"The Importance of Being Linear" is an excellent article, but there is a caveat. What do we mean by linear? A linear change in RGB equals a linear change in ph

"The Importance of Being Linear" is an excellent article, but there is a caveat. What do we mean by linear? A linear change in RGB equals a linear change in photons output? Let's call this physically-linear. Or do we mean that if we sit 100 people down and show them rgb(32, 64, 16) and then rgb(64, 128, 32) that they agree that the second is "twice as bright"? Let's call this perceptually-linear. Physical and perceptual linearity are not the same and have different use cases. Physical linearity is important when you are simulating lighting: shadows, shading, etc. etc. Perceptual linearity is probably more important when it comes to scientific visualization, because we are trying to use colour as a form of transmission of information from the computer into our heads, so it makes sense to "spread" out the colour as much as possible (note: I do not have a background in visualization, just experience in CG. I welcome input from those who know the field better.) Physical-linearity is as "easy" as calibrating to your monitor (gamma, etc.) Perceptual-linearity is... harder. You can start by investigating CIE-LAB colour spaces etc., but the story most definitely does not end there (for example, check out "Interaction of Color" by Josef Albers.)