User:Joger/Color Management
This document contains personal draft notes on color management topics, and can not be considered a reference on the topic.
Definitions
Luminance, denoted Y, unit cd·m-2 (nits) is a linear light quantity, where physical intensity is weighted by the sensitivity of human vision. Luminance is an integral over a spectral power distribution but because of the way the eye works, it can also be calculated as a weighted sum of linear-light red, green, and blue tristimulus components[1], and takes human sensitivity to different wavelengths into account. Luminance is typically not used in video processing, because we rarely intend to reproduce the absolute luminance of the actual scene[1].
Relative luminance, is a unitless quantity, and is proportional to the scene luminance up to the maximum luminance of the screen. Relative luminance is calculated by normalizing the scene luminance to 1 or 100 units, relative to a reference white[1] which is assumed to appear white to the observer in the ambient environment.
Luma, denoted Y' , is calculated as a weighted sum of gamma corrected R', G', and B' components[1].