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Pillow/PIL/PngImagePlugin.py
Andrew Murray 1856d106ea Corrected parameters in documentation
2017-09-29 21:08:49 +10:00

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#
# 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.
#
import logging
import re
import zlib
import struct
from . import Image, ImageFile, ImagePalette
from ._binary import i8, i16be as i16, i32be as i32, o16be as o16, o32be as o32
__version__ = "0.9"
logger = logging.getLogger(__name__)
is_cid = re.compile(br"\w\w\w\w").match
_MAGIC = b"\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"),
}
_simple_palette = re.compile(b'^\xff*\x00\xff*$')
# Maximum decompressed size for a iTXt or zTXt chunk.
# Eliminates decompression bombs where compressed chunks can expand 1000x
MAX_TEXT_CHUNK = ImageFile.SAFEBLOCK
# Set the maximum total text chunk size.
MAX_TEXT_MEMORY = 64 * MAX_TEXT_CHUNK
def _safe_zlib_decompress(s):
dobj = zlib.decompressobj()
plaintext = dobj.decompress(s, MAX_TEXT_CHUNK)
if dobj.unconsumed_tail:
raise ValueError("Decompressed Data Too Large")
return plaintext
# --------------------------------------------------------------------
# Support classes. Suitable for PNG and related formats like MNG etc.
class ChunkStream(object):
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."
cid = None
if self.queue:
cid, pos, length = self.queue.pop()
self.fp.seek(pos)
else:
s = self.fp.read(8)
cid = s[4:]
pos = self.fp.tell()
length = i32(s)
if not is_cid(cid):
if not ImageFile.LOAD_TRUNCATED_IMAGES:
raise SyntaxError("broken PNG file (chunk %s)" % repr(cid))
return cid, pos, length
def close(self):
self.queue = self.crc = self.fp = None
def push(self, cid, pos, length):
self.queue.append((cid, pos, length))
def call(self, cid, pos, length):
"Call the appropriate chunk handler"
logger.debug("STREAM %r %s %s", cid, pos, length)
return getattr(self, "chunk_" + cid.decode('ascii'))(pos, length)
def crc(self, cid, data):
"Read and verify checksum"
# Skip CRC checks for ancillary chunks if allowed to load truncated images
# 5th byte of first char is 1 [specs, section 5.4]
if ImageFile.LOAD_TRUNCATED_IMAGES and (i8(cid[0]) >> 5 & 1):
self.crc_skip(cid, data)
return
try:
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 %r)"
% cid)
except struct.error:
raise SyntaxError("broken PNG file (incomplete checksum in %r)"
% 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=b"IEND"):
# Simple approach; just calculate checksum for all remaining
# blocks. Must be called directly after open.
cids = []
while True:
try:
cid, pos, length = self.read()
except struct.error:
raise IOError("truncated PNG file")
if cid == endchunk:
break
self.crc(cid, ImageFile._safe_read(self.fp, length))
cids.append(cid)
return cids
class iTXt(str):
"""
Subclass of string to allow iTXt chunks to look like strings while
keeping their extra information
"""
@staticmethod
def __new__(cls, text, lang, tkey):
"""
:param cls: the class to use when creating the instance
:param text: value for this key
:param lang: language code
:param tkey: UTF-8 version of the key name
"""
self = str.__new__(cls, text)
self.lang = lang
self.tkey = tkey
return self
class PngInfo(object):
"""
PNG chunk container (for use with save(pnginfo=))
"""
def __init__(self):
self.chunks = []
def add(self, cid, data):
"""Appends an arbitrary chunk. Use with caution.
:param cid: a byte string, 4 bytes long.
:param data: a byte string of the encoded data
"""
self.chunks.append((cid, data))
def add_itxt(self, key, value, lang="", tkey="", zip=False):
"""Appends an iTXt chunk.
:param key: latin-1 encodable text key name
:param value: value for this key
:param lang: language code
:param tkey: UTF-8 version of the key name
:param zip: compression flag
"""
if not isinstance(key, bytes):
key = key.encode("latin-1", "strict")
if not isinstance(value, bytes):
value = value.encode("utf-8", "strict")
if not isinstance(lang, bytes):
lang = lang.encode("utf-8", "strict")
if not isinstance(tkey, bytes):
tkey = tkey.encode("utf-8", "strict")
if zip:
self.add(b"iTXt", key + b"\0\x01\0" + lang + b"\0" + tkey + b"\0" +
zlib.compress(value))
else:
self.add(b"iTXt", key + b"\0\0\0" + lang + b"\0" + tkey + b"\0" +
value)
def add_text(self, key, value, zip=0):
"""Appends a text chunk.
:param key: latin-1 encodable text key name
:param value: value for this key, text or an
:py:class:`PIL.PngImagePlugin.iTXt` instance
:param zip: compression flag
"""
if isinstance(value, iTXt):
return self.add_itxt(key, value, value.lang, value.tkey, bool(zip))
# The tEXt chunk stores latin-1 text
if not isinstance(value, bytes):
try:
value = value.encode('latin-1', 'strict')
except UnicodeError:
return self.add_itxt(key, value, zip=bool(zip))
if not isinstance(key, bytes):
key = key.encode('latin-1', 'strict')
if zip:
self.add(b"zTXt", key + b"\0\0" + zlib.compress(value))
else:
self.add(b"tEXt", key + b"\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
self.text_memory = 0
def check_text_memory(self, chunklen):
self.text_memory += chunklen
if self.text_memory > MAX_TEXT_MEMORY:
raise ValueError("Too much memory used in text chunks: %s>MAX_TEXT_MEMORY" %
self.text_memory)
def chunk_iCCP(self, pos, length):
# ICC profile
s = ImageFile._safe_read(self.fp, length)
# 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 = s.find(b"\0")
logger.debug("iCCP profile name %r", s[:i])
logger.debug("Compression method %s", i8(s[i]))
comp_method = i8(s[i])
if comp_method != 0:
raise SyntaxError("Unknown compression method %s in iCCP chunk" %
comp_method)
try:
icc_profile = _safe_zlib_decompress(s[i+2:])
except ValueError:
if ImageFile.LOAD_TRUNCATED_IMAGES:
icc_profile = None
else:
raise
except zlib.error:
icc_profile = None # FIXME
self.im_info["icc_profile"] = icc_profile
return s
def chunk_IHDR(self, pos, length):
# image header
s = ImageFile._safe_read(self.fp, length)
self.im_size = i32(s), i32(s[4:])
try:
self.im_mode, self.im_rawmode = _MODES[(i8(s[8]), i8(s[9]))]
except:
pass
if i8(s[12]):
self.im_info["interlace"] = 1
if i8(s[11]):
raise SyntaxError("unknown filter category")
return s
def chunk_IDAT(self, pos, length):
# image data
self.im_tile = [("zip", (0, 0)+self.im_size, pos, self.im_rawmode)]
self.im_idat = length
raise EOFError
def chunk_IEND(self, pos, length):
# end of PNG image
raise EOFError
def chunk_PLTE(self, pos, length):
# palette
s = ImageFile._safe_read(self.fp, length)
if self.im_mode == "P":
self.im_palette = "RGB", s
return s
def chunk_tRNS(self, pos, length):
# transparency
s = ImageFile._safe_read(self.fp, length)
if self.im_mode == "P":
if _simple_palette.match(s):
# tRNS contains only one full-transparent entry,
# other entries are full opaque
i = s.find(b"\0")
if i >= 0:
self.im_info["transparency"] = i
else:
# otherwise, we have a byte string with one alpha value
# for each palette entry
self.im_info["transparency"] = s
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, length):
# gamma setting
s = ImageFile._safe_read(self.fp, length)
self.im_info["gamma"] = i32(s) / 100000.0
return s
def chunk_pHYs(self, pos, length):
# pixels per unit
s = ImageFile._safe_read(self.fp, length)
px, py = i32(s), i32(s[4:])
unit = i8(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, length):
# text
s = ImageFile._safe_read(self.fp, length)
try:
k, v = s.split(b"\0", 1)
except ValueError:
# fallback for broken tEXt tags
k = s
v = b""
if k:
if bytes is not str:
k = k.decode('latin-1', 'strict')
v = v.decode('latin-1', 'replace')
self.im_info[k] = self.im_text[k] = v
self.check_text_memory(len(v))
return s
def chunk_zTXt(self, pos, length):
# compressed text
s = ImageFile._safe_read(self.fp, length)
try:
k, v = s.split(b"\0", 1)
except ValueError:
k = s
v = b""
if v:
comp_method = i8(v[0])
else:
comp_method = 0
if comp_method != 0:
raise SyntaxError("Unknown compression method %s in zTXt chunk" %
comp_method)
try:
v = _safe_zlib_decompress(v[1:])
except ValueError:
if ImageFile.LOAD_TRUNCATED_IMAGES:
v = b""
else:
raise
except zlib.error:
v = b""
if k:
if bytes is not str:
k = k.decode('latin-1', 'strict')
v = v.decode('latin-1', 'replace')
self.im_info[k] = self.im_text[k] = v
self.check_text_memory(len(v))
return s
def chunk_iTXt(self, pos, length):
# international text
r = s = ImageFile._safe_read(self.fp, length)
try:
k, r = r.split(b"\0", 1)
except ValueError:
return s
if len(r) < 2:
return s
cf, cm, r = i8(r[0]), i8(r[1]), r[2:]
try:
lang, tk, v = r.split(b"\0", 2)
except ValueError:
return s
if cf != 0:
if cm == 0:
try:
v = _safe_zlib_decompress(v)
except ValueError:
if ImageFile.LOAD_TRUNCATED_IMAGES:
return s
else:
raise
except zlib.error:
return s
else:
return s
if bytes is not str:
try:
k = k.decode("latin-1", "strict")
lang = lang.decode("utf-8", "strict")
tk = tk.decode("utf-8", "strict")
v = v.decode("utf-8", "strict")
except UnicodeError:
return s
self.im_info[k] = self.im_text[k] = iTXt(v, lang, tk)
self.check_text_memory(len(v))
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 True:
#
# get next chunk
cid, pos, length = self.png.read()
try:
s = self.png.call(cid, pos, length)
except EOFError:
break
except AttributeError:
logger.debug("%r %s %s (unknown)", cid, pos, length)
s = ImageFile._safe_read(self.fp, length)
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 = length # 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, read_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, length = self.png.read()
if cid not in [b"IDAT", b"DDAT"]:
self.png.push(cid, pos, length)
return b""
self.__idat = length # empty chunks are allowed
# read more data from this chunk
if read_bytes <= 0:
read_bytes = self.__idat
else:
read_bytes = min(read_bytes, self.__idat)
self.__idat = self.__idat - read_bytes
return self.fp.read(read_bytes)
def load_end(self):
"internal: finished reading image data"
self.png.close()
self.png = None
# --------------------------------------------------------------------
# PNG writer
_OUTMODES = {
# supported PIL modes, and corresponding rawmodes/bits/color combinations
"1": ("1", b'\x01\x00'),
"L;1": ("L;1", b'\x01\x00'),
"L;2": ("L;2", b'\x02\x00'),
"L;4": ("L;4", b'\x04\x00'),
"L": ("L", b'\x08\x00'),
"LA": ("LA", b'\x08\x04'),
"I": ("I;16B", b'\x10\x00'),
"P;1": ("P;1", b'\x01\x03'),
"P;2": ("P;2", b'\x02\x03'),
"P;4": ("P;4", b'\x04\x03'),
"P": ("P", b'\x08\x03'),
"RGB": ("RGB", b'\x08\x02'),
"RGBA": ("RGBA", b'\x08\x06'),
}
def putchunk(fp, cid, *data):
"Write a PNG chunk (including CRC field)"
data = b"".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(object):
# 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, b"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 "bits" in im.encoderinfo:
# number of bits specified by user
colors = 1 << im.encoderinfo["bits"]
else:
# check palette contents
if im.palette:
colors = max(min(len(im.palette.getdata()[1])//3, 256), 2)
else:
colors = 256
if colors <= 2:
bits = 1
elif colors <= 4:
bits = 2
elif colors <= 16:
bits = 4
else:
bits = 8
if bits != 8:
mode = "%s;%d" % (mode, bits)
# encoder options
im.encoderconfig = (im.encoderinfo.get("optimize", False),
im.encoderinfo.get("compress_level", -1),
im.encoderinfo.get("compress_type", -1),
im.encoderinfo.get("dictionary", b""))
# 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, b"IHDR",
o32(im.size[0]), o32(im.size[1]), # 0: size
mode, # 8: depth/type
b'\0', # 10: compression
b'\0', # 11: filter category
b'\0') # 12: interlace flag
chunks = [b"cHRM", b"gAMA", b"sBIT", b"sRGB", b"tIME"]
icc = im.encoderinfo.get("icc_profile", im.info.get("icc_profile"))
if icc:
# 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)
name = b"ICC Profile"
data = name + b"\0\0" + zlib.compress(icc)
chunk(fp, b"iCCP", data)
else:
chunks.remove(b"sRGB")
info = im.encoderinfo.get("pnginfo")
if info:
chunks_multiple_allowed = [b"sPLT", b"iTXt", b"tEXt", b"zTXt"]
for cid, data in info.chunks:
if cid in chunks:
chunks.remove(cid)
chunk(fp, cid, data)
elif cid in chunks_multiple_allowed:
chunk(fp, cid, data)
if im.mode == "P":
palette_byte_number = (2 ** bits) * 3
palette_bytes = im.im.getpalette("RGB")[:palette_byte_number]
while len(palette_bytes) < palette_byte_number:
palette_bytes += b'\0'
chunk(fp, b"PLTE", palette_bytes)
transparency = im.encoderinfo.get('transparency',
im.info.get('transparency', None))
if transparency or transparency == 0:
if im.mode == "P":
# limit to actual palette size
alpha_bytes = 2**bits
if isinstance(transparency, bytes):
chunk(fp, b"tRNS", transparency[:alpha_bytes])
else:
transparency = max(0, min(255, transparency))
alpha = b'\xFF' * transparency + b'\0'
chunk(fp, b"tRNS", alpha[:alpha_bytes])
elif im.mode == "L":
transparency = max(0, min(65535, transparency))
chunk(fp, b"tRNS", o16(transparency))
elif im.mode == "RGB":
red, green, blue = transparency
chunk(fp, b"tRNS", o16(red) + o16(green) + o16(blue))
else:
if "transparency" in im.encoderinfo:
# don't bother with transparency if it's an RGBA
# and it's in the info dict. It's probably just stale.
raise IOError("cannot use transparency for this mode")
else:
if im.mode == "P" and im.im.getpalettemode() == "RGBA":
alpha = im.im.getpalette("RGBA", "A")
alpha_bytes = 2**bits
chunk(fp, b"tRNS", alpha[:alpha_bytes])
dpi = im.encoderinfo.get("dpi")
if dpi:
chunk(fp, b"pHYs",
o32(int(dpi[0] / 0.0254 + 0.5)),
o32(int(dpi[1] / 0.0254 + 0.5)),
b'\x01')
info = im.encoderinfo.get("pnginfo")
if info:
chunks = [b"bKGD", b"hIST"]
for cid, data in info.chunks:
if cid in chunks:
chunks.remove(cid)
chunk(fp, cid, data)
ImageFile._save(im, _idat(fp, chunk),
[("zip", (0, 0)+im.size, 0, rawmode)])
chunk(fp, b"IEND", b"")
if hasattr(fp, "flush"):
fp.flush()
# --------------------------------------------------------------------
# PNG chunk converter
def getchunks(im, **params):
"""Return a list of PNG chunks representing this image."""
class collector(object):
data = []
def write(self, data):
pass
def append(self, chunk):
self.data.append(chunk)
def append(fp, cid, *data):
data = b"".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(PngImageFile.format, PngImageFile, _accept)
Image.register_save(PngImageFile.format, _save)
Image.register_extension(PngImageFile.format, ".png")
Image.register_mime(PngImageFile.format, "image/png")
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