code: function (x, y, width, height) {
  
  		var image;
  
  		width = Math.min(width, this.getWidth() - x);
  		height = Math.min(height, this.getHeight() - y);
  
  		if ((width < 0) || (height < 0)) {
  			throw new Error('Width and height cannot be negative.');
  		}
  
  		image = new PNG({
  			width: width, height: height
  		});
  
  		this._image.bitblt(image, x, y, width, height, 0, 0);
  		this._image = image;
  	}
docs: Clips the current image by modifying it in-place
  
  @method clip
  @param {int} x Starting x-coordinate
  @param {int} y Starting y-coordinate
  @param {int} width Width of area relative to starting coordinate
  @param {int} height Height of area relative to starting coordinate