Optimal coloring algorithms and palettes

Question

Falling around google and found nothing like what I need. so what is it me ok two things:

• Firstly, I am looking for an Algorithm / pseudo-code / white wallpaper to determine the best color for an r, g, b tuple and an array of 256 RGB tuples.

• Secondly, I am looking for an algorithm / pseudo-code / documents to repaint the 8-bit image of the palette (using the RGB palette above), either taking into account Hue / Saturation or r, g, b channel modification. It will also be nice if you could add a correction for gamma and artifact pixels in the coloring as well.

does anyone have hints / pointers / hints as to where I can find such a thing (I know that they must exist, otherwise some photoshop functions will not work)

UPDATE: here is the basic RGB Euclidean distance for finding a palette index:

uint_8 __stdcall GFXUTIL_GetNearestPaletteIndex(const uint_8* pPalette, size_t nSize, uint_8 nRed, uint_8 nGreen, uint_8 nBlue)
{
    if(pPalette == NULL)
        return 0;

    int nDistance = -1;
    size_t nIndex = 0, nFoundIndex = 0;
    while(nIndex < nSize)
    {
        int nDistRed = pPalette[0] - nRed;
        int nDistGreen = pPalette[1] - nGreen;
        int nDistBlue = pPalette[2] - nBlue;
        int nCurrentDistance = (nDistRed * nDistRed) + (nDistGreen * nDistGreen) + (nDistBlue * nDistBlue);
        if(nCurrentDistance < nDistance)
        {
            nFoundIndex = nIndex;
            nDistance = nCurrentDistance;
        }

        nIndex++;
        pPalette += sizeof(uint_32);
    }

    return nFoundIndex;
} 

Answer 1

See http://en.wikipedia.org/wiki/Color_difference to calculate the distance between colors, taking into account the sensitivity of the human eye.

Answer 2

If you want it faster than linear, then look at VP-tree or KD-tree.

If you want it to be perceptually accurate, search the Lab Color Space .