Enrich tests for putpalette function

[moghadas76]

putpalette methods in masked images raises ValueError. It should be fixed

[moghadas76]

In tests, I've put the tested image : Tests/images/FudanPed00003_mask.png

[moghadas76]

By matplotlib you can view the image correctly:

import matplotlib.pyplot as plt

mask = Image.open('/content/PennFudanPed/PedMasks/FudanPed00001_mask.png')
# # each mask instance has a different color, from zero to N, where
# # N is the number of instances. In order to make visualization easier,
# # let's adda color palette to the mask.
fig, axes = plt.subplots(1, 3, figsize=(16, 12))
ax = axes.flatten()

ax[0].imshow(mask, cmap="gray")
ax[0].set_axis_off()
ax[0].set_title("Mask", fontsize=12)

ax[1].imshow(mask, cmap="gray")
ax[1].set_axis_off()
ax[1].set_title("Mask", fontsize=12)

ax[2].imshow(mask, cmap="gray")
ax[2].set_axis_off()
ax[2].set_title("Masked", fontsize=12)

plt.show()

[radarhere]

If you are interested in a workaround, you can just load() the image first.

mask = Image.open(valid_file)
mask.load()
mask.putpalette(
    [
        0,
        0,
        0,  # black background
        255,
        0,
        0,  # index 1 is red
        255,
        255,
        0,  # index 2 is yellow
        255,
        153,
        0,  # index 3 is orange
    ]
)

[moghadas76]

So this is a code smell. Could I fix this?

[moghadas76]

Internally it is called load!

def putpalette(self, data, rawmode="RGB"):
        """
        Attaches a palette to this image.  The image must be a "P", "PA", "L"
        or "LA" image.

        The palette sequence must contain at most 256 colors, made up of one
        integer value for each channel in the raw mode.
        For example, if the raw mode is "RGB", then it can contain at most 768
        values, made up of red, green and blue values for the corresponding pixel
        index in the 256 colors.
        If the raw mode is "RGBA", then it can contain at most 1024 values,
        containing red, green, blue and alpha values.

        Alternatively, an 8-bit string may be used instead of an integer sequence.

        :param data: A palette sequence (either a list or a string).
        :param rawmode: The raw mode of the palette. Either "RGB", "RGBA", or a mode
           that can be transformed to "RGB" or "RGBA" (e.g. "R", "BGR;15", "RGBA;L").
        """
        from . import ImagePalette

        if self.mode not in ("L", "LA", "P", "PA"):
            msg = "illegal image mode"
            raise ValueError(msg)
        if isinstance(data, ImagePalette.ImagePalette):
            palette = ImagePalette.raw(data.rawmode, data.palette)
        else:
            if not isinstance(data, bytes):
                data = bytes(data)
            palette = ImagePalette.raw(rawmode, data)
        self.mode = "PA" if "A" in self.mode else "P"
        self.palette = palette
        self.palette.mode = "RGB"
        self.load()  # install new palette

[radarhere]

Yes, load() is called internally, but after the mode is changed. The problem is that your grayscale image, L mode, is being loaded directly in as an image with a palette, P mode, which our mechanism for unpacking image data doesn't support at the moment.

I've created PR #7187 to fix this and add a test for it.

[moghadas76]

Great. So could you merge this PR?

[radarhere]

You'd like this PR merged?

Your test runs your scenario, and then asserts that it failed. This is the opposite of what we typically do, where we assert correct behaviour. If one of our tests fails, that generally indicates that something is broken and action needs to be taken to fix it. If your test were to fail, the only action to take is to remove your test.

We do have some tests that are known to fail, using xfail - see https://docs.pytest.org/en/7.3.x/how-to/skipping.html#xfail-mark-test-functions-as-expected-to-fail - but those are scenarios where we don't have a viable fix.

My PR does have a fix, and indeed, if my PR is merged, then the test in this PR would start to fail.

[radarhere]

To demonstrate that this would start failing if my PR is merged, I checked out your branch and cherry-picked the commit from my PR onto it. You can see the result here - https://github.com/radarhere/Pillow/actions/runs/5090886719/jobs/9150255542

[moghadas76]

Fine. Merge your branch, after that I'll fix my test

[radarhere]

#7187 has been merged.