Your eyes are far more sensitive to brightness than to color. JPEG and video exploit this by keeping full brightness detail but storing color at lower resolution — called chroma subsampling.

What the numbers mean

  • 4:4:4 — full color detail, no subsampling. Largest, sharpest.
  • 4:2:2 — color halved horizontally.
  • 4:2:0 — color halved both ways. The most common; cuts file size with loss most people never see.

When 4:2:0 hurts

Subsampling can blur sharp color edges — most visibly red or blue text on a contrasting background, where it gets a faint fuzzy halo. For screenshots of colored text, prefer PNG instead.

This is one reason photos compress so well as JPG but text doesn't. Related: JPEG quality and best format for screenshots.