Chroma Subsampling

• Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information.
  • It is used in many video encoding schemes both analog and digital and also in JPEG encoding. Because of storage and transmission limitations, compression of signals is desirable.
  • Since the human visual system is much more sensitive to variations in brightness than color, a video system can be optimized by devoting more bandwidth to the luma component Y’ than to color components Cb and Cr.
  • No visual degradation of video quality, if we drop Chroma .i.e. color information. E.g. 4:2:2 Y’CbCr scheme requires two-thirds the bandwidth of 4:4:4 R’G’B’. This reduction results in almost no visual difference to the viewer.

Types of subsampling:

• 4:4:4 indicates no subsampling. No Compression and highest quality video.

• 4:2:2 indicates horizontal subsampling of Cb and Cr with factor 2 Many high-end digital video formats and interfaces use this scheme.

• 4:1:1 indicates horizontal subsampling of Cb and Cr with factor 4 This scheme is not considered to be broadcast quality and was only acceptable for low-end and consumer applications.

• 4:2:0 indicates horizontal and vertical subsampling of Cb and Cr with factor 2 respectively. This scheme is generally used in JPEG and MPEG. Maximum compression but poor video quality.

Diagram: