Canvas Pixel Manipulation

JavaScript performance comparison

Revision 10 of this test case created by PlayMyCode

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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Java applet disabled.

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

for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
        var i = (y * canvasWidth + x)*4;

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

for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
        var i = y * canvasWidth + x;

        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…
32-bit Pixel Manipulation direct alpha
pending…

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