canvas_image_edge_detection.js

function doEdgeDetectionAlgorithm(input, baseColor, grey) {
    var output = context.createImageData(canvas.width, canvas.height);
    var w = input.width, h = input.height;
    var inputData = input.data;
    var outputData = output.data;
    var bytesPerRow = w * 4;
    var pixel = bytesPerRow + 4; // Start at (1,1)
    var hm1 = h - 1;
    var wm1 = w - 1;
    var d = new Date;
    for (var y = 1; y < hm1; ++y) {
        // Prepare initial cached values for current row
        var centerRow = pixel - 4;
        var priorRow = centerRow - bytesPerRow;
        var nextRow = centerRow + bytesPerRow;
        var r1 = - inputData[priorRow]   - inputData[centerRow]   - inputData[nextRow];
        var g1 = - inputData[++priorRow] - inputData[++centerRow] - inputData[++nextRow];
        var b1 = - inputData[++priorRow] - inputData[++centerRow] - inputData[++nextRow];
        var rp = inputData[priorRow += 2];
        var rc = inputData[centerRow += 2];
        var rn = inputData[nextRow += 2];
        var r2 = - rp - rc - rn;
        var gp = inputData[++priorRow];
        var gc = inputData[++centerRow];
        var gn = inputData[++nextRow];
        var g2 = - gp - gc - gn;
        var bp = inputData[++priorRow];
        var bc = inputData[++centerRow];
        var bn = inputData[++nextRow];
        var b2 = - bp - bc - bn;
        
        // Main convolution loop
        for (var x = 1; x < wm1; ++x) {
            centerRow = pixel + 4;
            priorRow = centerRow - bytesPerRow;
            nextRow = centerRow + bytesPerRow;
            var r = baseColor + r1 - rp - (rc * -8) - rn;
            var g = baseColor + g1 - gp - (gc * -8) - gn;
            var b = baseColor + b1 - bp - (bc * -8) - bn;
            r1 = r2;
            g1 = g2;
            b1 = b2;
            rp = inputData[priorRow];
            rc = inputData[centerRow];
            rn = inputData[nextRow];
            r2 = - rp - rc - rn;
            gp = inputData[++priorRow];
            gc = inputData[++centerRow];
            gn = inputData[++nextRow];
            g2 = - gp - gc - gn;
            bp = inputData[++priorRow];
            bc = inputData[++centerRow];
            bn = inputData[++nextRow];
            b2 = - bp - bc - bn;
            if( !grey ) {
                outputData[pixel] = r + r2;
                outputData[++pixel] = g + g2;
                outputData[++pixel] = b + b2;
            } else {
                factor = .3* (r+r2) + .59*(g+g2) +.11*(b+b2);
                outputData[pixel] = factor;
                outputData[++pixel] = factor;
                outputData[++pixel] = factor;
            }
            outputData[++pixel] = 255; // alpha
            ++pixel;
        }
        pixel += 8;
    }
    //alert((new Date - d) / 1000);
    return output;
}