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Correct byte order when resampling I;16B and I;16N images #10286

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Merged
radarhere merged 2 commits into from
Oct 23, 2026
+18 −4
Merged

Correct byte order when resampling I;16B and I;16N images #10286

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8323bec
Correct byte order when resampling I;16B and I;16N images
mkantautas Oct 22, 2026
1700e28
Simplify test
radarhere Oct 23, 2026
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7 changes: 7 additions & 0 deletions Tests/test_image_resize.py
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,13 @@ def test_endianness(
# as separately resized channel
assert_image_equal(ch, references[channels[i]])

@pytest.mark.parametrize("mode", ("I;16", "I;16L", "I;16B", "I;16N"))
def test_i16(self, mode: str) -> None:
im = Image.new(mode, (1, 2))
im.putdata((0x0099, 0x0100))
resized = self.resize(im, (1, 1), Image.Resampling.BICUBIC)
assert resized.getpixel((0, 0)) == 0x00CD

@pytest.mark.parametrize(
"resample",
(
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7 changes: 7 additions & 0 deletions docs/releasenotes/13.1.0.rst
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Expand Up @@ -49,6 +49,13 @@ TODO
Other changes
=============

Resizing I;16B and I;16N images
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

On little-endian systems, :py:meth:`~PIL.Image.Image.resize` read and wrote
I;16B and I;16N pixel values in the wrong byte order when using a resampling
filter other than ``Resampling.NEAREST``. This has been fixed.

Blurring I;16 images
^^^^^^^^^^^^^^^^^^^^

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8 changes: 4 additions & 4 deletions src/libImaging/Resample.c
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Expand Up @@ -551,9 +551,9 @@ _ImagingResampleHorizontal_16bpc(

int bigendian = 0;
if (
imIn->mode == IMAGING_MODE_I_16N
imIn->mode == IMAGING_MODE_I_16B
#ifdef WORDS_BIGENDIAN
|| imIn->mode == IMAGING_MODE_I_16B
|| imIn->mode == IMAGING_MODE_I_16N
#endif
) {
bigendian = 1;
Expand Down Expand Up @@ -602,9 +602,9 @@ _ImagingResampleVertical_16bpc(

int bigendian = 0;
if (
imIn->mode == IMAGING_MODE_I_16N
imIn->mode == IMAGING_MODE_I_16B
#ifdef WORDS_BIGENDIAN
|| imIn->mode == IMAGING_MODE_I_16B
|| imIn->mode == IMAGING_MODE_I_16N
#endif
) {
bigendian = 1;
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