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The datpng header looks like this:

| ver |  length   |   width   | data ...
|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|
0  1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 

struct datpng_header
{
  word  ver;
  dword length;
  dword width;
  byte  c;
  byte  d;
}

All header data is stored in big endian (network) order.

  ver
  ---
The 'ver' bytes are the version of the data PNG file. This version
indicates the encoded bit depth, existance of a checksum, and other
features.

The least significant 4 bits define the bit depth (up to 16). The most
significant bit (the sign bit) indicates a checksum. All other bits
describe a version of the datpng. This will allow future versions of
the program to continue processing older datpng files.

  length
  ------
The 'length' bytes give the length of the data in bytes.

  width
  -----
The 'width' bytes give the width of the data chunk in pixels.