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Glossary of Audio and Video Terms

YUV, also known as Y'CbCr and YPbPr, is a color space in which the Y stands for the luminance component (the brightness) and U and V are chrominance (color difference) components. It is commonly used in video applications, where it is also referred to as component video.

The advantage of a YUV signal is that it can be easily manipulated to deliberately discard some information in order to reduce bandwidth. The Human Visual System (HVS) has fairly low color resolution, the high-resolution color images we see are processed by the visual system by combining the high-resolution black and white image with the low-resolution color image. Using this information it is possible to reduce the amount of signal in the U and V considerably, leaving the eye to recombine them.

YUV images can be sampled in several different ways, including (in order of decreasing quality):

• YUV 4:4:4
• YUV 4:2:2
• YUV 4:2:0
• YUV 4:1:1
• YUV 4:1:0

The numbers reflect the relative importance given to each channel: the first number gives the relative amount of Y information on each line, the second the relative amount of U and V information on each even-numbered line, the third number the same for odd-numbered lines.

For example, YUV 4:2:2 has an amount of information in the Y channel double each of the U and V channels; YUV 4:2:0 has the Y channel four times the amount of information of the other two channels, because U and V information is omitted on odd-numbered lines. During display, the missing U and V information is approximated by interpolation from those values that are present.

3ivx uses YUV 4:2:0 as its native color space. YUV 4:2:0 is used because the human eye is much better at seeing differences in brightness than in color.

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