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WIP: only convert GIF frames if palette actually changes #5974

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WIP: only convert GIF frames if palette actually changes #5974

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12 changes: 5 additions & 7 deletions Tests/test_file_gif.py
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Expand Up @@ -366,16 +366,12 @@ def test_dispose_background():
def test_dispose_background_transparency():
with Image.open("Tests/images/dispose_bgnd_transparency.gif") as img:
img.seek(2)
px = img.load()
px = img.convert("RGBA").load()
assert px[35, 30][3] == 0


def test_transparent_dispose():
expected_colors = [
(2, 1, 2),
((0, 255, 24, 255), (0, 0, 255, 255), (0, 255, 24, 255)),
((0, 0, 0, 0), (0, 0, 255, 255), (0, 0, 0, 0)),
]
expected_colors = [(2, 1, 2), (0, 1, 0), (2, 1, 2)]
with Image.open("Tests/images/transparent_dispose.gif") as img:
for frame in range(3):
img.seek(frame)
Expand Down Expand Up @@ -956,7 +952,9 @@ def test_missing_background():
# but the disposal method is "Restore to background color"
with Image.open("Tests/images/missing_background.gif") as im:
im.seek(1)
assert_image_equal_tofile(im, "Tests/images/missing_background_first_frame.png")
assert_image_equal_tofile(
im.convert("RGBA"), "Tests/images/missing_background_first_frame.png"
)


def test_saving_rgba(tmp_path):
Expand Down
92 changes: 64 additions & 28 deletions src/PIL/GifImagePlugin.py
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Expand Up @@ -55,6 +55,9 @@ class GifImageFile(ImageFile.ImageFile):

global_palette = None

constant_palette = True
last_palette = None

def data(self):
s = self.fp.read(1)
if s and s[0]:
Expand Down Expand Up @@ -82,7 +85,7 @@ def _open(self):
for i in range(0, len(p), 3):
if not (i // 3 == p[i] == p[i + 1] == p[i + 2]):
p = ImagePalette.raw("RGB", p)
self.global_palette = self.palette = p
self.global_palette = self.last_palette = self.palette = p
break

self.__fp = self.fp # FIXME: hack
Expand Down Expand Up @@ -164,25 +167,12 @@ def _seek(self, frame):
pass
self.__offset = 0

if self.__frame == 1:
self.pyaccess = None
if "transparency" in self.info:
self.mode = "RGBA"
self.im.putpalettealpha(self.info["transparency"], 0)
self.im = self.im.convert("RGBA", Image.FLOYDSTEINBERG)

del self.info["transparency"]
else:
self.mode = "RGB"
self.im = self.im.convert("RGB", Image.FLOYDSTEINBERG)
if self.dispose:
self.im.paste(self.dispose, self.dispose_extent)

palette = None

info = {}
frame_transparency = None
interlace = None
tmp_dispose_extent = None
while True:

s = self.fp.read(1)
Expand Down Expand Up @@ -247,7 +237,7 @@ def _seek(self, frame):
x1, y1 = x0 + i16(s, 4), y0 + i16(s, 6)
if x1 > self.size[0] or y1 > self.size[1]:
self._size = max(x1, self.size[0]), max(y1, self.size[1])
self.dispose_extent = x0, y0, x1, y1
tmp_dispose_extent = x0, y0, x1, y1
flags = s[8]

interlace = (flags & 64) != 0
Expand All @@ -267,6 +257,41 @@ def _seek(self, frame):

frame_palette = palette or self.global_palette

# as long as we have a constant palette, we check whether this frame
# still has the same palette
if self.constant_palette:
if self.last_palette is None:
self.last_palette = palette
else:
if self.last_palette != frame_palette:
self.constant_palette = False

if self.__frame > 0:
# for every frame after the first frame, we check whether the
# palette is still constant and convert to RGB or RGBA if not
self.pyaccess = None
if not self.constant_palette and self.mode not in ("RGB", "RGBA"):
if "transparency" in self.info:
self.mode = "RGBA"
self.im.putpalettealpha(self.info["transparency"], 0)
self.im = self.im.convert("RGBA", Image.FLOYDSTEINBERG)
if self.dispose:
self.dispose = self.dispose.convert(
"RGBA", Image.FLOYDSTEINBERG
)

del self.info["transparency"]
else:
self.mode = "RGB"
self.im = self.im.convert("RGB", Image.FLOYDSTEINBERG)
if self.dispose:
self.dispose = self.dispose.convert("RGB", Image.FLOYDSTEINBERG)
if self.dispose:
self.im.paste(self.dispose, self.dispose_extent)

if tmp_dispose_extent is not None:
self.dispose_extent = tmp_dispose_extent

def _rgb(color):
if frame_palette:
color = tuple(frame_palette.palette[color * 3 : color * 3 + 3])
Expand All @@ -289,13 +314,18 @@ def _rgb(color):

# by convention, attempt to use transparency first
color = self.info.get("transparency", frame_transparency)
if color is not None:
dispose_mode = "RGBA"
color = _rgb(color) + (0,)
if self.constant_palette:
if color is None:
color = self.info.get("background", 0)
self.dispose = Image.core.fill("P", dispose_size, color)
else:
dispose_mode = "RGB"
color = _rgb(self.info.get("background", 0))
self.dispose = Image.core.fill(dispose_mode, dispose_size, color)
if color is not None:
dispose_mode = "RGBA"
color = _rgb(color) + (0,)
else:
dispose_mode = "RGB"
color = _rgb(self.info.get("background", 0))
self.dispose = Image.core.fill(dispose_mode, dispose_size, color)
else:
# replace with previous contents
if self.im:
Expand All @@ -307,7 +337,11 @@ def _rgb(color):

Image._decompression_bomb_check(dispose_size)
self.dispose = Image.core.fill(
"RGBA", dispose_size, _rgb(frame_transparency) + (0,)
"P" if self.constant_palette else "RGBA",
dispose_size,
frame_transparency
if self.constant_palette
else _rgb(frame_transparency) + (0,),
)
except AttributeError:
pass
Expand Down Expand Up @@ -367,11 +401,13 @@ def load_prepare(self):
def load_end(self):
if self.__frame == 0:
return
if self._frame_transparency is not None:
self.im.putpalettealpha(self._frame_transparency, 0)
frame_im = self.im.convert("RGBA")
else:
frame_im = self.im.convert("RGB")
frame_im = self.im
if self._prev_im.mode != self.im.mode:
if self._frame_transparency is not None:
self.im.putpalettealpha(self._frame_transparency, 0)
frame_im = self.im.convert("RGBA")
else:
frame_im = self.im.convert("RGB")
frame_im = self._crop(frame_im, self.dispose_extent)

self.im = self._prev_im
Expand Down