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Handle transparency between frames for animated GIFs

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Show the previous frame for transparent pixels when the disposal method is 'do not dispose'.

This fixes issue 634.
This commit is contained in:
Lars Jørgen Solberg 2014-07-03 18:48:12 +02:00
parent 08a9bdbcd6
commit f88a355c6c
1 changed files with 18 additions and 5 deletions
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23
PIL/GifImagePlugin.py
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@ -99,6 +99,8 @@ class GifImageFile(ImageFile.ImageFile):
self.dispose_extent = [0, 0, 0, 0] #x0, y0, x1, y1 self.dispose_extent = [0, 0, 0, 0] #x0, y0, x1, y1
self.__frame = -1 self.__frame = -1
self.__fp.seek(self.__rewind) self.__fp.seek(self.__rewind)
self._prev_im = None
self.disposal_method = 0
if frame != self.__frame + 1: if frame != self.__frame + 1:
raise ValueError("cannot seek to frame %d" % frame) raise ValueError("cannot seek to frame %d" % frame)
@ -120,7 +122,6 @@ class GifImageFile(ImageFile.ImageFile):
from copy import copy from copy import copy
self.palette = copy(self.global_palette) self.palette = copy(self.global_palette)
disposal_method = 0
while True: while True:
s = self.fp.read(1) s = self.fp.read(1)
@ -143,8 +144,8 @@ class GifImageFile(ImageFile.ImageFile):
self.info["duration"] = i16(block[1:3]) * 10 self.info["duration"] = i16(block[1:3]) * 10
# disposal method - find the value of bits 4 - 6 # disposal method - find the value of bits 4 - 6
disposal_method = 0b00011100 & flags self.disposal_method = 0b00011100 & flags
disposal_method = disposal_method >> 2 self.disposal_method = self.disposal_method >> 2
elif i8(s) == 255: elif i8(s) == 255:
# #
# application extension # application extension
@ -190,10 +191,10 @@ class GifImageFile(ImageFile.ImageFile):
# raise IOError, "illegal GIF tag `%x`" % i8(s) # raise IOError, "illegal GIF tag `%x`" % i8(s)
try: try:
if disposal_method < 2: if self.disposal_method < 2:
# do not dispose or none specified # do not dispose or none specified
self.dispose = None self.dispose = None
elif disposal_method == 2: elif self.disposal_method == 2:
# replace with background colour # replace with background colour
self.dispose = Image.core.fill("P", self.size, self.dispose = Image.core.fill("P", self.size,
self.info["background"]) self.info["background"])
@ -220,6 +221,18 @@ class GifImageFile(ImageFile.ImageFile):
def tell(self): def tell(self):
return self.__frame return self.__frame
def load_end(self):
ImageFile.ImageFile.load_end(self)
# if the disposal method is 'do not dispose', transparent
# pixels should show the content of the previous frame
if self._prev_im and self.disposal_method == 1:
# we do this by pasting the updated area onto the previous
# frame which we then use as the current image content
updated = self.im.crop(self.dispose_extent)
self._prev_im.paste(updated, self.dispose_extent, updated.convert('RGBA'))
self.im = self._prev_im
self._prev_im = self.im.copy()
# -------------------------------------------------------------------- # --------------------------------------------------------------------
# Write GIF files # Write GIF files