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authorThomas Groman <tgroman@nuegia.net>2020-04-20 20:56:28 -0700
committerThomas Groman <tgroman@nuegia.net>2020-04-20 20:56:28 -0700
commit508d270a4d78d491bbe1c67c309c404f547da58a (patch)
treed16e2a906501dcda7b4d268579896f03e125f553 /build/pypng/pngchunk
parentf9cab004186edb425a9b88ad649726605080a17c (diff)
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+#!/usr/bin/env python
+# $URL: http://pypng.googlecode.com/svn/trunk/code/pngchunk $
+# $Rev: 156 $
+# pngchunk
+# Chunk editing/extraction tool.
+
+import struct
+import warnings
+
+# Local module.
+import png
+
+"""
+pngchunk [--gamma g] [--iccprofile file] [--sigbit b] [-c cHNK!] [-c cHNK:foo] [-c cHNK<file]
+
+The ``-c`` option is used to add or remove chunks. A chunk is specified
+by its 4 byte chunk type. If this is followed by a ``!`` then that
+chunk is removed from the PNG file. If the chunk type is followed by a
+``:`` then the chunk is replaced with the contents of the rest of the
+argument (this is probably only useful if the content is mostly ASCII,
+otherwise it's a pain to quote the contents, otherwise see...). A ``<``
+can be used to take the contents of the chunk from the named file.
+"""
+
+
+def chunk(out, inp, l):
+ """Process the input PNG file to the output, chunk by chunk. Chunks
+ can be inserted, removed, replaced, or sometimes edited. Generally,
+ chunks are not inspected, so pixel data (in the ``IDAT`` chunks)
+ cannot be modified. `l` should be a list of (*chunktype*,
+ *content*) pairs. *chunktype* is usually the type of the PNG chunk,
+ specified as a 4-byte Python string, and *content* is the chunk's
+ content, also as a string; if *content* is ``None`` then *all*
+ chunks of that type will be removed.
+
+ This function *knows* about certain chunk types and will
+ automatically convert from Python friendly representations to
+ string-of-bytes.
+
+ chunktype
+ 'gamma' 'gAMA' float
+ 'sigbit' 'sBIT' int, or tuple of length 1,2 or 3
+
+ Note that the length of the strings used to identify *friendly*
+ chunk types is greater than 4, hence they cannot be confused with
+ canonical chunk types.
+
+ Chunk types, if specified using the 4-byte syntax, need not be
+ official PNG chunks at all. Non-standard chunks can be created.
+ """
+
+ def canonical(p):
+ """Take a pair (*chunktype*, *content*), and return canonical
+ representation (*chunktype*, *content*) where `chunktype` is the
+ 4-byte PNG chunk type and `content` is a string.
+ """
+
+ t,v = p
+ if len(t) == 4:
+ return t,v
+ if t == 'gamma':
+ t = 'gAMA'
+ v = int(round(1e5*v))
+ v = struct.pack('>I', v)
+ elif t == 'sigbit':
+ t = 'sBIT'
+ try:
+ v[0]
+ except TypeError:
+ v = (v,)
+ v = struct.pack('%dB' % len(v), *v)
+ elif t == 'iccprofile':
+ t = 'iCCP'
+ # http://www.w3.org/TR/PNG/#11iCCP
+ v = 'a color profile\x00\x00' + v.encode('zip')
+ else:
+ warnings.warn('Unknown chunk type %r' % t)
+ return t[:4],v
+
+ l = map(canonical, l)
+ # Some chunks automagically replace ones that are present in the
+ # source PNG. There can only be one of each of these chunk types.
+ # Create a 'replace' dictionary to record these chunks.
+ add = []
+ delete = set()
+ replacing = set(['gAMA', 'sBIT', 'PLTE', 'tRNS', 'sPLT', 'IHDR'])
+ replace = dict()
+ for t,v in l:
+ if v is None:
+ delete.add(t)
+ elif t in replacing:
+ replace[t] = v
+ else:
+ add.append((t,v))
+ del l
+ r = png.Reader(file=inp)
+ chunks = r.chunks()
+ def iterchunks():
+ for t,v in chunks:
+ if t in delete:
+ continue
+ if t in replace:
+ yield t,replace[t]
+ del replace[t]
+ continue
+ if t == 'IDAT' and replace:
+ # Insert into the output any chunks that are on the
+ # replace list. We haven't output them yet, because we
+ # didn't see an original chunk of the same type to
+ # replace. Thus the "replace" is actually an "insert".
+ for u,w in replace.items():
+ yield u,w
+ del replace[u]
+ if t == 'IDAT' and add:
+ for item in add:
+ yield item
+ del add[:]
+ yield t,v
+ return png.write_chunks(out, iterchunks())
+
+class Usage(Exception):
+ pass
+
+def main(argv=None):
+ import getopt
+ import re
+ import sys
+
+ if argv is None:
+ argv = sys.argv
+
+ argv = argv[1:]
+
+ try:
+ try:
+ opt,arg = getopt.getopt(argv, 'c:',
+ ['gamma=', 'iccprofile=', 'sigbit='])
+ except getopt.error, msg:
+ raise Usage(msg)
+ k = []
+ for o,v in opt:
+ if o in ['--gamma']:
+ k.append(('gamma', float(v)))
+ if o in ['--sigbit']:
+ k.append(('sigbit', int(v)))
+ if o in ['--iccprofile']:
+ k.append(('iccprofile', open(v, 'rb').read()))
+ if o in ['-c']:
+ type = v[:4]
+ if not re.match('[a-zA-Z]{4}', type):
+ raise Usage('Chunk type must consist of 4 letters.')
+ if v[4] == '!':
+ k.append((type, None))
+ if v[4] == ':':
+ k.append((type, v[5:]))
+ if v[4] == '<':
+ k.append((type, open(v[5:], 'rb').read()))
+ except Usage, err:
+ print >>sys.stderr, (
+ "usage: pngchunk [--gamma d.dd] [--sigbit b] [-c cHNK! | -c cHNK:text-string]")
+ print >>sys.stderr, err.message
+ return 2
+
+ if len(arg) > 0:
+ f = open(arg[0], 'rb')
+ else:
+ f = sys.stdin
+ return chunk(sys.stdout, f, k)
+
+
+if __name__ == '__main__':
+ main()