Chroma subsampling reduces video bandwidth by storing color detail at lower resolution than brightness detail. The human eye is far more sensitive to luma (brightness) than to chroma (color), so throwing away some color information is often invisible — but not always. The notation 4:x:y describes how much color is kept relative to brightness.
Reading the notation
The three numbers describe a 4-pixel-wide, 2-pixel-tall sample region:
- First number (4) — luma sampling width (always 4, the reference).
- Second number — how many chroma samples across the top row.
- Third number — how many chroma samples across the bottom row (0 = same as top row).
| Format | Color detail | Relative bandwidth | Typical use |
|---|---|---|---|
| 4:4:4 | Full | 100% | PC/text, graphics, mastering |
| 4:2:2 | Half horizontal | ~67% | Broadcast, pro capture |
| 4:2:0 | Half horizontal + vertical | ~50% | Streaming, Blu-ray, HDMI HDR |
Why it matters in AV
Chroma is where systems buy back bandwidth when a link can’t carry full color:
- 4K60 over HDMI 2.0 (18 Gbps) can’t do 4:4:4 10-bit. Sources drop to 4:2:2 or 4:2:0 to fit — fine for video, but see the text warning below.
- HDR almost always ships as 4:2:0 or 4:2:2 because 10-bit color needs the extra headroom.
- AV-over-IP and codecs often encode in 4:2:0 by default to cut bitrate.
When the difference is visible
- Text and fine graphics. 4:2:0/4:2:2 causes colored fringing and blur on small text and sharp color edges — a real problem for computer/desktop content and signage, which is why PC sources should run 4:4:4 whenever the link allows.
- Full-motion video. For camera and film content, 4:2:0 is usually indistinguishable from 4:4:4 at normal viewing distance — which is why it’s the streaming/broadcast default.
Rule of thumb
Match sampling to content: 4:4:4 for anything with text or sharp graphics, and accept 4:2:0 for motion video when bandwidth is tight. If a display shows fuzzy or fringed text, suspect the source or a link dropping to reduced chroma — check the resolution/color-depth setting and the cable’s rating.
Related
Sources
- ITU-R BT.709 and ITU-R BT.2020 — luma/chroma encoding and colour subsampling for HD and UHD.
- ANSI/CTA-861 — video format and colorimetry signaling (including 4:4:4 / 4:2:2 / 4:2:0) over HDMI.