Chroma subsampling (4:2:0)
Also known as: 4:2:0, 4:2:2, 4:4:4, chroma subsampling meaning
Chroma subsampling saves space by storing full brightness detail but fewer color samples, exploiting the fact that human eyes notice brightness more than color. Notations like 4:2:0, 4:2:2, and 4:4:4 describe how much color information is kept — 4:2:0 keeps the least and is the most common.
- Full brightness, reduced color sampling
- 4:2:0 keeps the least color and is most common
- Saves space with little visible quality loss
Why eyes let video drop color detail
Video separates each pixel into luma (brightness) and chroma (color). The human eye is far more sensitive to brightness, so encoders keep luma at full resolution while sampling chroma less often, with little visible loss in normal viewing.
The ratios describe the sampling: 4:4:4 keeps full color, 4:2:2 keeps roughly half the horizontal color detail, and 4:2:0 keeps about a quarter by halving color both horizontally and vertically. Most consumer video, streaming, and phone recording use 4:2:0.
Where it helps and where it hurts
For ordinary footage, 4:2:0 noticeably reduces data with no obvious quality drop, which is why it is the default for efficient delivery and smaller files. Higher sampling like 4:2:2 or 4:4:4 keeps more color for professional grading and chroma-key work, at the cost of larger files.
Subsampling can show its limits on fine colored edges, thin text, or heavy color correction, where reduced chroma may look soft or blocky.