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Use disposal settings from previous frame in APNG #5126

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merged 1 commit into from Dec 31, 2020
Merged

Use disposal settings from previous frame in APNG #5126

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Binary file added Tests/images/apng/dispose_op_previous_frame.png
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25 changes: 25 additions & 0 deletions Tests/test_file_apng.py
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Expand Up @@ -105,6 +105,31 @@ def test_apng_dispose_region():
assert im.getpixel((64, 32)) == (0, 255, 0, 255)


def test_apng_dispose_op_previous_frame():
# Test that the dispose settings being used are from the previous frame
#
# Image created with:
# red = Image.new("RGBA", (128, 64), (255, 0, 0, 255))
# green = red.copy()
# green.paste(Image.new("RGBA", (64, 32), (0, 255, 0, 255)))
# blue = red.copy()
# blue.paste(Image.new("RGBA", (64, 32), (0, 255, 0, 255)), (64, 32))
#
# red.save(
# "Tests/images/apng/dispose_op_previous_frame.png",
# save_all=True,
# append_images=[green, blue],
# disposal=[
# PngImagePlugin.APNG_DISPOSE_OP_NONE,
# PngImagePlugin.APNG_DISPOSE_OP_PREVIOUS,
# PngImagePlugin.APNG_DISPOSE_OP_PREVIOUS
# ],
# )
with Image.open("Tests/images/apng/dispose_op_previous_frame.png") as im:
im.seek(im.n_frames - 1)
assert im.getpixel((0, 0)) == (255, 0, 0, 255)


def test_apng_dispose_op_background_p_mode():
with Image.open("Tests/images/apng/dispose_op_background_p_mode.png") as im:
im.seek(1)
Expand Down
117 changes: 58 additions & 59 deletions src/PIL/PngImagePlugin.py
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Expand Up @@ -803,60 +803,76 @@ def _seek(self, frame, rewind=False):
self.blend_op = self.info.get("blend")
self.dispose_extent = self.info.get("bbox")
self.__frame = 0
return
else:
if frame != self.__frame + 1:
raise ValueError(f"cannot seek to frame {frame}")

# ensure previous frame was loaded
self.load()
# ensure previous frame was loaded
self.load()

self.fp = self.__fp
if self.dispose:
self.im.paste(self.dispose, self.dispose_extent)
self._prev_im = self.im.copy()

# advance to the next frame
if self.__prepare_idat:
ImageFile._safe_read(self.fp, self.__prepare_idat)
self.__prepare_idat = 0
frame_start = False
while True:
self.fp.read(4) # CRC
self.fp = self.__fp

try:
cid, pos, length = self.png.read()
except (struct.error, SyntaxError):
break
# advance to the next frame
if self.__prepare_idat:
ImageFile._safe_read(self.fp, self.__prepare_idat)
self.__prepare_idat = 0
frame_start = False
while True:
self.fp.read(4) # CRC

if cid == b"IEND":
raise EOFError("No more images in APNG file")
if cid == b"fcTL":
if frame_start:
# there must be at least one fdAT chunk between fcTL chunks
raise SyntaxError("APNG missing frame data")
frame_start = True
try:
cid, pos, length = self.png.read()
except (struct.error, SyntaxError):
break

try:
self.png.call(cid, pos, length)
except UnicodeDecodeError:
break
except EOFError:
if cid == b"fdAT":
length -= 4
if cid == b"IEND":
raise EOFError("No more images in APNG file")
if cid == b"fcTL":
if frame_start:
self.__prepare_idat = length
break
ImageFile._safe_read(self.fp, length)
except AttributeError:
logger.debug("%r %s %s (unknown)", cid, pos, length)
ImageFile._safe_read(self.fp, length)
# there must be at least one fdAT chunk between fcTL chunks
raise SyntaxError("APNG missing frame data")
frame_start = True

self.__frame = frame
self.tile = self.png.im_tile
self.dispose_op = self.info.get("disposal")
self.blend_op = self.info.get("blend")
self.dispose_extent = self.info.get("bbox")
try:
self.png.call(cid, pos, length)
except UnicodeDecodeError:
break
except EOFError:
if cid == b"fdAT":
length -= 4
if frame_start:
self.__prepare_idat = length
break
ImageFile._safe_read(self.fp, length)
except AttributeError:
logger.debug("%r %s %s (unknown)", cid, pos, length)
ImageFile._safe_read(self.fp, length)

self.__frame = frame
self.tile = self.png.im_tile
self.dispose_op = self.info.get("disposal")
self.blend_op = self.info.get("blend")
self.dispose_extent = self.info.get("bbox")

if not self.tile:
raise EOFError

# setup frame disposal (actual disposal done when needed in the next _seek())
if self._prev_im is None and self.dispose_op == APNG_DISPOSE_OP_PREVIOUS:
self.dispose_op = APNG_DISPOSE_OP_BACKGROUND

if not self.tile:
raise EOFError
if self.dispose_op == APNG_DISPOSE_OP_PREVIOUS:
self.dispose = self._prev_im.copy()
self.dispose = self._crop(self.dispose, self.dispose_extent)
elif self.dispose_op == APNG_DISPOSE_OP_BACKGROUND:
self.dispose = Image.core.fill(self.mode, self.size)
self.dispose = self._crop(self.dispose, self.dispose_extent)
else:
self.dispose = None

def tell(self):
return self.__frame
Expand Down Expand Up @@ -939,19 +955,6 @@ def load_end(self):
self.png.close()
self.png = None
else:
# setup frame disposal (actual disposal done when needed in _seek())
if self._prev_im is None and self.dispose_op == APNG_DISPOSE_OP_PREVIOUS:
self.dispose_op = APNG_DISPOSE_OP_BACKGROUND

if self.dispose_op == APNG_DISPOSE_OP_PREVIOUS:
dispose = self._prev_im.copy()
dispose = self._crop(dispose, self.dispose_extent)
elif self.dispose_op == APNG_DISPOSE_OP_BACKGROUND:
dispose = Image.core.fill(self.im.mode, self.size)
dispose = self._crop(dispose, self.dispose_extent)
else:
dispose = None

if self._prev_im and self.blend_op == APNG_BLEND_OP_OVER:
updated = self._crop(self.im, self.dispose_extent)
self._prev_im.paste(
Expand All @@ -960,10 +963,6 @@ def load_end(self):
self.im = self._prev_im
if self.pyaccess:
self.pyaccess = None
self._prev_im = self.im.copy()

if dispose:
self._prev_im.paste(dispose, self.dispose_extent)

def _getexif(self):
if "exif" not in self.info:
Expand Down