Y'CbCr is the color space originally defined by BT.601, and now used for all digital component video formats. Y' is the luma component and the Cb and Cr components are color difference signals. The technically correct notation is Y'Cb'Cr' since all three components are derived from R'G'B'. Many people use the YCbCr notation rather than Y'CbCr or Y'Cb'Cr'.

4:4:4 Y'CbCr means that for every Y' sample, there is one sample each of Cb and Cr.

4:2:2 Y'CbCr means that for every two horizontal Y' samples, there is one sample each of Cb and Cr.

4:1:1 Y'CbCr means that for every four horizontal Y' samples, there is one sample each of Cb and Cr.

4:2:0 Y'CbCr means that for every block of 2 x 2 Y' samples, there is one sample each of Cb and Cr. There are three variations of 4:2:0 YCbCr, with the difference being the position of Cb and Cr sampling relative to Y.

Note that the coefficients to convert R'G'B' to Y'CbCr are different for SDTV and HDTV applications.

This definition is in context to Multimedia. See more contextual defintions for Y'CbCr, YCbCr.