a) When television was monochrome and sensors were in approximate conformance to CIE Photopic Spectral Luminous Efficiency Function, it became common to think of the video signal as the luminance signal. With the introduction of color, a matrix was designed to develop a luminance function by weighting the R, G, B signals in accordance with the CIE Photopic Spectral Luminance Efficiency Function, producing a video signal compatible with monochrome receivers. b) A signal that has major control of the image luminance. It is a linear combination of gamma-corrected primary color signals. c) The specific ratio of color primaries that provides a match to the white point in a specified color space.

d) The definition of luminance, television is identical for NTSC, PAL, and SECAM (CCIR Report 624-4), as follows: E'Y = (0.299) E'R + (0.587) E'G + (0.014) E'B. The weighting function is named luminance signal in all of the television standards. For convenience and bandwidth conservation, however, it is always formed from the gamma correction signals (i.e., R', G', B') and not from the initial linear signals, and thus it is not an exact representation of luminance, physics.