Canvas Pixel Manipulation

JavaScript performance comparison

Revision 10 of this test case created by PlayMyCode

Info

Tests two different methods of manipulating pixels using the canvas.

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

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Testing in unknown unknown
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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