window.onload = function () {

            var img = new Image();

            img.src = '1.gif';

            var ctx = document.querySelector('#aa').getContext('2d');

            img.onload = function () {

                ctx.drawImage(img, 0, 0, img.width, img.height, 0, 0, 400, 400);

                var a = ctx.getImageData(0, 0, 100, 100), data = a.data;

                for (var i = 0, len = data.length; i < len; i += 4) {

                    data[i] = 0; //r

                    data[i + 1] = 0; //g

                    data[i + 2] = 0; //b

                    data[i+3]=255; //alpha 

                }

                ctx.putImageData(a, 0, 0);

            }

        }