for ( var x = 0; x < canvasData.width; x++) {
for ( var y = 0; y < canvasData.height; y++) {
var idx = (x + y * canvasData.width) * 4;
var r = canvasData.data[idx + 0];
var g = canvasData.data[idx + 1];
var b = canvasData.data[idx + 2];
var gray = .299 * r + .587 * g + .114 * b;
canvasData.data[idx + 0] = gray;
canvasData.data[idx + 1] = gray;
canvasData.data[idx + 2] = gray;
canvasData.data[idx + 3] = 255;
if(x < 8 || y < 8 || x > (canvasData.width - 8) || y > (canvasData.height - 8))
{
canvasData.data[idx + 0] = 0;
canvasData.data[idx + 1] = 0;
canvasData.data[idx + 2] = 0;
}
}
}