konva/src/filters/Levels.js

(function () {

  /**
   * Levels Filter. Adjusts the channels so that there are no more
   *  than n different values for that channel. This is also applied
   *  to the alpha channel.
   *  Performs w*h pixel reads and w*h pixel writes.
   * @function
   * @author ippo615
   * @memberof Kinetic.Filters
   * @param {ImageData} src, the source image data (what will be transformed)
   * @param {ImageData} dst, the destination image data (where it will be saved)
   * @param {Object} opt
   * @param {Number} [opt.quantizationLevels], the number of values allowed for each
   *  channel. Between 2 and 255. Default is 2. 
   */

  var Levels = function (src, dst, opt) {
    var nLevels = Math.round(opt.quantizationLevels || 2);
    var srcPixels = src.data,
      dstPixels = dst.data,
      nPixels = srcPixels.length,
      scale = (255 / nLevels),
      i;
    for (i = 0; i < nPixels; i += 1) {
      dstPixels[i] = Math.floor(srcPixels[i] / scale) * scale;
    }
  };

  Kinetic.Filters.Levels = function(src,dst,opt){
    if( this === Kinetic.Filters ){
      Levels(src, dst||src, opt );
    }else{
      Levels.call(this, src, dst||src, {
        quantizationLevels: this.getQuantizationLevels()
      });
    }
  };

  Kinetic.Factory.addFilterGetterSetter(Kinetic.Node, 'quantizationLevels', 4);

    /**
    * get quantization levels.  Returns the number of unique levels for each color
    * channel. 2 is the minimum, 255 is the maximum. For Kinetic.Filters.Levels
    * @name getQuantizationLevels
    * @method
    * @memberof Kinetic.Image.prototype
    */

    /**
    * get quantization levels.  Sets the number of unique levels for each color
    * channel. 2 is the minimum, 255 is the maximum. For Kinetic.Filters.Levels
    * @name setQuantizationLevels
    * @method
    * @memberof Kinetic.Image.prototype
    */
})();