How do I determine if a color is closer to white or black?

Question

I am dealing with images and would like to determine if a set of pixels are closer to white or black.

So given a set of colors/pixles, how does one det

Answer 1

There are two potential meanings of white and black:

• Colour spectrum of visible light
• Human skin tones as determined by race, amount of tan etc.

The former is easy: convert to greyscale range 0-255. 127 or less is closer to black (0), 128 or above is closer to white (255).

I use the following function to convert to greyscale using luminance values (assuming an int ARGB format for input colour):

public static int getLuminance(int argb) {
    int lum= (   77  * ((argb>>16)&255) 
               + 150 * ((argb>>8)&255) 
               + 29  * ((argb)&255))>>8;
    return lum;
}

The latter definition (human skin tones) is impossible to do with a simple algorithm as it depends on light condition, camera settings, exposure etc. An RGB vlaue of (190,115,60) is probably approximately the midpoint in typical conditions