#!/usr/bin/python # tz_png.py # --copyright-- Copyright 2007 (C) Tranzoa, Co. All rights reserved. Warranty: You're free and on your own here. This code is not necessarily up-to-date or of public quality. # --url-- http://www.tranzoa.net/tzpython/ # --email-- pycode is the name to send to. tranzoa.com is the place to send to. # --bodstamps-- # May 17, 2007 bar # June 26, 2007 bar fix error conditions # November 18, 2007 bar turn on doxygen # November 20, 2007 bar comments # November 27, 2007 bar insert boilerplate copyright # January 26, 2008 bar allow a zero chunk crc (spurious error one night - from a file I generated using wxwidgets) # May 17, 2008 bar email adr # --eodstamps-- ## \file # # # Do what I need to do with .png files. # # http://www.w3.org/TR/PNG/ # # import time import replace_file import tzlib ## The start of a .png file PNG_MAGIC_BYTES = "\x89PNG\r\n\x1A\n" ## Keywords in .png comments PNG_KEYWORDS = [ "Title", # Short (one line) title or caption for image "Author", # Name of image's creator "Description", # Description of image (possibly long) "Copyright", # Copyright notice "Creation Time", # Time of original image creation "Software", # Software used to create the image "Disclaimer", # Legal disclaimer "Warning", # Warning of nature of content "Source", # Device used to create the image "Comment", # Miscellaneous comment ] # # Note: this table is, in fact, that of tzlib's crc32.c, as opposed to pkcrc.c. # ## A .png CRC table is created (which we could simply copy the data from crc32.c) crc_table = [ 0L ] * 256 for n in xrange(len(crc_table)) : c = n; for k in xrange(8) : if c & 1 : c = 0xedb88320L ^ (c >> 1) else : c = c >> 1 pass crc_table[n] = c def blkcrc(crc, blk, start = 0, end = 0) : """ Return the CRC of the given data starting from the given CRC. """ end = end or len(blk) for i in xrange(start, end) : crc = crc_table[(crc ^ ord(blk[i])) & 0xff] ^ (crc >> 8) return(crc & 0xFFFFffffL) class a_png_chunk : """ Class whose objects contain .png file chunks. """ def __init__(me, data, tag = "", start = 0, end = None) : """ Constructor. """ end = end or len(data) if not tag : ln = (long(ord(data[start])) << 24) | (ord(data[start + 1]) << 16) | (ord(data[start + 2]) << 8) | ord(data[start + 3]) if start + 12 + ln > end : raise ValueError("PNG chunk length too big. Offset:%u length:%u end:%u !" % ( start, ln, end ) ) me.tag = data[start + 4 : start + 8] i = start + 8 + ln me.data = data[start + 8 : i] me.crc = (ord(data[i]) << 24) | (ord(data[i + 1]) << 16) | (ord(data[i + 2]) << 8) | ord(data[i + 3]) crc = blkcrc(0xFFFFffffL, me.tag) crc = blkcrc(crc, me.data) crc = (~crc) & 0xFFFFffffL if not me.crc : me.crc = crc # oh, what the heck. Something seemed to have created a zero CRC late one night. elif crc != me.crc : raise ValueError("PNG chunk tagged, %s, CRC bad %08x is not %08x!" % ( str(tzlib.ascii(me.tag)), me.crc, crc ) ) pass elif len(tag) == 4 : me.tag = tag me.data = data me.crc = blkcrc(0xFFFFffffL, me.tag) me.crc = blkcrc(me.crc, me.data) me.crc = (~me.crc) & 0xFFFFffffL else : raise ValueError("Making PNG bad tag chunk [%s]!" % ( str(tag) ) ) pass pass # a_png_chunk class a_png_tEXt_chunk(a_png_chunk) : """ Class whose objects contain tEXt chunks. """ def __init__(me, key, arg) : """ Constructor. """ if not key : raise ValueError("No key for PNG tEXt chunk!") if len(key) > 79 : raise IndexError("PNG key too long for tEXt cunk!") a_png_chunk.__init__(me, key + "\0" + arg, tag = "tEXt") pass class a_png : """ Class whose objects are .png file data. """ def __init__(me, fi) : """ Constructor. """ me.chunks = [] if fi : fn = None if isinstance(fi, basestring) : fn = fi fi = open(fi, "rb") es = "" me.all = fi.read() if fn : fi.close() es = fn if not me.all.startswith(PNG_MAGIC_BYTES) : raise ValueError("File %s not a .png file!" % ( es ) ) i = 8 while i < len(me.all) : me.chunks.append(a_png_chunk(me.all, None, i, len(me.all))) i += len(me.chunks[-1].data) + 12 if len(me.chunks) < 3 : raise ValueError("Not enough chunks in .png file: %s!" % ( es ) ) if me.chunks[0].tag != 'IHDR' : raise ValueError("First .png file chunk not IHDR (%s) in file: %s!" % ( me.chunks[0].tag, es ) ) if me.chunks[-1].tag != 'IEND' : raise ValueError("Last .png file chunk not IEND (%s) in file: %s!" % ( me.chunks[-1].tag, es ) ) pass pass def insert_tIME(me, t = None) : """ Put a tIME chunk in the .png data. """ if not t : t = time.time() t = time.gmtime(t) d = chr((t.tm_year >> 8) & 0xff) + chr(t.tm_year & 0xff) + chr(t.tm_mon) + chr(t.tm_mday) + chr(t.tm_hour) + chr(t.tm_min) + chr(t.tm_sec) c = a_png_chunk(d, "tIME") for i in xrange(len(me.chunks)) : if me.chunks[i].tag == "tIME" : del(me.chunks[i]) break pass me.chunks.insert(1, c) def save(me, fn) : """ Save the .png to the named file. """ tfn = fn + ".tmp" fo = open(tfn, "wb") fo.write(PNG_MAGIC_BYTES) for c in me.chunks : fo.write(chr((len(c.data) >> 24) & 0xff) + chr((len(c.data) >> 16) & 0xff) + chr((len(c.data) >> 8) & 0xff) + chr(len(c.data) & 0xff)) fo.write(c.tag) fo.write(c.data) fo.write(chr((c.crc >> 24) & 0xff) + chr((c.crc >> 16) & 0xff) + chr((c.crc >> 8) & 0xff) + chr(c.crc & 0xff)) fo.close() del(fo) replace_file.replace_file(fn, tfn, fn + ".bak") pass # a_png if __name__ == '__main__' : import sys import TZCommandLineAtFile del(sys.argv[0]) TZCommandLineAtFile.expand_at_sign_command_line_files(sys.argv) while len(sys.argv) : fn = sys.argv.pop(0) png = a_png(fn) print fn, len(png.chunks) png.chunks.insert(-1, a_png_tEXt_chunk("Comment", "blah blah")) png.chunks.insert(-1, a_png_tEXt_chunk("Creation Time", "May 18, 2007")) png.insert_tIME() c = png.chunks.pop(-1) png.chunks.append(a_png_chunk(c.data, c.tag)) c = png.chunks.pop(0) png.chunks.insert(0, a_png_chunk(c.data, c.tag)) png.save(fn + "_n.png") pass # # # # eof