code: protected void readLSD() throws IOException {
          
          // logical screen size
          width = readShort();
          height = readShort();
          
          // packed fields
          int packed = in.read();
          gctFlag = (packed & 0x80) != 0;      // 1   : global color table flag
          m_gbpc = (packed & 7) + 1;
          bgIndex = in.read();        // background color index
          pixelAspect = in.read();    // pixel aspect ratio
      }
docs: Reads Logical Screen Descriptor