avoid basing new compressed copies off of a lossy source file, which would yield additional artifacts and further unnecessary information loss. It is possible to compress many types of digital data in a way that reduces the size of a computer file needed to store it, or the bandwidth needed to transmit it, with no loss of the full information contained in the original file. A picture, for example, is converted to a digital file by considering it to be an array of dots and specifying the color and brightness of each dot. If the picture contains an area of the same color, it can be compressed without loss by saying "200 red dots" instead of "red dot, red dot...... red dot." The original data contains a certain amount of information, there is a lower limit to the size of file that can carry all the information. Basic information theory says; when data is compressed, its entropy increases, it cannot increase indefinitely. As an intuitive example, most people know that a compressed ZIP file is smaller than the original file, but compressing the same file will not reduce the size to nothing.
Most compression algorithms can recognize when further compression would be pointless and would in fact increase the size of the data. In many cases, files or data streams contain more information than is needed for a particular purpose. For example, a picture may have more detail than the eye can distinguish when reproduced at the largest size intended. Developing lossy compression techniques as matched to human perception as possible is a complex task. Sometimes the ideal is a file that provides the same perception as the original, with as much digital information as possible removed; the terms'irreversible' and'reversible' are preferred over'lossy' and'lossless' for some applications, such as medical image compression, to circumvent the negative implications of'loss'. The type and amount of loss can affect the utility of the images. Artifacts or undesirable effects of compression may be discernible yet the result still useful for the intended purpose. Or lossy compressed images may be'visually lossless', or in the case of medical images, so-called Diagnostically Acceptable Irreversible Compression may have been applied.
More some forms of lossy compression can be thought of as an application of transform coding – in the case of multimedia data, perceptual coding: it transforms the raw data to a domain that more reflects the information content. For example, rather than expressing a sound file as the amplitude levels over time, one may express it as the frequency spectrum over time, which corresponds more to human audio perception. While data reduction is a main goal of transform coding, it allows other goals: one may represent data more for the original amount of space – for example, in principle, if one starts with an analog or high-resolution digital master, an MP3 file of a given size should provide a better representation than a raw uncompressed audio in WAV or AIFF file of the same size; this is because uncompressed audio can only reduce file size by lowering bit rate or depth, whereas compressing audio can reduce size while maintaining bit rate and depth. This compression becomes a selective loss of the least significant data, rather than losing data across the board.
Further, a transform coding may provide a better domain for manipulating or otherwise editing the data – for example, equalization of audio is most expressed in the frequency domain rather than in the raw time domain. From this point of view, perceptual encoding is not about discarding data, but rather about a better representation of data. Another use is for backward compatibility and graceful degradation: in color television, encoding color via a luminance-chrominance transform domain means that black-and-white sets display the luminance, while ignoring the color information. Another example is chroma subsampling: the use of color spaces such as YIQ, used in NTSC, allow one to reduce the resolution on the components to accord with human perception – humans have highest resolution for black-an
1080i is an abbreviation referring to a combination of frame resolution and scan type, used in high-definition television and high-definition video. The number "1080" refers to the number of horizontal lines on the screen; the "i" is an abbreviation for "interlaced". A related display resolution is 1080p, which has 1080 lines of resolution; the term assumes a widescreen aspect ratio of 16:9, so the 1080 lines of vertical resolution implies 1920 columns of horizontal resolution, or 1920 pixels × 1080 lines. A 1920 pixels × 1080 lines screen has a total of 2.1 megapixels and a temporal resolution of 50 or 60 interlaced fields per second. This format is used in the SMPTE 292M standard; the choice of 1080 lines originates with Charles Poynton, who in the early 1990s pushed for "square pixels" to be used in HD video formats. Within the designation "1080i", the i stands for interlaced scan. A frame of 1080i video consists of two sequential fields of 540 vertical pixels; the first field consists of all odd-numbered TV lines and the second all numbered lines.
The horizontal lines of pixels in each field are captured and displayed with a one-line vertical gap between them, so the lines of the next field can be interlaced between them, resulting in 1080 total lines. 1080i differs from 1080p, where the p stands for progressive scan, where all lines in a frame are captured at the same time. In native or pure 1080i, the two fields of a frame correspond to different instants, so motion portrayal is good; this is true for interlaced video in general and can be observed in still images taken of fast motion scenes. However, when 1080p material is captured at 25 or 30 frames/second, it is converted to 1080i at 50 or 60 fields/second for processing or broadcasting. In this situation both fields in a frame do correspond to the same instant; the field-to-instant relation is somewhat more complex for the case of 1080p at 24 frames/second converted to 1080i at 60 fields/second. The field rate of 1080i is 60 Hz for countries that use or used System M as analog television system with 60 fields/sec, or 50 Hz for regions that use or used 625-lines television system with 50 fields/sec.
Both field rates can be carried by major digital television broadcast formats such as ATSC, DVB, ISDB-T International. The frame rate can be implied by the context, while the field rate is specified after the letter i, such as "1080i60". In this case 1080i60 refers to 60 fields per second; the European Broadcasting Union prefers to use the resolution and frame rate separated by a slash, as in 1080i/30 and 1080i/25 480i/30 and 576i/25. Resolutions of 1080i60 or 1080i50 refers to 1080i/30 or 1080i/25 in EBU notation. 1080i is directly compatible with some CRT HDTVs on which it can be displayed natively in interlaced form, but for display on progressive-scan—e.g. Most new LCD and plasma TVs, it must be deinterlaced. Depending on the television's video processing capabilities, the resulting video quality may vary, but may not suffer. For example, film material at 25fps may be deinterlaced from 1080i50 to restore a full 1080p resolution at the original frame rate without any loss. Preferably video material with 50 or 60 motion phases/second is to be converted to 50p or 60p before display.
Worldwide, most HD channels on satellite and cable broadcast in 1080i. In the United States, 1080i is the preferred format for most broadcasters, with Inc.. Viacom, AT&T, Comcast owned networks broadcasting in the format. Only Fox-owned television networks and Disney-owned television networks, along with MLB Network and a few other cable networks use 720p as the preferred format for their networks. Many ABC affiliates owned by Hearst Television and former Belo Corporation stations owned by TEGNA, along with some individual affiliates of those three networks, air their signals in 1080i and upscale network programming for master control and transmission purposes, as most syndicated programming and advertising is produced and distributed in 1080i, removing a downscaling step to 720p; this allows local newscasts on these ABC affiliates to be produced in the higher resolution to match the picture quality of their 1080i competitors. Some cameras and broadcast systems that use 1080 vertical lines per frame do not use the full 1920 pixels of a nominal 1080i picture for image capture and encoding.
Common subsampling ratios include 3/4 and 1/2. Where used, the lower horizontal resolution is scaled to capture and/or display a full-sized picture. Using half horizontal resolution and only one field of each frame results in the format known as qHD, which has fram
Sony Corporation is a Japanese multinational conglomerate corporation headquartered in Kōnan, Tokyo. Its diversified business includes consumer and professional electronics, gaming and financial services; the company owns the largest music entertainment business in the world, the largest video game console business and one of the largest video game publishing businesses, is one of the leading manufacturers of electronic products for the consumer and professional markets, a leading player in the film and television entertainment industry. Sony was ranked 97th on the 2018 Fortune Global 500 list. Sony Corporation is the electronics business unit and the parent company of the Sony Group, engaged in business through its four operating components: electronics, motion pictures and financial services; these make Sony one of the most comprehensive entertainment companies in the world. The group consists of Sony Corporation, Sony Pictures, Sony Mobile, Sony Interactive Entertainment, Sony Music, Sony/ATV Music Publishing, Sony Financial Holdings, others.
Sony is among the semiconductor sales leaders and since 2015, the fifth-largest television manufacturer in the world after Samsung Electronics, LG Electronics, TCL and Hisense. The company's current slogan is Be Moved, their former slogans were The One and Only, It's like.no.other and make.believe. Sony has a weak tie to the Sumitomo Mitsui Financial Group corporate group, the successor to the Mitsui group. Sony began in the wake of World War II. In 1946, Masaru Ibuka started an electronics shop in a department store building in Tokyo; the company started with a total of eight employees. In May 1946, Ibuka was joined by Akio Morita to establish a company called Tokyo Tsushin Kogyo; the company built Japan's first tape recorder, called the Type-G. In 1958, the company changed its name to "Sony"; when Tokyo Tsushin Kogyo was looking for a romanized name to use to market themselves, they considered using their initials, TTK. The primary reason they did not is that the railway company Tokyo Kyuko was known as TTK.
The company used the acronym "Totsuko" in Japan, but during his visit to the United States, Morita discovered that Americans had trouble pronouncing that name. Another early name, tried out for a while was "Tokyo Teletech" until Akio Morita discovered that there was an American company using Teletech as a brand name; the name "Sony" was chosen for the brand as a mix of two words: one was the Latin word "sonus", the root of sonic and sound, the other was "sonny", a common slang term used in 1950s America to call a young boy. In 1950s Japan, "sonny boys" was a loan word in Japanese, which connoted smart and presentable young men, which Sony founders Akio Morita and Masaru Ibuka considered themselves to be; the first Sony-branded product, the TR-55 transistor radio, appeared in 1955 but the company name did not change to Sony until January 1958. At the time of the change, it was unusual for a Japanese company to use Roman letters to spell its name instead of writing it in kanji; the move was not without opposition: TTK's principal bank at the time, had strong feelings about the name.
They pushed for a name such as Sony Teletech. Akio Morita was firm, however. Both Ibuka and Mitsui Bank's chairman gave their approval. According to Schiffer, Sony's TR-63 radio "cracked open the U. S. market and launched the new industry of consumer microelectronics." By the mid-1950s, American teens had begun buying portable transistor radios in huge numbers, helping to propel the fledgling industry from an estimated 100,000 units in 1955 to 5 million units by the end of 1968. Sony co-founder Akio Morita founded Sony Corporation of America in 1960. In the process, he was struck by the mobility of employees between American companies, unheard of in Japan at that time; when he returned to Japan, he encouraged experienced, middle-aged employees of other companies to reevaluate their careers and consider joining Sony. The company filled many positions in this manner, inspired other Japanese companies to do the same. Moreover, Sony played a major role in the development of Japan as a powerful exporter during the 1960s, 1970s and 1980s.
It helped to improve American perceptions of "made in Japan" products. Known for its production quality, Sony was able to charge above-market prices for its consumer electronics and resisted lowering prices. In 1971, Masaru Ibuka handed the position of president over to his co-founder Akio Morita. Sony began a life insurance company in one of its many peripheral businesses. Amid a global recession in the early 1980s, electronics sales dropped and the company was forced to cut prices. Sony's profits fell sharply. "It's over for Sony," one analyst concluded. "The company's best days are behind it." Around that time, Norio Ohga took up the role of president. He encouraged the development of the Compact Disc in the 1970s and 1980s, of the PlayStation in the early 1990s. Ohga went on to purchase CBS Records in 1988 and Columbia Pictures in 1989 expanding Sony's media presence. Ohga would succeed Morita as chief executive officer in 1989. Under the vision of co-founder Akio Morita and his successors, the company had aggressively expanded in
JPEG is a used method of lossy compression for digital images for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG achieves 10:1 compression with little perceptible loss in image quality. JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; these format variations are not distinguished, are called JPEG. The term "JPEG" is an initialism/acronym for the Joint Photographic Experts Group, which created the standard; the MIME media type for JPEG is image/jpeg, except in older Internet Explorer versions, which provides a MIME type of image/pjpeg when uploading JPEG images. JPEG files have a filename extension of.jpg or.jpeg. JPEG/JFIF supports a maximum image size of 65,535×65,535 pixels, hence up to 4 gigapixels for an aspect ratio of 1:1. "JPEG" stands for Joint Photographic Experts Group, the name of the committee that created the JPEG standard and other still picture coding standards.
The "Joint" stood for ISO TC97 WG8 and CCITT SGVIII. In 1987, ISO TC 97 became ISO/IEC JTC1 and, in 1992, CCITT became ITU-T. On the JTC1 side, JPEG is one of two sub-groups of ISO/IEC Joint Technical Committee 1, Subcommittee 29, Working Group 1 – titled as Coding of still pictures. On the ITU-T side, ITU-T SG16 is the respective body; the original JPEG Group was organized in 1986, issuing the first JPEG standard in 1992, approved in September 1992 as ITU-T Recommendation T.81 and, in 1994, as ISO/IEC 10918-1. The JPEG standard specifies the codec, which defines how an image is compressed into a stream of bytes and decompressed back into an image, but not the file format used to contain that stream; the Exif and JFIF standards define the used file formats for interchange of JPEG-compressed images. JPEG standards are formally named as Information technology – Digital compression and coding of continuous-tone still images. ISO/IEC 10918 consists of the following parts: Ecma International TR/98 specifies the JPEG File Interchange Format.
The JPEG compression algorithm operates at its best on photographs and paintings of realistic scenes with smooth variations of tone and color. For web usage, where reducing the amount of data used for an image is important for responsive presentation, JPEG's compression benefits make JPEG popular. JPEG/Exif is the most common format saved by digital cameras. However, JPEG is not well suited for line drawings and other textual or iconic graphics, where the sharp contrasts between adjacent pixels can cause noticeable artifacts; such images are better saved in a lossless graphics format such as TIFF, GIF, PNG, or a raw image format. The JPEG standard includes a lossless coding mode; as the typical use of JPEG is a lossy compression method, which reduces the image fidelity, it is inappropriate for exact reproduction of imaging data. JPEG is not well suited to files that will undergo multiple edits, as some image quality is lost each time the image is recompressed if the image is cropped or shifted, or if encoding parameters are changed – see digital generation loss for details.
To prevent image information loss during sequential and repetitive editing, the first edit can be saved in a lossless format, subsequently edited in that format finally published as JPEG for distribution. JPEG uses a lossy form of compression based on the discrete cosine transform; this mathematical operation converts each frame/field of the video source from the spatial domain into the frequency domain. A perceptual model based loosely on the human psychovisual system discards high-frequency information, i.e. sharp transitions in intensity, color hue. In the transform domain, the process of reducing information is called quantization. In simpler terms, quantization is a method for optimally reducing a large number scale into a smaller one, the transform-domain is a convenient representation of the image because the high-frequency coefficients, which contribute less to the overall picture than other coefficients, are characteristically small-values with high compressibility; the quantized coefficients are sequenced and losslessly packed into the output bitstream.
Nearly all software implementations of JPEG permit user control over the compression ratio, allowing the user to trade off picture-quality for smaller file size. In embedded applications, the parameters are fixed for the application; the compression method is lossy, meaning that some original image information is lost and cannot be restored affecting image quality. There is an optional lossless mode defined in the JPEG standard. However, this mode is not supported in products. There is an interlaced progressive JPEG format, in which data is compressed in multiple passes of progressively higher detail; this is ideal for large images that will be displayed while downloading over a slow connection, allowing a reasonable preview after receiving only a portion of the data. However, support for progressive JPEGs is not universal; when progressive JPEGs are received by programs that do not support them (such