Originally Posted by wchris
That is only true for 100% saturated targets . Everything 'below' changes when gamma does, not only the luminance. That's because the triplet for i.e. 25% saturated patch is not constant. It is based on display gamma.
Luminance controls gamma. Saturation does not. You can have 2.25 gamma with 100% saturated targets or 50% saturated, or 25% saturated. The TV may or may not track that correctly. Gamma is difficult to conceive-of in RGB mode, in uvL (hue, saturation, Luminance) space, Gamma is much easier to visualize and conceptualize. Things have to happen in RGB space in ways they do not happen in uvL space.
When you work with gamma on a step by step basis, and you have a graph that shows red, green, and blue bars... you are looking at Red luminance, green luminance, and blue luminance. You want them all equal to achieve any specific grayscale step. When you're at 50% white, you still want red, green, and blue luminance to "match" each other so the step is as close to neutral gray as you can get. This is difficult to conceptualize in RGB space, much easier when you think in terms of uvL space.