test_file_blp.py fails with libjpeg 9e since 9.3.0

[kulikjak]

What did you do?

I built Pillow 9.3.0 as downloaded from PyPI and ran the test suite with the following command:
/usr/bin/python3.X -m pytest Tests/test_file_blp.py

What did you expect to happen?

Every test passes.

What actually happened?

test_load_blp1 failed with the following error:

    def test_load_blp1():
        with Image.open("Tests/images/blp/blp1_jpeg.blp") as im:
>           assert_image_equal_tofile(im, "Tests/images/blp/blp1_jpeg.png")

Tests/test_file_blp.py:15: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
Tests/helper.py:105: in assert_image_equal_tofile
    assert_image_equal(a, img, msg)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

a = <PIL.BlpImagePlugin.BlpImageFile image mode=RGB size=256x256 at 0x7FF952EF3AD10>
b = <PIL.PngImagePlugin.PngImageFile image mode=RGB size=256x256 at 0x7FF952EF3AF10>, msg = None

    def assert_image_equal(a, b, msg=None):
        assert a.mode == b.mode, msg or f"got mode {repr(a.mode)}, expected {repr(b.mode)}"
        assert a.size == b.size, msg or f"got size {repr(a.size)}, expected {repr(b.size)}"
        if a.tobytes() != b.tobytes():
            if HAS_UPLOADER:
                try:
                    url = test_image_results.upload(a, b)
                    logger.error(f"Url for test images: {url}")
                except Exception:
                    pass
    
>           assert False, msg or "got different content"
E           AssertionError: got different content
E           assert False

I don't see this failure in 9.2.0 - it seems that f7363c1 caused this issue. When I revert it, the issue is gone (when I revert only the BlpImagePlugin.py change, pillow segfaults on newly added test_file_blp.py code, but it passes the assert_image_equal_tofile part this failure is about.

This happens on both SPARC and Intel meaning than endianness is most likely not the issue.

What are your OS, Python and Pillow versions?

• OS: Oracle Solaris 11.4 (both on SPARC and x86)
• Python: 3.7.14, 3.9.14 and 3.11.0
• Pillow: 9.3.0

[radarhere]

Hi. Just to help us reproduce this, what version of libjpeg are you using? python3.X -m PIL | grep "JPEG support"

[kulikjak]

JPEG support ok, compiled for 9.0 - specifically it's 9e.

I will try running it with a different libjpeg and see if that helps things.

[radarhere]

No need to do that.

JPEG images are allowed to be loaded slightly differently. So presuming that the difference is not too great, the test just needs to be relaxed to allow for variation.

If you change test_file_blp.py, replacing

assert_image_equal_tofile(im, "Tests/images/blp/blp1_jpeg.png")

with

with Image.open("Tests/images/blp/blp1_jpeg.png") as expected:
    assert_image_similar(im, expected., 0.001)

the error should change to report an average pixel difference. What is that number?

[kulikjak]

I am getting the following:

E           AssertionError:  average pixel value difference 537.3142 > epsilon 0.0010
E           assert 0.001 >= 537.3141937255859

Doesn't seem like a small difference :(.

[kulikjak]

I just tested it on older machine where we still have libjpeg v6b2 and I see no issue there.

[radarhere]

Testing, I find that 9d is fine, but 9e is not. Interesting. The problem is not Solaris at least.

These are the images with 9d and 9e.

9d	9e

Here is the extracted JPEG

And here is what it is resaved by Pillow. So this is essentially a JPEG problem.

9d	9e

[radarhere]

The reason that this wasn't detected sooner is that Pillow tests with libjpeg-turbo.

[kulikjak]

Thanks for the investigation! I renamed the issue to reflect that it's not Solaris but the latest libjpeg that causes this.

Interesting that when I revert f7363c1, it works with 9e as well. But I guess that that might be just a coincidence.

So, should this issue be reported to libjpeg maintainers instead?

[radarhere]

Do you know where to do that? https://sourceforge.net/p/libjpeg/bugs/ hardly seems active.

[radarhere]

I've created a reproduction not using Pillow, but jpeglib - /~https://github.com/radarhere/Pillow/tree/6741. This is a library that allow easy switching between libjpeg versions.

import jpeglib
jpeglib.version.set('9d')
im = jpeglib.read_spatial("extracted.jpg")
print("9d", im.spatial[0, 0])
jpeglib.version.set('9e')
im = jpeglib.read_spatial("extracted.jpg")
print("9e", im.spatial[0, 0])

gives

9d [  1  50   1 255]
9e [255 136 255 255]

[radarhere]

I've submitted an enquiry using the contact form at https://jpegclub.org/reference/contact/

[kulikjak]

Thanks - I also don't know what the correct way to report issues is - https://sourceforge.net/p/libjpeg/bugs/ seems to have one bug filed not that long ago (and with a reaction), but the contact form might also be a good idea.