Bug in Sepia filter

[ddcovery]

When calculating the rgba.g the filter uses the modified rgba.r and not the original one. When calculating the rgba.b the filter uses the modified rgba.r, rgba.g instead the original ones.

This is a possible correction:

Filter.register "sepia", (adjust = 100) ->
  adjust /= 100
  @process "sepia", (rgba) ->
    r = rgba.r * (1 - 0.607 * adjust) + rgba.g * 0.769 * adjust + rgba.b * 0.189 * adjust
    g = rgba.r * 0.349 * adjust + rgba.g * (1 - 0.314 * adjust) + rgba.b * 0.168 * adjust
    b = rgba.r * 0.272 * adjust + rgba.g * 0.534 * adjust + rgba.b * (1- 0.869 * adjust)
    rgba.r = Math.min(255, r)
    rgba.g = Math.min(255, g)
    rgba.b = Math.min(255, b)

    rbga

[ddcovery]

One possible improvement, is to store de color matrix as 3 vectors (matrixR, matrixG, matrixB) and avoid to recalculate the same in each iteration.

Filter.register "sepia", (adjust = 100) ->
  adjust /= 100
  matrixR = [1 - 0.607 * adjust, 0.769 * adjust, 0.189 * adjust]
  matrixG = [0.349 * adjust, 1 - 0.314 * adjust, 0.168 * adjust]
  matrixB = [0.272 * adjust, 0.534 * adjust, 1 - 0.869 * adjust]

and then

    @process "sepia", (rgba) ->
      r = rgba.r * matrixR[0] + rgba.g * matrixR[1] + rgba.b * matrixR[2];
      g = rgba.r * matrixG[0] + rgba.g * matrixG[1] + rgba.b * matrixG[2];
      b = rgba.r * matrixB[0] + rgba.g * matrixB[1] + rgba.b * matrixB[2];
      ....

and then

[av01d]

Which then results in the following vanilla Javascript:

  Filter.register("sepia", function(adjust) {
    if (adjust == null) {
      adjust = 100;
    }
    adjust /= 100;
    var matrixR = [1 - 0.607 * adjust, 0.769 * adjust, 0.189 * adjust],
        matrixG = [0.349 * adjust, 1 - 0.314 * adjust, 0.168 * adjust],
        matrixB = [0.272 * adjust, 0.534 * adjust, 1 - 0.869 * adjust];
    return this.process("sepia", function(rgba) {
      var r = rgba.r * matrixR[0] + rgba.g * matrixR[1] + rgba.b * matrixR[2],
          g = rgba.r * matrixG[0] + rgba.g * matrixG[1] + rgba.b * matrixG[2],
          b = rgba.r * matrixB[0] + rgba.g * matrixB[1] + rgba.b * matrixB[2];
      rgba.r = Math.min(255, r);
      rgba.g = Math.min(255, g);
      rgba.b = Math.min(255, b);
      return rgba;
    });
  });