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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Grayscale</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d');
//draw some stripes: red, green, and blue
for (var i = 0; i < canvas.width; i += 10) {
for (var j = 0; j < canvas.height; j += 10) {
context.fillStyle = (i % 20 === 0) ? "#f00" : ((i % 30 === 0) ? "#0f0" : "#00f");
context.fillRect(i, j, 10, 10);
}
}
var imagedata = context.getImageData(0, 0, canvas.width, canvas.height),
pixels = imagedata.data;
//pixel iteration
for (var offset = 0, len = pixels.length; offset < len; offset += 4) {
var r = pixels[offset],
g = pixels[offset + 1],
b = pixels[offset + 2],
y = (0.2126 * r) + (0.7152 * g) + (0.0722 * b); //relative luminance, humans perceive green more
pixels[offset] = pixels[offset + 1] = pixels[offset + 2] = y;
}
context.putImageData(imagedata, 0, 0);
};
</script>
</body>
</html>