PNG Datatype Handler - (c) Simon Clarke 1996-7
==============================================

Here is a datatype encoder/decoder based upon libpng and zlib.  It can
read and write the royality free PNG format images.

The PNG format is an excellent loss-less format that can replace and 
improve formats like GIF and common uses of TIFF.  Sampling depths can
be from 1 to 16 bits, it supports indexed-palette, true colour and
grayscale images with an optional alpha channel. It is now an Internet 
standard.  For more information please look at http://www.wco.com/~png

N.B. When you pass 8 bit data to the convert to the PNG format, the
datatype will use the system_colors()->color_list to expand the data
into 24 bit.

If there is an PNG colour format this handler does not support properly,
I would be very grateful if you would send me the offending image.  There
are still probably many problems with this handler, mainly because
libpng is a bit buggy, but please send in bug reports!

History
=======

1.00 - 	Inital Release

1.11 -	Fixed bug that caused problems with palette.  Thanks to Philippe
		Thomas for the bug report.  
		Fixed really stupid bug that caused images with a depth lower than
		4 bits per component to crash - thanks again to Philippe Thomas for 
		the bug report.  
		Added progressive and PNG`s own Adam7 interlace format support
		through the MEDIAStream format.  If you want your application to 
		support this, please request the image as a DATA_MEDIA, be 
		prepared for this to fail and to re-request as a DATA_BITMAP.
		Added interlace and more depth options to preference view.
		Fixed grayscale images, they are now returned as a B_RGB_32_BIT 
		bitmap.
		Linked against latest libpng 0.96 and zlib 1.0.4.
		DR9 AA version.  Better error handling.  Additional type checking in
		Identify() function.  Fixed 8 bit input data for save routine.
		Added some text comments to images.
		
1.15 -	Changed standard output to be written in steps.  Fixed 8-bit output
		of images  (Thanks to Edmund Vermeulen for the report).  Fixed
		memory leak in progressive code.  Ported to DR9 Preview and 
		Datatypes 1.6.1. Added extra output depths

Next Versions
=============
Quicker saving of images.

Special Thanks To
=================
Jon Watte, Jeremy Moskovish, Philippe Thomas and Edmund Vermeulen.

License
=======
There is no warranty with this program, and no liability for any consequential
damages caused arising out of the use or inability to use this program.  In no
event shall I be liable for any damages whatsoever.
Distribution is strictly forbidden on any kind of media containing commerical
software without a license agreement.  Distribution is also forbidden on any
software collections costing over 50USD.

Contact
=======
Simon Clarke (S.J.Clarke@herts.ac.uk)
If you want to include this with a commerical program, please email me.