code: function(callback) {
  		
  		if(!this.ifLoad) {
  			this.history.push('add to stack task: jpegToData');
  			this.stack(this.jpegToData, callback);
  			return;
  		} 
  		
  		var that = this;
  		
  		this.history.push('jpeg decode');
  		var jpeg = new this.jpeg_node();
  
  		jpeg.parse(new Uint8Array(this.data));
  		jpeg.decode(function(pixels) {
  			that.width = jpeg.width;
  			that.height = jpeg.height;
  			that.bpp = 4;
  			that.data = pixels;
  			callback.call(that);
  		});
  	}
docs: jpegToData(function callback)
  
  Decoding JPEG image to the palette.
  @param callback - call function after decoding.