anchor.diff:    }
   
     Uint8List _lastImage;
  +  int _lastImageDuration;
     NeuralQuantizer _lastColorMap;
     int _width;
     int _height;
  
positive.code: 
      _lastColorMap = NeuralQuantizer(image, samplingFactor: samplingFactor);
      _lastImage = _lastColorMap.getIndexMap(image);
    }
  
    /// Encode the images that were added with [addFrame].
  
negative.code:         0 | // 7   user input - 0 = none
          transparency); // 8   transparency flag
  
      output.writeUint16(_lastImageDuration ?? delay); // delay x 1/100 sec
      output.writeByte(0); // transparent color index
      output.writeByte(0); // block terminator
    }
  