Chroma Subsampling — 4:4:4, 4:2:2, and 4:2:0

Chroma Subsampling

For HDMI bandwidth and version requirements, see signal-types/hdmi. For HDR and color gamut, see glossary/hdr.

Chroma subsampling is a video compression technique that reduces the color (chroma) information in a video signal relative to the luminance (brightness) information. Human vision is far more sensitive to brightness differences than color differences, so reducing chroma resolution causes minimal perceived quality loss while significantly reducing bandwidth. In AV systems, chroma subsampling determines whether a 4K60 signal can be transmitted over HDMI 2.0 (which has limited bandwidth) and whether color accuracy is maintained for professional video or graphics applications.

How It Works

A digital video signal consists of one luminance channel (Y) and two color-difference channels (Cb and Cr, also called U and V). The notation J:a:b describes how chroma is sampled relative to luminance in a 2-row, 4-pixel reference block:

• J: always 4 — the number of luminance samples per block reference width
• a: number of Cb/Cr samples in the first row
• b: number of Cb/Cr samples in the second row (0 means same as first row for Cb/Cr, full for both)

4:4:4 — Full Color

Every pixel has its own luminance and both chroma values. No color information is discarded. Required for:

• Professional color grading and post-production
• Chroma keying (green screen) — subsampled chroma produces poor key edges
• Text rendering on PC-connected displays (subchromatic sampling of text causes color fringing on fine edges)
• Medical, scientific, and broadcast quality reference monitoring

4K60 4:4:4 requires ~18 Gbps — beyond HDMI 2.0's 18 Gbps theoretical limit (actual overhead means it requires HDMI 2.1 in practice).

4:2:2 — Horizontal Chroma Halved

Chroma is sampled at half the horizontal resolution. Every two pixels share one pair of Cb/Cr values. Bandwidth is reduced by ~33% vs 4:4:4. Used in:

• Professional broadcast cameras (Sony, Panasonic, Canon cinema cameras)
• Blackmagic Design cameras and recorders
• Broadcast SDI signals

4K60 4:2:2 requires ~12 Gbps — fits within HDMI 2.0 with some overhead margin.

4:2:0 — Both Horizontal and Vertical Chroma Halved

Chroma is sampled at half both horizontal and vertical resolution. Every four pixels (2×2 block) share one Cb/Cr value. Bandwidth is reduced by ~50% vs 4:4:4. This is the format used by:

• All consumer streaming video (Netflix, YouTube, Blu-ray)
• Consumer displays (nearly all 4K TVs receive 4:2:0)
• HDMI 2.0 for 4K60 — at 4:2:0, 4K60 requires only ~12 Gbps, fitting within HDMI 2.0's bandwidth

4K30 at 4:4:4 and 4K60 at 4:2:0 both fit within HDMI 2.0. 4K60 at 4:4:4 requires HDMI 2.1.

Bandwidth Summary

Relevance to AV System Design

Conference rooms: sources (laptops, codecs) typically output 4:2:0 or 4:2:2 for 4K. Consumer displays are optimized for 4:2:0. For most presentation and conferencing applications, 4:2:0 is entirely acceptable.

Graphics and text: PC sources connecting to displays should ideally output 4:4:4 to avoid color fringing on text. Most PC GPUs default to 4:4:4 on HDMI connections to PC monitors. Ensure the display and cable support 4:4:4 at the selected resolution and frame rate.

Production and broadcast: use 4:2:2 or 4:4:4. SDI naturally carries 4:2:2. Any signal chain involving chroma keying must maintain 4:2:2 at minimum.

Common Pitfalls

• 4K60 signal not passing through HDMI 2.0 switcher. Source outputs 4K60 4:4:4; the HDMI 2.0 switcher's bandwidth limit prevents this signal from passing. Fix: configure the source to output 4K60 4:2:0 (which fits HDMI 2.0) or upgrade to HDMI 2.1-capable switcher hardware.

• Assuming all 4K signals are equivalent. A 4K30 4:4:4 signal and a 4K60 4:2:0 signal have very similar bandwidth requirements but very different quality characteristics. For graphics and text, 4:4:4 at lower frame rate is preferable; for motion video, higher frame rate 4:2:0 is often better.

• HDMI extender misreporting chroma capability. Some HDBaseT extenders advertise 4K60 support but only at 4:2:0; connecting a source set to 4:4:4 at 4K60 produces no signal. Fix: verify the exact chroma subsampling the extender supports at each resolution; set the source to match.