Canvas Pixel Manipulation

JavaScript performance comparison

Revision 138 of this test case created by

Preparation code

<canvas id="canvas" height="256" width="256"></canvas>
      
<script>
Benchmark.prototype.setup = function() {
  var canvas = document.getElementById('canvas');
  var canvasWidth = canvas.width;
  var canvasHeight = canvas.height;
  var ctx = canvas.getContext('2d');
  var imageData = ctx.getImageData(0, 0, canvasWidth, canvasHeight);
  
  var data = imageData.data;
  
  
  var buf = new ArrayBuffer(imageData.data.length);
  var buf8 = new Uint8ClampedArray(buf);
  var data32 = new Uint32Array(buf);
  
  var pixels = new Int32Array(imageData.data.buffer);

};

Benchmark.prototype.teardown = function() {
  ctx.putImageData(imageData, 0, 0);

};
</script>

Preparation code output

<canvas id="canvas" height="256" width="256"></canvas>

Test runner

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Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
8-bit read alpha
var c = 0;
var len = data.length / 4;

for (var i = 0; i < len; i++) {

  var alpha = data[i + 3];
  if (alpha !== 0) {
    c++;
  }
}
pending…
32-bit read alpha
var c = 0;

var c = 0;
var len = pixels.length;

for (var i = 0; i < len; i++) {

  var alpha = (pixels[i] >> 24) & 0xFF;
  if (alpha !== 0) {
    c++;
  }
}
pending…
32-bit read alpha flat
var c = 0;
var len = pixels.length;

for (var i = 0; i < len; i++) {
  var alpha = pixels[i] & 0xFF000000;
  if (alpha !== 0) {
    c++;
  }
}
pending…

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