canvas_pixels_from_jpg.html
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<html>
<head>
<title>Canvas test</title>
</head>
<body>
<img src="../img/mandelbrot_wp.jpg" />
<canvas id="canvas-cible" width="322" height="242" ></canvas>
<script type="text/javascript">
window.onload = function(){
var testCanvas = document.createElement('canvas');
if (testCanvas.getContext === undefined) {
document.writeln('Browser too old!.');
} else {
var canvas = document.getElementById("canvas-cible");
var context = canvas.getContext("2d");
var imageObj = new Image();
imageObj.onload = function(){
context.drawImage(imageObj, 0, 0);
var imgData = context.getImageData(0, 0, canvas.width, canvas.height);
var pixels = imgData.data;
for (var i = 0; i < pixels.length; i += 4) {
var grayscale = pixels[i] * .3 + pixels[i+1] * .59 + pixels[i+2] * .11;
pixels[i ] = grayscale; // red
pixels[i+1] = grayscale; // green
pixels[i+2] = grayscale; // blue
// pixels[i+3] est le canal alpha
}
context.putImageData(imgData, 0, 0);
};
imageObj.src = "../img/mandelbrot_wp.jpg";
}
};
</script>
</body>
</html>