code: function writeImageDesc() {
  
      out.writeByte(0x2c); // image separator
      WriteShort(0); // image position x,y = 0,0
      WriteShort(0);
      WriteShort(width); // image size
      WriteShort(height);
  
      // packed fields
      if (firstFrame) {
        // no LCT - GCT is used for first (or only) frame
        out.writeByte(0);
      } else {
        // specify normal LCT
        out.writeByte(0x80 | // 1 local color table 1=yes
          0 | // 2 interlace - 0=no
          0 | // 3 sorted - 0=no
          0 | // 4-5 reserved
          palSize); // 6-8 size of color table
      }
    }
docs: Writes Image Descriptor