輝度による文字色の除外を追加

fladdict.js

function Fladdict(img) {
  this.image = img;
  this.canvas;
  this.context;
  this.backgroundColor;
  this.textColor = [];
  this.edgeColor;
  this.colorHistogram;
}

Fladdict.prototype.process = function() {
  var image = this.image;
  var canvas;
  var context;

  if (image instanceof HTMLImageElement) {
    canvas = this.canvas = document.createElement('canvas');
    context = this.context = canvas.getContext('2d');
    canvas.width = image.width;
    canvas.height = image.height;
    context.drawImage(image, 0, 0);
  } else if (image instanceof HTMLCanvasElement) {
    canvas = this.canvas = image;
    this.context = canvas.getContext('2d');
  }

  this.processColorHistogram();
  this.processBackgroundColor();
  this.processTextColor();
  this.processTextColor();
};

Fladdict.prototype.processColorHistogram = function() {
  var canvas = this.canvas;
  var context = this.context;
  var width = canvas.width;
  var height = canvas.height;
  var imageData = context.getImageData(0, 0, width, height);
  var pixelArray = imageData.data;
  var hist = this.colorHistogram = new Uint32Array(512);
  var edge = this.edgeColor = new Uint32Array(512);
  var x;
  var y;
  var pos;
  var color;

  for (y = 0; y < height; ++y) {
    for (x = 0; x < width; ++x) {
      pos = (y * width + x) * 4;

      // color reduction
      color =
        Fladdict.rgb2int(pixelArray[pos], pixelArray[pos+1], pixelArray[pos+2]);
      hist[color]++;

      // edge
      if (x === 0 || x === width-1 || y === 0 || y === height-1) {
        edge[color]++;
      }
    }
  }
};

Fladdict.prototype.processBackgroundColor = function() {
  var hist = this.colorHistogram;
  var edge = this.edgeColor;
  var color = 0;
  var i, il;

  for (i = 0, il = edge.length; i < il; ++i) {
    if (edge[i] > 0 && hist[i] > hist[color]) {
      color = i;
    }
  }

  this.backgroundColor = Fladdict.int2rgb(color);
};

Fladdict.prototype.processTextColor = function() {
  var max = -1;
  var maxColor;
  var hist = this.colorHistogram;
  var bgrgb = this.backgroundColor;
  var bgint = Fladdict.rgb2int(bgrgb);
  var bghsv = Fladdict.rgb2hsv(bgrgb);
  var bgy = Fladdict.rgb2y(bgrgb);
  var text = this.textColor;

  Array.prototype.forEach.call(hist, function(v, color) {
    var rgb = Fladdict.int2rgb(color);
    var hsv;
    var sub;
    var y;

    // background color
    if (color === bgint) {
      return;
    }

    // text color
    for (i = 0, il = text.length; i < il; ++i) {
      if (color === Fladdict.rgb2int.apply(this, text[i])) {
        return;
      }
    }

    // color check
    hsv = Fladdict.rgb2hsv(rgb);
    sub = hsv[0] - bghsv[0];
    y = Fladdict.rgb2y(rgb);
    if (
      Math.abs(sub > 180 ? sub - 360 : sub) < 120 ||
      Math.abs(hsv[2] - bghsv[2]) < 96 ||
      Math.abs(y - bgy) < 96
    ) {
      return;
    }

    if (max < v) {
      max = v;
      maxColor = color;
    }
  });

  text.push(Fladdict.int2rgb(maxColor));
};

Fladdict.rgb2int = function(red, green, blue) {
  return (
    ((red   >> 5) << 6) |
    ((green >> 5) << 3) |
    ((blue  >> 5) << 0)
  );
};

Fladdict.int2rgb = function(color) {
  return [
    ((color >> 6 & 0x7) << 5) + 16,
    ((color >> 3 & 0x7) << 5) + 16,
    ((color >> 0 & 0x7) << 5) + 16
  ];
};

Fladdict.rgb2hsv = function(rgb) {
  var max = Math.max.apply(null, rgb);
  var min = Math.min.apply(null, rgb);
  var hue =
    max === rgb[0] ? 60 * (rgb[1] - rgb[2]) / (max - min)       :
    max === rgb[1] ? 60 * (rgb[2] - rgb[0]) / (max - min) + 120 :
  /*max === rgb[2]*/ 60 * (rgb[0] - rgb[1]) / (max - min) + 240;
  var saturation = (max - min) / max;

  if (max === min) { hue = 0; }
  if (max === 0) { saturation = 0; }
  if (hue < 0) { hue += 360; }

  return [hue, saturation, max];
};

Fladdict.rgb2y = function(rgb) {
  return 0.298912 * rgb[0] + 0.586611 * rgb[1] + 0.114478 * rgb[2] + 0.5 | 0;
};