code: protected void readGraphicControlExt() throws IOException {
          in.read();    // block size
          int packed = in.read();   // packed fields
          dispose = (packed & 0x1c) >> 2;   // disposal method
          if (dispose == 0) {
          	// elect to keep old image if discretionary
          	dispose = 1;   
          }
          transparency = (packed & 1) != 0;
          delay = readShort() * 10;   // delay in milliseconds
          transIndex = in.read();        // transparent color index
          in.read();                     // block terminator
      }
docs: Reads Graphics Control Extension values