However, over small ranges, hue can be ordered. For example, unique yellow contains no trace of either red or green. In a sense, it is the most intense sensation of yellowness possible. For example, there is a common color vision exam, the Farnsworth-Munsell Test, which requires observers to properly order colored chips in this way. Second, saturation, the amount of white mixed with a spectral, i. e., the purest, hue, is also an ordered variable.
Viewers can readily order lights by increasing amounts of saturation.
If this idea is correct, then it should be easy, using existing psychophysical data, to promote brightness to a quantitative level of organization by rescaling the intensity axis. The solution is to scale the X axis in Figure 8a so that the curved line becomes straight, i. e., make the steps at the low end of the scale larger. The nonlinear gamma built into most CRT monitors rescales brightness-grey level function to compensate for the visual brightness nonlinearity. However, degree of compensation is often overstated for two reasons. First, the visual system s brightness exponent varies with conditions and can be as low as 0.33.