function converttoGS(img) {
    img.color = img.src;

    img.grayscale = createGSCanvas(img);
    img.onmouseover = function () {
        this.src = http://www.mamicode.com/this.color;
    }
    img.onmouseout = function () {
        this.src = http://www.mamicode.com/this.grayscale;
        alert(this.src)
    }
}
function createGSCanvas(img) {
    var canvas = document.createElement(‘canvas‘);
    canvas.width = img.width;
    canvas.height = img.height;

    var ctx = canvas.getContext(‘2d‘);
    ctx.drawImage(img,0,0);

    var c = ctx.getImageData(0,0,img.width,img.height);
    for(var i = 0; i <c.height;i++){
        for(var j = 0; j<c.width; j++){
            var x = (i*4)*c.width+(j*4);
            var r = c.data[x];
            var g = c.data[x+1];
            var b = c.data[x+2];
            c.data[x] = c.data[x+1] = c.data[x+2]=(r+g+b)/3;
        }
    }

    ctx.putImageData(c,0 ,0,0,0,c.width,c.height)
    return canvas.toDataURL();
}

img 黑白版与彩色版切换