A video display operates by displaying video images in response to a composite video signal received from a video source. The composite video signal comprises both luminance (luma) and chrominance (chroma) information. The luma portion contains the brightness, or black-and-white information for a given series of pixels, and the chroma portion contains the color information for the series of pixels. There are several standards for video signals commonly in use today, one being the National Television Standards Committee (NTSC), which is used in the United States and Japan. In NTSC, the chroma portion of a composite signal shifts in phase by one hundred eighty degrees between corresponding pixels on consecutive lines and frames. Another standard for video signals is Phase Alternating Lines (PAL), which is used in Europe. In PAL, the chroma component of the composite signal shifts in phase by approximately 270 degrees from line to line.
A number of functions in a video display rely on the accurate detection of motion within the signal, such as noise reduction and deinterlacing. Another application of motion detection is the separation of luma and chroma information within a signal. In some video transmission standards, chroma information within a composite video signal can be carried within the same frequency band as luma information. For example, in the NTSC standard, the chroma signal is added to the composite video signal by superimposing a sine wave onto the standard black and white (luma) signal. After the horizontal sync pulse, several cycles of the sine wave are added as a color burst. Following these cycles, a phase shift in the chrominance signal indicates the color to display. The amplitude of the signal determines the saturation.
The chroma signal is separated out of the composite video signal and decoded, along with the normal intensity signal, to determine the color content of the input signal. False color can be created when portions of the luma signal intrude into or near a frequency band associated with the chroma subcarrier. Dot crawl can occur when portions of the chroma signal intrude into the portion of the frequency band associated with the luma signal. The intruding signal can be mitigated with better accuracy by comb filtering the signal across three dimensions, but only if there is little or no motion in the video during this time. Accordingly, increasing the accuracy of motion detection across frames can allow for a significant reduction in color artifacts within a video signal.