What is perceptual uniformity?
A system is perceptually uniform if a small perturbation to a component value is approximately equally perceptible across the range of that value. The volume control on your radio is designed to be perceptually uniform: rotating the knob ten degrees produces approximately the same perceptual increment in volume anywhere across the range of the control. If the control were physically linear, the logarithmic nature of human loudness perception would place all of the perceptual “action” of the control at the bottom of its range. The XYZ and RGB systems are far from exhibiting perceptual uniformity. Finding a transformation of XYZ into a reasonably perceptually-uniform space consumed a decade or more at the CIE and in the end no single system could be agreed. So the CIE standardized two systems, L*u*v* and L*a*b*, sometimes written CIELUV and CIELAB. (The u and v are unrelated to video U and V.) Both L*u*v* and L*a*b* improve the 80:1 or so perceptual nonuniformity of XYZ to about 6:1. Bot
