anchor.diff:          ImprovedByteBuilder builder = new ImprovedByteBuilder();
   
           this.header(builder);
  +
  +        // image
           this.writeIHDR(builder);
  +        this.writeIDAT(builder);
  +        this.writeIEND(builder);
   
           return builder.toBuffer();
       }
  
positive.code:             ..appendInt32(imageSource.width)
              ..appendInt32(imageSource.height)
              ..appendByte(8) // 8 bits per channel
              ..appendByte(2)//6) // truecolour with alpha
              ..appendByte(0) // compression mode 0, as per spec
              ..appendByte(0) // filter mode 0, as per spec
              ..appendByte(0) // no interlace
          ;
  
          writeDataToBlocks(builder, "IHDR", ihdr.toBuffer());
      }
  
      //################################## block writing methods
  
negative.code:         }
      }
  
      //################################## image
  
      ByteBuffer processImage() {
          
      }
  
      //################################## test stuff
  
      void testBlockWriting(ImprovedByteBuilder builder) {
  