Luminance

From Tech Artists Wiki

Luminance, plainly speaking, is the 'brightness' of a pixel. The values of the different channels (RGB) of a pixel are weighted differently- the most common weights being 0.2126, 0.7152, and 0.0722, for R, G, and B, respectively. This is because green light contributes the most to the intensity perceived by humans, and blue light the least.

The common functions page has two ways to compute luminosity:

• True Luminosity,
• and so-called Cheap Luminosity, which is less expensive to compute and uses the aforementioned weights.