Fix _brightness_contrast_adjust_uint when beta_by_max = True (#487)

Co-authored-by: druzhinin <druzhinin@simicon.com>
Co-authored-by: Mikhail Druzhinin <dipet@gmail.com>

albumentations/augmentations/functional.py

@@ -1298,7 +1298,7 @@ def _brightness_contrast_adjust_uint(img, alpha=1, beta=0, beta_by_max=False):
         if beta_by_max:
             lut += beta * max_value
         else:
-            lut += beta * np.mean(img)
+            lut += (alpha * beta) * np.mean(img)
 
     lut = np.clip(lut, 0, max_value).astype(dtype)
     img = cv2.LUT(img, lut)

tests/test_functional.py

@@ -986,3 +986,19 @@ def test_normalize_np_cv_equal(image, mean, std):
     res1 = F.normalize_cv2(image, mean, std)
     res2 = F.normalize_numpy(image, mean, std)
     assert np.allclose(res1, res2)
+
+
+@pytest.mark.parametrize("beta_by_max", [True, False])
+def test_brightness_contrast_adjust_equal(beta_by_max):
+    image_int = np.random.randint(0, 256, [512, 512, 3], dtype=np.uint8)
+    image_float = image_int.astype(np.float32) / 255
+
+    alpha = 1.3
+    beta = 0.14
+
+    image_int = F.brightness_contrast_adjust(image_int, alpha, beta, beta_by_max)
+    image_float = F.brightness_contrast_adjust(image_float, alpha, beta, beta_by_max)
+
+    image_float = (image_float * 255).astype(int)
+
+    assert np.abs(image_int.astype(int) - image_float).max() <= 1