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improve simple palette detection for PNG

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- reverts change #1239 which could remove transparency from valid images
  (see test_save_p_transparent_black test case)
- improves simple palette detection to handle images from #1238
This commit is contained in:
Oliver Tonnhofer 2016-04-19 09:52:01 +02:00
parent 0f8d66bc96
commit c773688f37
1 changed files with 6 additions and 5 deletions
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11
PIL/PngImagePlugin.py
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@ -74,8 +74,7 @@ _MODES = {
} }
_simple_palette = re.compile(b'^\xff+\x00\xff*$') _simple_palette = re.compile(b'^\xff*\x00\xff*$')
_null_palette = re.compile(b'^\x00*$')
# Maximum decompressed size for a iTXt or zTXt chunk. # Maximum decompressed size for a iTXt or zTXt chunk.
# Eliminates decompression bombs where compressed chunks can expand 1000x # Eliminates decompression bombs where compressed chunks can expand 1000x
@ -118,7 +117,7 @@ class ChunkStream(object):
cid = s[4:] cid = s[4:]
pos = self.fp.tell() pos = self.fp.tell()
length = i32(s) length = i32(s)
if not is_cid(cid): if not is_cid(cid):
raise SyntaxError("broken PNG file (chunk %s)" % repr(cid)) raise SyntaxError("broken PNG file (chunk %s)" % repr(cid))
@ -359,12 +358,14 @@ class PngStream(ChunkStream):
s = ImageFile._safe_read(self.fp, length) s = ImageFile._safe_read(self.fp, length)
if self.im_mode == "P": if self.im_mode == "P":
if _simple_palette.match(s): if _simple_palette.match(s):
# tRNS contains only one full-transparent entry,
# other entries are full opaque
i = s.find(b"\0") i = s.find(b"\0")
if i >= 0: if i >= 0:
self.im_info["transparency"] = i self.im_info["transparency"] = i
elif _null_palette.match(s):
self.im_info["transparency"] = 0
else: else:
# otherwise, we have a byte string with one alpha value
# for each palette entry
self.im_info["transparency"] = s self.im_info["transparency"] = s
elif self.im_mode == "L": elif self.im_mode == "L":
self.im_info["transparency"] = i16(s) self.im_info["transparency"] = i16(s)