Fix putdata() for I;16N on big-endian

Tests/helper.py

@@ -261,7 +261,11 @@ def hopper(mode: str | None = None, cache: dict[str, Image.Image] = {}) -> Image
     # (for fast, isolated, repeatable tests).
     im = cache.get(mode)
     if im is None:
-        if mode == "F":
+        if mode == "RGBa":
+            im = hopper("RGBA").convert(mode)
+        elif mode == "La":
+            im = hopper("LA").convert(mode)
+        elif mode == "F":
             im = hopper("L").convert(mode)
         elif mode[:4] == "I;16":
             im = hopper("I").convert(mode)

Tests/test_image.py

@@ -33,36 +33,38 @@
     skip_unless_feature,
 )
 
+# name, number of bands, pixel size
+image_modes = (
+    ("1", 1, 1),
+    ("L", 1, 1),
+    ("LA", 2, 4),
+    ("La", 2, 4),
+    ("P", 1, 1),
+    ("PA", 2, 4),
+    ("F", 1, 4),
+    ("I", 1, 4),
+    ("I;16", 1, 2),
+    ("I;16L", 1, 2),
+    ("I;16B", 1, 2),
+    ("I;16N", 1, 2),
+    ("RGB", 3, 4),
+    ("RGBA", 4, 4),
+    ("RGBa", 4, 4),
+    ("RGBX", 4, 4),
+    ("BGR;15", 3, 2),
+    ("BGR;16", 3, 2),
+    ("BGR;24", 3, 3),
+    ("CMYK", 4, 4),
+    ("YCbCr", 3, 4),
+    ("HSV", 3, 4),
+    ("LAB", 3, 4),
+)
+
+image_mode_names = [name for name, num_bands, pixelsize in image_modes]
+
 
 class TestImage:
-    @pytest.mark.parametrize(
-        "mode",
-        (
-            "1",
-            "P",
-            "PA",
-            "L",
-            "LA",
-            "La",
-            "F",
-            "I",
-            "I;16",
-            "I;16L",
-            "I;16B",
-            "I;16N",
-            "RGB",
-            "RGBX",
-            "RGBA",
-            "RGBa",
-            "BGR;15",
-            "BGR;16",
-            "BGR;24",
-            "CMYK",
-            "YCbCr",
-            "LAB",
-            "HSV",
-        ),
-    )
+    @pytest.mark.parametrize("mode", image_mode_names)
     def test_image_modes_success(self, mode: str) -> None:
         Image.new(mode, (1, 1))
 
@@ -1042,6 +1044,53 @@ def test_close_graceful(self, caplog: pytest.LogCaptureFixture) -> None:
             assert im.fp is None
 
 
+class TestImageBytes:
+    sample_bytes = bytes(
+        range(2 * 2 * max(pixelsize for mode, num_bands, pixelsize in image_modes))
+    )
+
+    @pytest.mark.parametrize("mode", image_mode_names)
+    def test_roundtrip_bytes_constructor(self, mode: str):
+        source_image = hopper(mode)
+        source_bytes = source_image.tobytes()
+        copy_image = Image.frombytes(mode, source_image.size, source_bytes)
+        assert copy_image.tobytes() == source_bytes
+
+    @pytest.mark.parametrize("mode", image_mode_names)
+    def test_roundtrip_bytes_method(self, mode: str):
+        source_image = hopper(mode)
+        source_bytes = source_image.tobytes()
+        copy_image = Image.new(mode, source_image.size)
+        copy_image.frombytes(source_bytes)
+        assert copy_image.tobytes() == source_bytes
+
+    @pytest.mark.parametrize(("mode", "num_bands", "pixelsize"), image_modes)
+    def test_pixels_after_getdata_putdata(
+        self, mode: str, num_bands: int, pixelsize: int
+    ):
+        image_byte_size = 2 * 2 * pixelsize
+        start_bytes = self.sample_bytes[:image_byte_size]
+        image = Image.frombytes(mode, (2, 2), start_bytes)
+
+        start_pixels = (
+            image.getpixel((0, 0)),
+            image.getpixel((0, 1)),
+            image.getpixel((1, 0)),
+            image.getpixel((1, 1)),
+        )
+
+        image.putdata(image.getdata())
+
+        end_pixels = (
+            image.getpixel((0, 0)),
+            image.getpixel((0, 1)),
+            image.getpixel((1, 0)),
+            image.getpixel((1, 1)),
+        )
+
+        assert start_pixels == end_pixels
+
+
 class MockEncoder(ImageFile.PyEncoder):
     pass
 

src/_imaging.c

@@ -1578,7 +1578,17 @@ if (PySequence_Check(op)) { \
                 int bigendian = 0;
                 if (image->type == IMAGING_TYPE_SPECIAL) {
                     // I;16*
-                    bigendian = strcmp(image->mode, "I;16B") == 0;
+                    if (strcmp(image->mode, "I;16N") == 0) {
+#ifdef WORDS_BIGENDIAN
+                        bigendian = 1;
+#else
+                        bigendian = 0;
+#endif
+                    } else if (strcmp(image->mode, "I;16B") == 0) {
+                        bigendian = 1;
+                    } else {
+                        bigendian = 0;
+                    }
                 }
                 for (i = x = y = 0; i < n; i++) {
                     set_value_to_item(seq, i);