Keep ImageOps.contain dimensions at least one pixel

Tests/test_imageops.py

@@ -132,6 +132,20 @@ def test_contain(new_size: tuple[int, int]) -> None:
     assert new_im.size == (256, 256)
 
 
+@pytest.mark.parametrize("source_size", ((100, 1), (1, 100), (20, 1), (1, 20)))
+def test_contain_minimum_dimension(source_size: tuple[int, int]) -> None:
+    im = Image.new("RGB", source_size, "red")
+    result = ImageOps.contain(im, (10, 10))
+    expected_size = (10, 1) if source_size[0] > source_size[1] else (1, 10)
+    assert result.size == expected_size
+    assert result.getpixel((0, 0)) == (255, 0, 0)
+
+    padded = ImageOps.pad(im, (10, 10), color="blue")
+    assert padded.size == (10, 10)
+    assert padded.getpixel((4, 4)) == (255, 0, 0)
+    assert padded.getpixel((0, 0)) == (0, 0, 255)
+
+
 def test_contain_round() -> None:
     im = Image.new("1", (43, 63), 1)
     new_im = ImageOps.contain(im, (5, 7))

docs/releasenotes/13.0.0.rst

@@ -126,6 +126,14 @@ Two new filters are available for :py:meth:`~PIL.Image.Image.resize` and
 Other changes
 =============
 
+Keep resized dimensions positive in ImageOps.contain()
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+:py:func:`~PIL.ImageOps.contain` now keeps the calculated width or height at a
+minimum of one pixel. Previously, resizing a very narrow image could round one
+dimension to zero and raise ``ValueError``. This also fixes
+:py:func:`~PIL.ImageOps.pad` for these images.
+
 Python 3.15
 ^^^^^^^^^^^
 

src/PIL/ImageOps.py

@@ -300,11 +300,11 @@ def contain(
 
     if im_ratio != dest_ratio:
         if im_ratio > dest_ratio:
-            new_height = round(image.height / image.width * size[0])
+            new_height = max(1, round(image.height / image.width * size[0]))
             if new_height != size[1]:
                 size = (size[0], new_height)
         else:
-            new_width = round(image.width / image.height * size[1])
+            new_width = max(1, round(image.width / image.height * size[1]))
             if new_width != size[0]:
                 size = (new_width, size[1])
     return image.resize(size, resample=method)