Glossary
Chroma Subsampling
Also: 4:2:0 · 4:4:4 · chroma subsampling
Chroma subsampling shrinks files by storing colour at lower resolution than brightness, exploiting the eye's weaker sensitivity to colour detail. JPG and WebP use it, written as 4:4:4, 4:2:2, or 4:2:0.
Reviewed by Chad Solomon · Updated June 2026
Explained
How chroma subsampling works
Chroma subsampling splits an image into brightness (luma) and colour (chroma), then keeps full-resolution brightness while halving or quartering colour resolution. The eye notices brightness detail far more than colour detail, so the saving is largely invisible on photographs.
Explained
Reading the ratios
Three ratios are common: 4:4:4 keeps full colour (no subsampling), 4:2:2 halves colour horizontally, and 4:2:0 halves it both ways — the smallest, used by most JPGs. 4:2:0 can blur sharp coloured edges and red text, so graphics and screenshots are better kept lossless.
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Questions
Frequently asked
- What does 4:2:0 mean?
- 4:2:0 chroma subsampling stores colour at one-quarter the resolution of brightness. It produces the smallest JPG files and is nearly invisible on photos, but can blur sharp coloured edges.
- Why does red text look blurry in JPG?
- JPG's 4:2:0 chroma subsampling lowers colour resolution, smearing high-contrast coloured edges like red text. Save such images as PNG or WebP lossless instead.
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