用canvas实现图片滤镜效果详解之灰度效果

for ( var x = 0; x < canvasData.width; x++) {

var idx = (x + y * canvasData.width) * 4;

var g = canvasData.data[idx + 1];

var gray = .299 * r + .587 * g + .114 * b;

// assign gray scale value

canvasData.data[idx + 1] = gray; // Green channel

canvasData.data[idx + 3] = 255; // Alpha channel

if(x < 8 || y < 8 || x > (canvasData.width - 8) || y > (canvasData.height - 8))

canvasData.data[idx + 0] = 0;

canvasData.data[idx + 2] = 0;

}