Preserve palette and transparency in zero dimension ImageOps results

Tests/test_imageops.py

@@ -106,6 +106,34 @@ def test_crop(
     assert_image_equal(ImageOps.crop(im, border), im.crop(expected_box))
 
 
+def test_zero() -> None:
+    def _check(
+        size: tuple[int, int],
+        operation: Callable[[Image.Image], Image.Image],
+        expected_size: tuple[int, int],
+    ) -> None:
+        im = Image.new("P", size)
+        im.putpalette(list(range(256)) * 3)
+        im.info["transparency"] = 0
+        new_im = operation(im)
+        assert new_im.getpalette(None) == im.getpalette(None)
+        assert new_im.info["transparency"] == 0
+        assert new_im.size == expected_size
+
+    _check((5, 5), lambda im: ImageOps.fit(im, (0, 5)), (0, 5))
+    _check((5, 0), lambda im: ImageOps.fit(im, (5, 5)), (5, 5))
+    _check((5, 5), lambda im: ImageOps.fit(im, (10, 0)), (10, 0))
+
+    _check((1, 10), lambda im: ImageOps.contain(im, (5, 5)), (0, 5))
+    _check((10, 1), lambda im: ImageOps.contain(im, (5, 5)), (5, 0))
+    _check((10, 0), lambda im: ImageOps.contain(im, (5, 5)), (5, 0))
+    _check((5, 5), lambda im: ImageOps.contain(im, (2, 0)), (0, 0))
+
+    _check((0, 10), lambda im: ImageOps.cover(im, (5, 5)), (0, 5))
+    _check((10, 0), lambda im: ImageOps.cover(im, (5, 5)), (5, 0))
+    _check((5, 5), lambda im: ImageOps.cover(im, (2, 0)), (0, 0))
+
+
 def test_1pxfit() -> None:
     # Division by zero in equalize if image is 1 pixel high
     newimg = ImageOps.fit(hopper("RGB").resize((1, 1)), (35, 35))
@@ -129,20 +157,6 @@ def test_fit_same_ratio() -> None:
         assert new_im.size == (1000, 755)
 
 
-def test_fit_zero() -> None:
-    im = Image.new("1", (5, 5))
-    new_im = ImageOps.fit(im, (0, 5))
-    assert new_im.width == 0
-
-    im = Image.new("1", (5, 0))
-    new_im = ImageOps.fit(im, (5, 5))
-    assert new_im.size == (5, 5)
-
-    im = Image.new("1", (5, 5))
-    new_im = ImageOps.fit(im, (10, 0))
-    assert new_im.size == (10, 0)
-
-
 @pytest.mark.parametrize("new_size", ((256, 256), (512, 256), (256, 512)))
 def test_contain(new_size: tuple[int, int]) -> None:
     im = hopper()
@@ -160,24 +174,6 @@ def test_contain_round() -> None:
     assert new_im.height == 5
 
 
-def test_contain_zero() -> None:
-    im = Image.new("1", (1, 10))
-    new_im = ImageOps.contain(im, (5, 5))
-    assert new_im.width == 0
-
-    im = Image.new("1", (10, 1))
-    new_im = ImageOps.contain(im, (5, 5))
-    assert new_im.height == 0
-
-    im = Image.new("1", (10, 0))
-    new_im = ImageOps.contain(im, (5, 5))
-    assert new_im.size == (5, 0)
-
-    im = Image.new("1", (5, 5))
-    new_im = ImageOps.contain(im, (2, 0))
-    assert new_im.size == (0, 0)
-
-
 @pytest.mark.parametrize(
     "image_name, expected_size",
     (
@@ -192,20 +188,6 @@ def test_cover(image_name: str, expected_size: tuple[int, int]) -> None:
         assert new_im.size == expected_size
 
 
-def test_cover_zero() -> None:
-    im = Image.new("1", (0, 10))
-    new_im = ImageOps.cover(im, (5, 5))
-    assert new_im.size == (0, 5)
-
-    im = Image.new("1", (10, 0))
-    new_im = ImageOps.cover(im, (5, 5))
-    assert new_im.size == (5, 0)
-
-    im = Image.new("1", (5, 5))
-    new_im = ImageOps.cover(im, (2, 0))
-    assert new_im.size == (0, 0)
-
-
 def test_pad() -> None:
     # Same ratio
     im = hopper()

src/PIL/Image.py

@@ -686,6 +686,7 @@ def _new(self, im: core.ImagingCore) -> Image:
         if im.mode in ("P", "PA"):
             if self.palette:
                 new.palette = self.palette.copy()
+                new.palette.dirty = 1
             else:
                 from . import ImagePalette
 

src/PIL/ImageOps.py

@@ -89,6 +89,10 @@ def _lut(image: Image.Image, lut: list[int], palette: bool = False) -> Image.Ima
         raise OSError(msg)
 
 
+def _new_empty(image: Image.Image, size: tuple[int, int]) -> Image.Image:
+    return image._new(Image.core.new(image.mode, size))
+
+
 #
 # actions
 
@@ -313,10 +317,10 @@ def contain(
     """
 
     if image.height == 0:
-        return Image.new(image.mode, (size[0], 0))
+        return _new_empty(image, (size[0], 0))
     im_ratio = image.width / image.height
     if size[1] == 0:
-        return Image.new(image.mode, (0, 0))
+        return _new_empty(image, (0, 0))
     dest_ratio = size[0] / size[1]
 
     if im_ratio != dest_ratio:
@@ -329,7 +333,7 @@ def contain(
             if new_width != size[0]:
                 size = (new_width, size[1])
     if min(size) == 0:
-        return Image.new(image.mode, size)
+        return _new_empty(image, size)
     return image.resize(size, resample=method)
 
 
@@ -350,12 +354,12 @@ def cover(
     """
 
     if image.width == 0:
-        return Image.new(image.mode, (0, size[1]))
+        return _new_empty(image, (0, size[1]))
     if image.height == 0:
-        return Image.new(image.mode, (size[0], 0))
+        return _new_empty(image, (size[0], 0))
     im_ratio = image.width / image.height
     if size[1] == 0:
-        return Image.new(image.mode, (0, 0))
+        return _new_empty(image, (0, 0))
     dest_ratio = size[0] / size[1]
 
     if im_ratio != dest_ratio:
@@ -606,7 +610,7 @@ def fit(
     # https://www.cazabon.com
 
     if min(size) == 0:
-        return Image.new(image.mode, size)
+        return _new_empty(image, size)
     centering_x, centering_y = centering
 
     if not 0.0 <= centering_x <= 1.0:
@@ -630,7 +634,7 @@ def fit(
 
     # calculate the aspect ratio of the live_size
     if live_size[1] == 0:
-        return Image.new(image.mode, size)
+        return _new_empty(image, size)
     live_size_ratio = live_size[0] / live_size[1]
 
     # calculate the aspect ratio of the output image