问CSS对比度滤镜

EN

function contrastPixel(r,g,b,power) {
    r /= 255;  // normalize channels
    g /= 255;
    b /= 255;
    var rr = Math.pow(r,power);  // raise each to the power
    var gg = Math.pow(r,power);
    var bb = Math.pow(r,power);
    r = Math.floor((rr / (rr + Math.pow(1 - r, power)))*255);
    g = Math.floor((gg / (gg + Math.pow(1 - g, power)))*255);
    b = Math.floor((bb / (bb + Math.pow(1 - b, power)))*255);
    return {r,g,b};    
}

var dat = ctx.getPixelData(0,0,100,100);
var data = dat.data;
var i = 0;
while(i < data.length){
    var res = contrastPixel(data[i],data[i+1],data[i+2],power);
    data[i++] = res.r;
    data[i++] = res.g;
    data[i++] = res.b;
    i++;
}
ctx.putImageData(dat,0,0);

power = 1; // no change to the image
0 < power < 1; // reduces contrast
1 < power; // increases contrast

power = Math.pow(((Number(slider.value)* 0.0498) + 5)/5,Math.log2(10));