Account for dtype in the pixel array so the maximum value stays corre…

…ct in the invert function (ManimCommunity#3493)

* fix(lib): fix

This fixes an issue where the `invert` argument would only work for `uint8` dtypes. Now the `max` value is updated according to the pixel array dtype.

Maybe we should add unit tests for that, but haven't found an obvious place to put unit tests.

* chore(ci): add basic test

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix(ci): wrong attr name

* Update tests/module/mobject/test_image.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Benjamin Hackl <[email protected]>

manim/mobject/types/image_mobject.py

@@ -191,7 +191,9 @@ def __init__(
             self.pixel_array, self.pixel_array_dtype
         )
         if self.invert:
-            self.pixel_array[:, :, :3] = 255 - self.pixel_array[:, :, :3]
+            self.pixel_array[:, :, :3] = (
+                np.iinfo(self.pixel_array_dtype).max - self.pixel_array[:, :, :3]
+            )
         super().__init__(scale_to_resolution, **kwargs)
 
     def get_pixel_array(self):

tests/module/mobject/test_image.py

@@ -0,0 +1,14 @@
+import numpy as np
+import pytest
+
+from manim import ImageMobject
+
+
+@pytest.mark.parametrize("dtype", [np.uint8, np.uint16])
+def test_invert_image(dtype):
+    array = (255 * np.random.rand(10, 10, 4)).astype(dtype)
+    image = ImageMobject(array, pixel_array_dtype=dtype, invert=True)
+    assert image.pixel_array.dtype == dtype
+
+    array[:, :, :3] = np.iinfo(dtype).max - array[:, :, :3]
+    assert np.allclose(array, image.pixel_array)