Function paethPredictor

dependency/densecrf/examples/lodepng.cpp:3829–3838

Paeth predicter, used by PNG filter type 4 The parameters are of type short, but should come from unsigned chars, the shorts are only needed to make the paeth calculation correct. */

 are only needed to make the paeth calculation correct.
 */
static unsigned char paethPredictor(short a, short b, short c)
{
    short pa = abs(b - c);
    short pb = abs(a - c);
    short pc = abs(a + b - c - c);
    
    if(pc < pa && pc < pb) return (unsigned char)c;
    else if(pb < pa) return (unsigned char)b;
    else return (unsigned char)a;
}

/*shared values used by multiple Adam7 related functions*/