Gamma-Corrected color distance

/* Return gamma-corrected value of a color component byte*/
float GCRGB(byte component) {
   static float GCRGBTable[256] = {0.0f};
   static int loaded = 0;

   if(!loaded) {
      int i;
      for(i = 0; i < 256; ++i) {
         GCRGBTable[i] = pow(i/255.0f, 2.2f);
      }
      loaded = 1;
   }

   return GCRGBTable[component];
}

float difference(Color c1, Color c2) {
   float r, g, b;
   r = GCRGB(c1.r) - GCRGB(c2.r);
   g = GCRGB(c1.g) - GCRGB(c2.g);
   b = GCRGB(c1.b) - GCRGB(c2.b);



   return r*r + g*g + b*b;
}