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Improved ImagePalette #5552

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hugovk merged 16 commits into from
Jun 28, 2021
Merged

Improved ImagePalette #5552

hugovk merged 16 commits into from
Jun 28, 2021

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@radarhere
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@radarhere radarhere commented Jun 23, 2021 •
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This PR has several changes

  • the ImagePalette colors dictionary is currently empty when the object is created, rather than being filled with palette entries. This fixes that
  • it changes the palette to be empty by default. This means that new colors can be appended more easily, rather than finding that all 256 entries are already occupied
  • if a new color is added when 256 entries are taken, search through the image. If there is a palette index that isn't actually used, use that for the new color
  • helps ImageOps.expand distorts image and converts png to grayscale #5375 by determining the border palette index on the new image only after the palette has been attached

Edit: Thanks to later commits, resolves #2803

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radarhere commented Jun 27, 2021 •
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I've pushed another commit to not use ImagePalette.raw in convert. Since this code -

Pillow/src/PIL/Image.py

Lines 1012 to 1019 in 52856bc

new.palette = ImagePalette.raw("RGB", new.im.getpalette("RGB"))
if delete_trns:
# This could possibly happen if we requantize to fewer colors.
# The transparency would be totally off in that case.
del new.info["transparency"]
if trns is not None:
try:
new.info["transparency"] = new.palette.getcolor(trns)

is currently always going to raise a ValueError.

Pillow/src/PIL/ImagePalette.py

Lines 142 to 144 in 52856bc

def raw(rawmode, data):
palette = ImagePalette()
palette.rawmode = rawmode

Pillow/src/PIL/ImagePalette.py

Lines 90 to 96 in 52856bc

def getcolor(self, color):
"""Given an rgb tuple, allocate palette entry.
.. warning:: This method is experimental.
"""
if self.rawmode:
raise ValueError("palette contains raw palette data")

This fixes the UserWarning in #2803

radarhere
radarhere commented Jun 27, 2021
View reviewed changes
Tests/test_file_apng.py
assert im.getpixel((0, 0)) == (0, 255, 0, 255)
assert im.getpixel((64, 32)) == (0, 255, 0, 255)
assert im.getpixel((0, 0)) == (255, 0, 0, 0)
assert im.getpixel((64, 32)) == (255, 0, 0, 0)
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Using https://pypi.org/project/apng/ to split Tests/images/apng/mode_palette_alpha.png into frames, this matches the transparent third frame

radarhere
radarhere commented Jun 27, 2021
View reviewed changes
Tests/test_imageops.py
im_cropped = im_expanded.crop(
(10, 10, im_expanded.width - 10, im_expanded.height - 10)
)
assert_image_equal(im_cropped, im)
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Expanding the test from #5551, bringing it closer to #5375

@radarhere radarhere mentioned this pull request Jun 28, 2021
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radarhere commented Jun 28, 2021 •
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I've now pushed a commit, 'Fixed reloading palette'. It allows this code to work.

from PIL import Image
im = Image.open("Tests/images/hopper.gif")
im.load()
im.palette.dirty = 1
im.save("out.png")

In master at the moment, it produces this broken output.
out

And with the addition of that change, this PR now resolves #2803

@hugovk hugovk merged commit 5030223 into python-pillow:master Jun 28, 2021
@radarhere radarhere deleted the palette branch June 28, 2021 22:57
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@radarhere radarhere mentioned this pull request Sep 25, 2023
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Exception when converting GIF to RGB and saving

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