anchor.diff:      const initCodeSize = 8;
       output!.writeByte(initCodeSize);
   
  -    final hTab = Int32List(HSIZE);
  -    final codeTab = Int32List(HSIZE);
  +    final hTab = Int32List(_hsize);
  +    final codeTab = Int32List(_hsize);
       var remaining = width * height;
       var curPixel = 0;
   
  
positive.code: 
      int _nextPixel() {
        if (remaining == 0) {
          return EOF;
        }
        --remaining;
        return image![curPixel++] & 0xff;
  
negative.code:   void _addImage(Uint8List? image, int width, int height, Uint8List colorMap,
        int numColors) {
      // Image desc
      output!.writeByte(_imageDescRecordType);
      output!.writeUint16(0); // image position x,y = 0,0
      output!.writeUint16(0);
      output!.writeUint16(width); // image size
  