Chrominance

Chrominance is the color information of an image signal, separated from luminance (brightness). In YUV or YCbCr color spaces, chrominance is carried by the U/Cb and V/Cr channels — Cb is the blue-yellow color difference, Cr is the red-cyan color difference — while Y carries luminance. This separation predates digital video, originating with NTSC and PAL analog broadcasting where it allowed black-and-white televisions to display color broadcasts (using only Y) while color sets used the chroma information. Modern digital video retains the YCbCr split because it enables chroma subsampling: since the human eye is less sensitive to color detail than to brightness, chroma channels can be stored at lower resolution (4:2:2 or 4:2:0) without obvious quality loss, drastically reducing file sizes. In post-production, chrominance matters for several operations: chroma key (separating subjects from green/blue backgrounds based on chroma values), chroma noise reduction (suppressing color noise separately from luminance noise), and chroma blur or sharpening (operations applied only to color information). Vectorscopes plot chrominance signals as scope-style displays showing color saturation and hue distribution. RGB color spaces have no separate chrominance — color and brightness are entangled in the three channel values. Reference: ITU-R BT.601 originally defined the YCbCr transformation used in subsequent broadcast standards.