Canvas Pixel Manipulation

JavaScript performance comparison

Revision 87 of this test case created by mattdesl

Info

Tests two different methods of manipulating pixels using the canvas.

NOTE: Now takes endianness into account.

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;
    }
   
   
    function rgba_LE(pixels, index, r, g, b, a) {
        pixels[index] = (a   << 24) |  // alpha
                        (b << 16) |    // blue
                        (g <<  8) |    // green
                         r;            // red
    }
   
    function rgba_BE(pixels, index, r, g, b, a) {
        pixels[index] = (r << 24) |    // red
                        (g << 16) |    // green
                        (b <<  8) |    // blue
                         a;            // alpha
    }
   
    function rgba_8bit(pixels, index, r, g, b, a) {
        pixels[index] = r;
        pixels[++index] = g;
        pixels[++index] = b;
        pixels[++index] = a;
    }
   
   
    var rgba_32 = isLittleEndian ? rgba_LE : rgba_BE;
   
   
};

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

        var value = x * y & 0xff;

        rgba_8bit(data, index, value, value, value, 255);
    }
}
pending…
32-bit Pixel Manipulation
for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
        var value = x * y & 0xff;

        rgba_32(data32, y * canvasWidth + x, value, value, value, 255);
    }
}
pending…

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