Logarithmic contrast

log_setContrast.js

function setContrast(rgb, perc)
{
    ret = {}
    Object.keys(rgb).map(function(v) {
        col = rgb[v];
        if (perc <= 0) {
            col += (col - 128) * perc / 100; // ---> 128
        } else {
           if (col < 128) {
               //bad start
               qe = col / Math.log(col);
               col = Math.log(101 - perc) * qe; // ---> 0
           } else {
               //bad start
               diff = 255 - col;
               qe = diff/Math.log(diff+1);
               col = 255 - Math.log(101 - perc) * qe; // ---> 255
           }
        }
        
        ret[v] = parseInt(col);
    });
    return ret;
}