chromasubsampling

Chroma subsampling is a technique used in color image and video compression to reduce the amount of color information that must be stored or transmitted. It works by lowering the resolution of the chrominance components while preserving most of the luminance (brightness) information. In common color spaces such as YCbCr, an image is separated into a luminance component (Y) and two chrominance components (Cb and Cr). Because the human eye is more sensitive to brightness details than to fine color detail, chroma data can be sampled at a lower rate with limited perceived impact on image quality. The result is lower bandwidth or storage requirements for a given visual quality.

Chroma subsampling schemes describe how often chroma samples are taken relative to luminance. The most common formats are 4:4:4 (no subsampling), 4:2:2 (half horizontal chroma resolution), 4:2:0 (half horizontal and half vertical chroma resolution), and 4:1:1 (reduced horizontal chroma). In each case the first number refers to luminance sampling, while the second and third numbers indicate the sampling rate of the Cb and Cr components. For example, 4:2:0 stores chroma information at one quarter the resolution of the luma in both directions.

Applications and impact: Chroma subsampling is widely used in digital video, broadcasting, and streaming. Formats such as MPEG-2, H.264, and H.265 commonly employ 4:2:0, balancing efficiency and perceived quality. Higher-quality situations, such as professional video or color-critical work, may use 4:2:2 or 4:4:4. Subsampling can introduce color-related artifacts, especially when heavy upsampling is required or in high-frequency color transitions, but is generally well-tolerated due to the limited human sensitivity to color detail.