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