4:2:2

4:2:2 is an expression of chroma subsampling, a practice of encoding images by compressing their color information in order to reduce the overall storage size and bitrate of video files.

The 4:2:2 chroma subsampling takes two pixels from both the top 'a' and bottom 'b' rows. This reduces the chroma information to 50 percent of the uncompressed source chroma. The two chroma components are sampled at half the sample rate of luma, i.e. the horizontal chroma resolution is halved. This reduces the bandwidth of an uncompressed video signal by one-third with little to no visual difference.

Many high-end digital video formats and interfaces use this scheme - 4:2:2 is one of the more popular chroma subsampling used in producing high-quality video.