灰度图

//灰度图
        function greyEffect(imageData) {
            pixelData = imageData.data;
            for (var i = 0; i < canvas.width * canvas.height; i++) {
                var r = pixelData[i * 4 + 0],
                    g = pixelData[i * 4 + 1],
                    b = pixelData[i * 4 + 2];
                var grey = 0.3 * r + 0.59 * g + 0.11 * b;
                pixelData[i * 4 + 0] = grey;
                pixelData[i * 4 + 1] = grey;
                pixelData[i * 4 + 2] = grey;
            }
            imageData.data = pixelData;
            return imageData;
        }

//去色滤镜
        function removeColor(imageData) {
            pixelData = imageData.data;
            for (var i = 0; i < canvas.width * canvas.height; i++) {
                var r = pixelData[i * 4 + 0],
                    g = pixelData[i * 4 + 1],
                    b = pixelData[i * 4 + 2];
                var c = Math.floor((Math.min(r, g, b) + Math.max(r, g, b)) / 2);
                pixelData[i * 4 + 0] = c;
                pixelData[i * 4 + 1] = c;
                pixelData[i * 4 + 2] = c;
            }
            imageData.data = pixelData;
            return imageData;
        }