Glossary
Chroma Subsampling
Also: 4:2:0 · 4:4:4 · chroma subsampling
Chroma subsampling shrinks files by storing color at lower resolution than brightness, exploiting the eye's weaker sensitivity to color 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 color (chroma), then keeps full-resolution brightness while halving or quartering color resolution. The eye notices brightness detail far more than color detail, so the saving is largely invisible on photographs.
Explained
Reading the ratios
Three ratios are common: 4:4:4 keeps full color (no subsampling), 4:2:2 halves color horizontally, and 4:2:0 halves it both ways — the smallest, used by most JPGs. 4:2:0 can blur sharp colored 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 color at one-quarter the resolution of brightness. It produces the smallest JPG files and is nearly invisible on photos, but can blur sharp colored edges.
- Why does red text look blurry in JPG?
- JPG's 4:2:0 chroma subsampling lowers color resolution, smearing high-contrast colored edges like red text. Save such images as PNG or WebP lossless instead.
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