Chroma Subsampling
A compression technique that records colour information at lower resolution than brightness information.
Formula / rule
4:4:4, 4:2:2, 4:2:0
Measured in
ratio
In depth
Human vision resolves luminance detail far better than colour detail, so halving or quartering the colour resolution saves substantial data with little visible cost on ordinary photographs. It becomes visible on saturated edges and on text, and it limits how far colour can be graded afterwards — which is why serious video capture aims for 4:2:2 or better.
Examples in practice
Red text on a blue background shows soft, bleeding edges at 4:2:0 that stay crisp at 4:4:4.