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Chroma subsampling
In image processing, chroma subsampling is the use of lower resolution for the colour (chroma) information in an image than for the brightness (intensity or luma) information.
Because the human eye is less sensitive to colour than intensity, the chroma components of an image need not be as well defined as the luma component, so many video systems sample the colour at a lower definition than the brightness. This reduces the overall bandwidth of the video signal without apparent loss of picture quality.
The subsampling in a video system is usually expressed as a three part ratio. The three terms of the ratio are: the number of luma pixels in a complete sample area, the number of chroma pixels in odd lines, and the number of chroma pixels in even lines:
Common Chroma subsampling ratios include:
- 4:2:0 DVD, DV (PAL)
- 4:1:1 D-7, DV (NTSC), DVC pro 25
- 4:2:2 D-9, Digital Betacam, DVC Pro 50
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