code: function ColorStepFilter()
  {
      core.AbstractFilter.call(this,
          // vertex shader
          null,
          // fragment shader
          fs.readFileSync(__dirname + '/colorStep.frag', 'utf8'),
          // custom uniforms
          {
              step: { type: '1f', value: 5 }
          }
      );
  }
docs: This lowers the color depth of your image by the given amount, producing an image with a smaller palette.
  
  @class
  @extends AbstractFilter
  @memberof PIXI.filters