Live-Dimension : I think that's a safe bet. I don't think I've ever used an indexed-mode paint program that didn't have that feature.
Yes, although most of them do it quite wrongly; even most dedicated palette editors do it wrongly. For example, a correct 3-step graduation between intensity 0 and intensity 255 is NOT [64, 128, 192] but rather [137, 188, 225], because a proper interpolation is linear in the visual relationship of the intensities, and standard RGB is nonlinear in that respect.
Interpolating HSV/HSL also only makes proper sense when you derive the HSV/HSL values from linear RGB values.
So, it's worth mentioning as a suggestion:
correct interpolation.
The formulas for converting between linear and standard sRGB, after they are converted to floats in the range [0..1]
when intensity < 0.0031308
result = 12.92 * intensity
otherwise
result = (1.055 * (intensity ^ (1.0 / 2.4))) - 0.055
when intensity <= 0.04045
result = intensity / 12.92
otherwise
result = ((intensity + 0.055) / 1.055) ^ 2.4
Using linear rgb can also improve other things, like the antialiasing filter and well... anything that combines colors mathematically to create a new color, really.
Using the above formulas, you can see that standard rgb values 64, 128, 192 are not on a straight line through the middle of the range 0..255, but on a curve along the bottom of the range 0..255; 64, 128, 192 convert to linear RGB intensities 13, 55, 133.
an example of the difference that correct interpolation can make:
top row is incorrectly calculated (interpolating through standard RGB), next row is correctly calculated (interpolating through linear RGB).
the rest of the rows just illustrate interpolation through other colorspaces.
