The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous rotational or other cyclic motion is represented by a series of short or instantaneous samples at a sampling rate close to the period of the motion. It accounts for the "wagon-wheel effect", so-called because in video, spoked wheels sometimes appear to be turning backwards.
Figure 1: Stroboscopic effect resulting from a moving screwdriver lit with a square-waveform modulated light source with a modulation frequency of 100 Hz, duty cycle of 50 % and 100 % modulation (SVM = 4,9); small photo inset shows absence of stroboscopic effect if screwdriver is not moved
Figure 2: Stroboscopic effect contrast threshold function (see Visibility)
Figure 3: Generic setup to test lighting equipment for its stroboscopic effect performance
In signal processing and related disciplines, aliasing is the overlapping of frequency components resulting from a sample rate below the Nyquist rate. This overlap results in distortion or artifacts when the signal is reconstructed from samples which causes the reconstructed signal to differ from the original continuous signal.
Aliasing that occurs in signals sampled in time, for instance in digital audio or the stroboscopic effect, is referred to as temporal aliasing. Aliasing in spatially sampled signals is referred to as spatial aliasing.
This full-sized image shows what a properly sampled image of a brick wall should look like with a screen of sufficient resolution.
When the resolution is reduced, aliasing appears in the form of a moiré pattern.
