code: function(callback) {
  		
  		if(!this.ifLoad) {
  			this.stack(this.pngToData, callback);
  			return;
  		}
  		
  		this.history.push('png decode');
  		
  		var that = this;
  		
  		var png = new this.png_node(this.data);
  		png.decode(function (pixels) {
  			
  			that.width = png.width;
  			that.height = png.height;
  			that.data = pixels;
  			that.bpp = 4;
  			callback.call(that);
  		});
  		
  		return;		
  	}
docs: pngToData(function callback)
  
  Decoding PNG image to the palette.
  @param callback - call function after decoding.