#
# The Python Imaging Library.
# $Id$
#
# PNG support code
#
# See "PNG (Portable Network Graphics) Specification, version 1.0;
# W3C Recommendation", 1996-10-01, Thomas Boutell (ed.).
#
# history:
# 1996-05-06 fl Created (couldn't resist it)
# 1996-12-14 fl Upgraded, added read and verify support (0.2)
# 1996-12-15 fl Separate PNG stream parser
# 1996-12-29 fl Added write support, added getchunks
# 1996-12-30 fl Eliminated circular references in decoder (0.3)
# 1998-07-12 fl Read/write 16-bit images as mode I (0.4)
# 2001-02-08 fl Added transparency support (from Zircon) (0.5)
# 2001-04-16 fl Don't close data source in "open" method (0.6)
# 2004-02-24 fl Don't even pretend to support interlaced files (0.7)
# 2004-08-31 fl Do basic sanity check on chunk identifiers (0.8)
# 2004-09-20 fl Added PngInfo chunk container
# 2004-12-18 fl Added DPI read support (based on code by Niki Spahiev)
# 2008-08-13 fl Added tRNS support for RGB images
# 2009-03-06 fl Support for preserving ICC profiles (by Florian Hoech)
# 2009-03-08 fl Added zTXT support (from Lowell Alleman)
# 2009-03-29 fl Read interlaced PNG files (from Conrado Porto Lopes Gouvua)
#
# Copyright (c) 1997-2009 by Secret Labs AB
# Copyright (c) 1996 by Fredrik Lundh
#
# See the README file for information on usage and redistribution.
#
__version__ = "0.9"
import re, string
import Image, ImageFile, ImagePalette, zlib
def i16(c):
return ord(c[1]) + (ord(c[0])<<8)
def i32(c):
return ord(c[3]) + (ord(c[2])<<8) + (ord(c[1])<<16) + (ord(c[0])<<24)
is_cid = re.compile("\w\w\w\w").match
_MAGIC = "\211PNG\r\n\032\n"
_MODES = {
# supported bits/color combinations, and corresponding modes/rawmodes
(1, 0): ("1", "1"),
(2, 0): ("L", "L;2"),
(4, 0): ("L", "L;4"),
(8, 0): ("L", "L"),
(16,0): ("I", "I;16B"),
(8, 2): ("RGB", "RGB"),
(16,2): ("RGB", "RGB;16B"),
(1, 3): ("P", "P;1"),
(2, 3): ("P", "P;2"),
(4, 3): ("P", "P;4"),
(8, 3): ("P", "P"),
(8, 4): ("LA", "LA"),
(16,4): ("RGBA", "LA;16B"), # LA;16B->LA not yet available
(8, 6): ("RGBA", "RGBA"),
(16,6): ("RGBA", "RGBA;16B"),
}
# --------------------------------------------------------------------
# Support classes. Suitable for PNG and related formats like MNG etc.
class ChunkStream:
def __init__(self, fp):
self.fp = fp
self.queue = []
if not hasattr(Image.core, "crc32"):
self.crc = self.crc_skip
def read(self):
"Fetch a new chunk. Returns header information."
if self.queue:
cid, pos, len = self.queue[-1]
del self.queue[-1]
self.fp.seek(pos)
else:
s = self.fp.read(8)
cid = s[4:]
pos = self.fp.tell()
len = i32(s)
if not is_cid(cid):
raise SyntaxError, "broken PNG file (chunk %s)" % repr(cid)
return cid, pos, len
def close(self):
self.queue = self.crc = self.fp = None
def push(self, cid, pos, len):
self.queue.append((cid, pos, len))
def call(self, cid, pos, len):
"Call the appropriate chunk handler"
if Image.DEBUG:
print "STREAM", cid, pos, len
return getattr(self, "chunk_" + cid)(pos, len)
def crc(self, cid, data):
"Read and verify checksum"
crc1 = Image.core.crc32(data, Image.core.crc32(cid))
crc2 = i16(self.fp.read(2)), i16(self.fp.read(2))
if crc1 != crc2:
raise SyntaxError, "broken PNG file"\
"(bad header checksum in %s)" % cid
def crc_skip(self, cid, data):
"Read checksum. Used if the C module is not present"
self.fp.read(4)
def verify(self, endchunk = "IEND"):
# Simple approach; just calculate checksum for all remaining
# blocks. Must be called directly after open.
cids = []
while 1:
cid, pos, len = self.read()
if cid == endchunk:
break
self.crc(cid, ImageFile._safe_read(self.fp, len))
cids.append(cid)
return cids
# --------------------------------------------------------------------
# PNG chunk container (for use with save(pnginfo=))
class PngInfo:
def __init__(self):
self.chunks = []
def add(self, cid, data):
self.chunks.append((cid, data))
def add_text(self, key, value, zip=0):
if zip:
import zlib
self.add("zTXt", key + "\0\0" + zlib.compress(value))
else:
self.add("tEXt", key + "\0" + value)
# --------------------------------------------------------------------
# PNG image stream (IHDR/IEND)
class PngStream(ChunkStream):
def __init__(self, fp):
ChunkStream.__init__(self, fp)
# local copies of Image attributes
self.im_info = {}
self.im_text = {}
self.im_size = (0,0)
self.im_mode = None
self.im_tile = None
self.im_palette = None
def chunk_iCCP(self, pos, len):
# ICC profile
s = ImageFile._safe_read(self.fp, len)
# according to PNG spec, the iCCP chunk contains:
# Profile name 1-79 bytes (character string)
# Null separator 1 byte (null character)
# Compression method 1 byte (0)
# Compressed profile n bytes (zlib with deflate compression)
i = string.find(s, chr(0))
if Image.DEBUG:
print "iCCP profile name", s[:i]
print "Compression method", ord(s[i])
comp_method = ord(s[i])
if comp_method != 0:
raise SyntaxError("Unknown compression method %s in iCCP chunk" % comp_method)
try:
icc_profile = zlib.decompress(s[i+2:])
except zlib.error:
icc_profile = None # FIXME
self.im_info["icc_profile"] = icc_profile
return s
def chunk_IHDR(self, pos, len):
# image header
s = ImageFile._safe_read(self.fp, len)
self.im_size = i32(s), i32(s[4:])
try:
self.im_mode, self.im_rawmode = _MODES[(ord(s[8]), ord(s[9]))]
except:
pass
if ord(s[12]):
self.im_info["interlace"] = 1
if ord(s[11]):
raise SyntaxError, "unknown filter category"
return s
def chunk_IDAT(self, pos, len):
# image data
self.im_tile = [("zip", (0,0)+self.im_size, pos, self.im_rawmode)]
self.im_idat = len
raise EOFError
def chunk_IEND(self, pos, len):
# end of PNG image
raise EOFError
def chunk_PLTE(self, pos, len):
# palette
s = ImageFile._safe_read(self.fp, len)
if self.im_mode == "P":
self.im_palette = "RGB", s
return s
def chunk_tRNS(self, pos, len):
# transparency
s = ImageFile._safe_read(self.fp, len)
if self.im_mode == "P":
i = string.find(s, chr(0))
if i >= 0:
self.im_info["transparency"] = i
elif self.im_mode == "L":
self.im_info["transparency"] = i16(s)
elif self.im_mode == "RGB":
self.im_info["transparency"] = i16(s), i16(s[2:]), i16(s[4:])
return s
def chunk_gAMA(self, pos, len):
# gamma setting
s = ImageFile._safe_read(self.fp, len)
self.im_info["gamma"] = i32(s) / 100000.0
return s
def chunk_pHYs(self, pos, len):
# pixels per unit
s = ImageFile._safe_read(self.fp, len)
px, py = i32(s), i32(s[4:])
unit = ord(s[8])
if unit == 1: # meter
dpi = int(px * 0.0254 + 0.5), int(py * 0.0254 + 0.5)
self.im_info["dpi"] = dpi
elif unit == 0:
self.im_info["aspect"] = px, py
return s
def chunk_tEXt(self, pos, len):
# text
s = ImageFile._safe_read(self.fp, len)
try:
k, v = string.split(s, "\0", 1)
except ValueError:
k = s; v = "" # fallback for broken tEXt tags
if k:
self.im_info[k] = self.im_text[k] = v
return s
def chunk_zTXt(self, pos, len):
# compressed text
s = ImageFile._safe_read(self.fp, len)
k, v = string.split(s, "\0", 1)
comp_method = ord(v[0])
if comp_method != 0:
raise SyntaxError("Unknown compression method %s in zTXt chunk" % comp_method)
import zlib
self.im_info[k] = self.im_text[k] = zlib.decompress(v[1:])
return s
# --------------------------------------------------------------------
# PNG reader
def _accept(prefix):
return prefix[:8] == _MAGIC
##
# Image plugin for PNG images.
class PngImageFile(ImageFile.ImageFile):
format = "PNG"
format_description = "Portable network graphics"
def _open(self):
if self.fp.read(8) != _MAGIC:
raise SyntaxError, "not a PNG file"
#
# Parse headers up to the first IDAT chunk
self.png = PngStream(self.fp)
while 1:
#
# get next chunk
cid, pos, len = self.png.read()
try:
s = self.png.call(cid, pos, len)
except EOFError:
break
except AttributeError:
if Image.DEBUG:
print cid, pos, len, "(unknown)"
s = ImageFile._safe_read(self.fp, len)
self.png.crc(cid, s)
#
# Copy relevant attributes from the PngStream. An alternative
# would be to let the PngStream class modify these attributes
# directly, but that introduces circular references which are
# difficult to break if things go wrong in the decoder...
# (believe me, I've tried ;-)
self.mode = self.png.im_mode
self.size = self.png.im_size
self.info = self.png.im_info
self.text = self.png.im_text # experimental
self.tile = self.png.im_tile
if self.png.im_palette:
rawmode, data = self.png.im_palette
self.palette = ImagePalette.raw(rawmode, data)
self.__idat = len # used by load_read()
def verify(self):
"Verify PNG file"
if self.fp is None:
raise RuntimeError("verify must be called directly after open")
# back up to beginning of IDAT block
self.fp.seek(self.tile[0][2] - 8)
self.png.verify()
self.png.close()
self.fp = None
def load_prepare(self):
"internal: prepare to read PNG file"
if self.info.get("interlace"):
self.decoderconfig = self.decoderconfig + (1,)
ImageFile.ImageFile.load_prepare(self)
def load_read(self, bytes):
"internal: read more image data"
while self.__idat == 0:
# end of chunk, skip forward to next one
self.fp.read(4) # CRC
cid, pos, len = self.png.read()
if cid not in ["IDAT", "DDAT"]:
self.png.push(cid, pos, len)
return ""
self.__idat = len # empty chunks are allowed
# read more data from this chunk
if bytes <= 0:
bytes = self.__idat
else:
bytes = min(bytes, self.__idat)
self.__idat = self.__idat - bytes
return self.fp.read(bytes)
def load_end(self):
"internal: finished reading image data"
self.png.close()
self.png = None
# --------------------------------------------------------------------
# PNG writer
def o16(i):
return chr(i>>8&255) + chr(i&255)
def o32(i):
return chr(i>>24&255) + chr(i>>16&255) + chr(i>>8&255) + chr(i&255)
_OUTMODES = {
# supported PIL modes, and corresponding rawmodes/bits/color combinations
"1": ("1", chr(1)+chr(0)),
"L;1": ("L;1", chr(1)+chr(0)),
"L;2": ("L;2", chr(2)+chr(0)),
"L;4": ("L;4", chr(4)+chr(0)),
"L": ("L", chr(8)+chr(0)),
"LA": ("LA", chr(8)+chr(4)),
"I": ("I;16B", chr(16)+chr(0)),
"P;1": ("P;1", chr(1)+chr(3)),
"P;2": ("P;2", chr(2)+chr(3)),
"P;4": ("P;4", chr(4)+chr(3)),
"P": ("P", chr(8)+chr(3)),
"RGB": ("RGB", chr(8)+chr(2)),
"RGBA":("RGBA", chr(8)+chr(6)),
}
def putchunk(fp, cid, *data):
"Write a PNG chunk (including CRC field)"
data = string.join(data, "")
fp.write(o32(len(data)) + cid)
fp.write(data)
hi, lo = Image.core.crc32(data, Image.core.crc32(cid))
fp.write(o16(hi) + o16(lo))
class _idat:
# wrap output from the encoder in IDAT chunks
def __init__(self, fp, chunk):
self.fp = fp
self.chunk = chunk
def write(self, data):
self.chunk(self.fp, "IDAT", data)
def _save(im, fp, filename, chunk=putchunk, check=0):
# save an image to disk (called by the save method)
mode = im.mode
if mode == "P":
#
# attempt to minimize storage requirements for palette images
if im.encoderinfo.has_key("bits"):
# number of bits specified by user
n = 1 << im.encoderinfo["bits"]
else:
# check palette contents
n = 256 # FIXME
if n <= 2:
bits = 1
elif n <= 4:
bits = 2
elif n <= 16:
bits = 4
else:
bits = 8
if bits != 8:
mode = "%s;%d" % (mode, bits)
# encoder options
if im.encoderinfo.has_key("dictionary"):
dictionary = im.encoderinfo["dictionary"]
else:
dictionary = ""
im.encoderconfig = (im.encoderinfo.has_key("optimize"), dictionary)
# get the corresponding PNG mode
try:
rawmode, mode = _OUTMODES[mode]
except KeyError:
raise IOError, "cannot write mode %s as PNG" % mode
if check:
return check
#
# write minimal PNG file
fp.write(_MAGIC)
chunk(fp, "IHDR",
o32(im.size[0]), o32(im.size[1]), # 0: size
mode, # 8: depth/type
chr(0), # 10: compression
chr(0), # 11: filter category
chr(0)) # 12: interlace flag
if im.mode == "P":
chunk(fp, "PLTE", im.im.getpalette("RGB"))
if im.encoderinfo.has_key("transparency"):
if im.mode == "P":
transparency = max(0, min(255, im.encoderinfo["transparency"]))
chunk(fp, "tRNS", chr(255) * transparency + chr(0))
elif im.mode == "L":
transparency = max(0, min(65535, im.encoderinfo["transparency"]))
chunk(fp, "tRNS", o16(transparency))
elif im.mode == "RGB":
red, green, blue = im.encoderinfo["transparency"]
chunk(fp, "tRNS", o16(red) + o16(green) + o16(blue))
else:
raise IOError("cannot use transparency for this mode")
if 0:
# FIXME: to be supported some day
chunk(fp, "gAMA", o32(int(gamma * 100000.0)))
dpi = im.encoderinfo.get("dpi")
if dpi:
chunk(fp, "pHYs",
o32(int(dpi[0] / 0.0254 + 0.5)),
o32(int(dpi[1] / 0.0254 + 0.5)),
chr(1))
info = im.encoderinfo.get("pnginfo")
if info:
for cid, data in info.chunks:
chunk(fp, cid, data)
# ICC profile writing support -- 2008-06-06 Florian Hoech
if im.info.has_key("icc_profile"):
# ICC profile
# according to PNG spec, the iCCP chunk contains:
# Profile name 1-79 bytes (character string)
# Null separator 1 byte (null character)
# Compression method 1 byte (0)
# Compressed profile n bytes (zlib with deflate compression)
try:
import ICCProfile
p = ICCProfile.ICCProfile(im.info["icc_profile"])
name = p.tags.desc.get("ASCII", p.tags.desc.get("Unicode", p.tags.desc.get("Macintosh", p.tags.desc.get("en", {}).get("US", "ICC Profile")))).encode("latin1", "replace")[:79]
except ImportError:
name = "ICC Profile"
data = name + "\0\0" + zlib.compress(im.info["icc_profile"])
chunk(fp, "iCCP", data)
ImageFile._save(im, _idat(fp, chunk), [("zip", (0,0)+im.size, 0, rawmode)])
chunk(fp, "IEND", "")
try:
fp.flush()
except:
pass
# --------------------------------------------------------------------
# PNG chunk converter
def getchunks(im, **params):
"""Return a list of PNG chunks representing this image."""
class collector:
data = []
def write(self, data):
pass
def append(self, chunk):
self.data.append(chunk)
def append(fp, cid, *data):
data = string.join(data, "")
hi, lo = Image.core.crc32(data, Image.core.crc32(cid))
crc = o16(hi) + o16(lo)
fp.append((cid, data, crc))
fp = collector()
try:
im.encoderinfo = params
_save(im, fp, None, append)
finally:
del im.encoderinfo
return fp.data
# --------------------------------------------------------------------
# Registry
Image.register_open("PNG", PngImageFile, _accept)
Image.register_save("PNG", _save)
Image.register_extension("PNG", ".png")
Image.register_mime("PNG", "image/png")
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