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Improve performance of grayscale calculation steps #2

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46bd704
Reduce loops and pixel position math
developher-net Oct 24, 2012
fe70edf
Grayscale calculation using standard Luma formula
developher-net Oct 24, 2012
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19 changes: 9 additions & 10 deletions js/grayscale.js
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Original file line number Diff line number Diff line change
Expand Up @@ -38,16 +38,15 @@ return this.each(function(){

var imgPixels = ctx.getImageData(0, 0, canvas.width, canvas.height);

for(var y = 0; y < imgPixels.height; y++){
for(var x = 0; x < imgPixels.width; x++){
var i = (y * 4) * imgPixels.width + x * 4;
var avg = (imgPixels.data[i + 0] + imgPixels.data[i + 1] + imgPixels.data[i + 2]) / 3;

imgPixels.data[i + 0] = avg;
imgPixels.data[i + 1] = avg;
imgPixels.data[i + 2] = avg;
}
}
for(var i = 0, n = imgPixels.data.length; i < n; i += 4) {
//Calculate monochrome value using Classic Luma formula used by most image processing software
var avg = imgPixels.data[i + 0] * 0.2126 + imgPixels.data[i + 1] * 0.7152 + imgPixels.data[i + 2] * 0.0722;

imgPixels.data[i + 0] = avg; //red channel
imgPixels.data[i + 1] = avg; //blue channel
imgPixels.data[i + 2] = avg; //green channel
// i + 4 would be the alpha channel
}

ctx.putImageData(imgPixels, 0, 0, 0, 0, imgPixels.width, imgPixels.height);
$this.attr('src',canvas.toDataURL());
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