README

		sng -- a compiler for an editable PNG representation

SNG (Scriptable Network Graphics) is a minilanguage designed to
reflect the data and structure of PNG (Portable Network Graphics)
files in an editable form.  

The sng program translates between SNG and PNG.  It can be useful
especially for viewing and editing data in obscure ancillary chanks
that graphics editors won't handle.  Also, since SNG is easy to
generate from scripts, sng may be useful at the end of a pipeline that
programmatically generates PNG images.

This program requires libpng-1.0.9beta7 or later.  All these should be
handled correctly with 1.0.9 final; however the default build of 1.0.9
doesn't support the iTXT chunk correctly, so sng won't either.  With
the 1.1.x version of libpng, all chunks including iTXT are handled
correctly.

For more details, consult the manual page.  Files in this distribution:

README		this file
Makefile	Makefile for building sng
sng.h		common declarations for compiler and decompiler
main.c		handle options
sng.1		the manual page 
sngc.c		SNG to PNG compiler
sngd.c		PNG to SNG decompiler
test.sng	Test file exercising all chunk types
TODO		unfinished business
sng_regress	regression-test harness for sng

The sng code has been tested on all of the non-broken images in the PNG 
test suite at <http://www.cdrom.com/pub/png/pngsuite.html> using sng_regress.

						Eric S. Raymond
						esr@thyrsus.com
						http://www.catb.org