Canvas Pixel Manipulation

JavaScript performance comparison

Revision 49 of this test case created by Dan H

Info

Tests two different methods of manipulating pixels using the canvas.

NOTE: Now takes endianness into account.

Remove needless index recalculation every iteration

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);
   
    // Determine whether Uint32 is little- or big-endian.
    data32[1] = 0x0a0b0c0d;
   
    var isLittleEndian = true;
    if (buf[4] === 0x0a && buf[5] === 0x0b && buf[6] === 0x0c && buf[7] === 0x0d) {
      isLittleEndian = false;
    }
};

Benchmark.prototype.teardown = function() {
    ctx.putImageData(imageData, 0, 0);
};
</script>

Preparation code output

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Testing in unknown unknown
Test Ops/sec
8-bit Pixel Manipulation
var index = 0;
for (var y = 0; y < canvasHeight; ++y) {
  for (var x = 0; x < canvasWidth; ++x) {

    var value = x * y & 0xff;

    data[index++] = value; // red
    data[index++] = value; // green
    data[index++] = value; // blue
    data[index++] = 255; // alpha
  }
}
pending…
32-bit Pixel Manipulation
var index = 0;
if (isLittleEndian) {
  var alpha = 255 << 24;
  for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
      var value = x * y & 0xff;

      data32[index++] = alpha | // alpha
      (value << 16) | // blue
      (value << 8) | // green
      value; // red
    }
  }
} else {
  for (y = 0; y < canvasHeight; ++y) {
    for (x = 0; x < canvasWidth; ++x) {
      value = x * y & 0xff;

      data32[index++] = (value << 24) | // red
      (value << 16) | // green
      (value << 8) | // blue
      255; // alpha
    }
  }
}

imageData.data.set(buf8);
pending…

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