Performs a scale2x and scale3x operation on a HTML canvas

ScaleX.js

/*
JavaScript port of <http://scale2x.sourceforge.net/algorithm.html>
*/

var scaleX = (function (exports) {
  function getPixel32(data, x, y, w) {
    var id = (x + y * w) * 4;
    return (data[id] << 16) | (data[id + 1] << 8) | data[id + 2];
  }

  function setPixel32(data, x, y, w, value) {
    var id = (x + y * w) * 4;
    data[id] = (value >> 16) & 0xff;
    data[id + 1] = (value >> 8) & 0xff;
    data[id + 2] = value & 0xff;
    data[id + 3] = 0xff;
  }

  function scale2x(source, out) {
    var w = source.canvas.width;
    var h = source.canvas.height;
    var w2 = w * 2;
    var h2 = h * 2;
    var inputImageData = source.getImageData(0, 0, w, h);
    var inputData = inputImageData.data;

    console.assert(out.canvas.width === w2);
    console.assert(out.canvas.height === h2);

    var outputImageData = out.getImageData(0, 0, w2, h2);
    var outputData = outputImageData.data;

    var E, E0, E1, E2, E3, B, D, F, H, i, j, i2, j2;

    for (i = 0; i < w; i++) {
      for (j = 0; j < h; j++) {
        E = getPixel32(inputData, i, j, w);

        //edges handling
        if (i == 0 || j == 0 || i == w - 1 || j == h - 1) {
          E0 = E;
          E1 = E;
          E2 = E;
          E3 = E;
        } else {
          B = getPixel32(inputData, i, j - 1, w);
          D = getPixel32(inputData, i - 1, j, w);
          F = getPixel32(inputData, i + 1, j, w);
          H = getPixel32(inputData, i, j + 1, w);

          if (B != H && D != F) {
            E0 = D == B ? D : E;
            E1 = B == F ? F : E;
            E2 = D == H ? D : E;
            E3 = H == F ? F : E;
          } else {
            E0 = E;
            E1 = E;
            E2 = E;
            E3 = E;
          }
        }

        i2 = i * 2;
        j2 = j * 2;

        setPixel32(outputData, i2, j2, w2, E0);
        setPixel32(outputData, i2 + 1, j2, w2, E1);
        setPixel32(outputData, i2, j2 + 1, w2, E2);
        setPixel32(outputData, i2 + 1, j2 + 1, w2, E3);
      }
    }

    outputImageData.data = outputData;
    out.putImageData(outputImageData, 0, 0);

    return out;
  }

  function scale3x(source, out) {
    var w = source.canvas.width;
    var h = source.canvas.height;
    var w3 = w * 3;
    var h3 = h * 3;
    var inputImageData = source.getImageData(0, 0, w, h);
    var inputData = inputImageData.data;

    console.assert(out.canvas.width === w3, 'Output canvas width', out.canvas.width, w3);
    console.assert(out.canvas.height === h3, 'Output canvas height', out.canvas.height, h3);

    var outputImageData = out.getImageData(0, 0, w3, h3);
    var outputData = outputImageData.data;

    var E, E0, E1, E2, E3, E4, E5, E6, E7, E8, A, B, C, D, F, G, H, I, i, j, i3, j3;

    for (i = 0; i < w; i++) {
      for (j = 0; j < h; j++) {
        E = getPixel32(inputData, i, j, w);

        // edges handling
        if (i == 0 || j == 0 || i == w - 1 || j == h - 1) {
          E0 = E;
          E1 = E;
          E2 = E;
          E3 = E;
          E4 = E;
          E5 = E;
          E6 = E;
          E7 = E;
          E8 = E;
        } else {
          A = getPixel32(inputData, i - 1, j - 1, w);
          B = getPixel32(inputData, i, j - 1, w);
          C = getPixel32(inputData, i, j + 1, w);
          D = getPixel32(inputData, i - 1, j, w);
          F = getPixel32(inputData, i + 1, j, w);
          G = getPixel32(inputData, i - 1, j + 1, w);
          H = getPixel32(inputData, i, j + 1, w);
          I = getPixel32(inputData, i + 1, j + 1, w);

          if (B != H && D != F) {
            E0 = D == B ? D : E;
            E1 = (D == B && E != C) || (B == F && E != A) ? B : E;
            E2 = B == F ? F : E;
            E3 = (D == B && E != G) || (D == H && E != A) ? D : E;
            E4 = E;
            E5 = (B == F && E != I) || (H == F && E != C) ? F : E;
            E6 = D == H ? D : E;
            E7 = (D == H && E != I) || (H == F && E != G) ? H : E;
            E8 = H == F ? F : E;
          } else {
            E0 = E;
            E1 = E;
            E2 = E;
            E3 = E;
            E4 = E;
            E5 = E;
            E6 = E;
            E7 = E;
            E8 = E;
          }
        }

        i3 = i * 3;
        j3 = j * 3;

        setPixel32(outputData, i3, j3, w3, E0);
        setPixel32(outputData, i3 + 1, j3, w3, E1);
        setPixel32(outputData, i3 + 2, j3, w3, E2);
        setPixel32(outputData, i3, j3 + 1, w3, E3);
        setPixel32(outputData, i3 + 1, j3 + 1, w3, E4);
        setPixel32(outputData, i3 + 2, j3 + 1, w3, E5);
        setPixel32(outputData, i3, j3 + 2, w3, E6);
        setPixel32(outputData, i3 + 1, j3 + 2, w3, E7);
        setPixel32(outputData, i3 + 2, j3 + 2, w3, E8);
      }
    }

    outputImageData.data = outputData;

    out.putImageData(outputImageData, 0, 0);

    return out;
  }

  exports.scale2x = scale2x;
  exports.scale3x = scale3x;

  return exports;
})({});