proc.js

function proc(readers, channel, cmp_mode, quality_metric, quality_result) {
  channel = channel || 0;
  cmp_mode = readers.length > 1 ? (cmp_mode || 0) : 0;
  quality_metric = readers.length > 1 ? (quality_metric || 0) : 0;
  var width = readers[0].width;
  var height = readers[0].height;
  if (readers.length > 1) {
    width = Math.min(width, readers[1].width);
    height = Math.min(height, readers[1].height);
  }

  var mse_y = 0;

  var rgb = new ImageData(width, height);
  for (var py = 0; py < height; ++py) {
    for (var px = 0; px < width; ++px) {
      var p1 = readers[0].yuv(py, px);
      var p2 = readers.length > 1 ? readers[1].yuv(py, px) : p1;

      if (channel != 0) {
        if (channel == 2) {
          p1[0] = p1[1];
          p2[0] = p2[1];
        } else if (channel == 3) {
          p1[0] = p1[2];
          p2[0] = p2[2];
        }

        p1[1] = p1[2] = 128;
        p2[1] = p2[2] = 128;
      }

      if (cmp_mode > 0 || quality_metric > 0) {
        var dy = Math.abs(p1[0] - p2[0]);
        var du = Math.abs(p1[1] - p2[1]);
        var dv = Math.abs(p1[2] - p2[2]);

        if (cmp_mode == 1) {
          p1[0] = dy;
          p1[1] = du + 128;
          p1[2] = dv + 128;
        } else if (cmp_mode == 2) {
          var d = dy | du | dv;
          p1[0] = 255 * !!d;
          p1[1] = 128;
          p1[2] = 128;
        }

        if (quality_metric == 1) {
          mse_y += dy * dy;
        }
      }

      var y = p1[0] * 128;
      var u = p1[1] - 128;
      var v = p1[2] - 128;

      var b = (y + 164 * v) >> 7;
      var g = (y - 28 * u - 49 * v) >> 7;
      var r = (y + 272 * u) >> 7;
      var irgb = 4 * (py * width + px);
      rgb.data[irgb++] = b > 255 ? 255 : (b < 0 ? 0 : b);
      rgb.data[irgb++] = g > 255 ? 255 : (g < 0 ? 0 : g);
      rgb.data[irgb++] = r > 255 ? 255 : (r < 0 ? 0 : r);
      rgb.data[irgb++] = 255;
    }
  }

  if (quality_metric == 1) {
    quality_result['psnr_y'] = 20 * log10(255)
        - 10 * log10(1.0 * Math.max(mse_y,1) / (width * height));
  }

  return rgb;
}

function log10(val) {
  return Math.log(val) / Math.LN10;
}