fix(v5): preserve grayscale gradient masks

backend/processing/registry.py

@@ -327,6 +327,7 @@ def gradient_abs_sum(image, params):
     Use it to emphasize prominent edges before combining them with a sharpened image.
     """
 
+    grayscale_input = image.ndim == 2
     operator = params.get("operator", "sobel")
     gray = to_gray(image).astype(np.float32)
     if operator == "roberts":
@@ -337,7 +338,8 @@ def gradient_abs_sum(image, params):
         gy = np.array([[-1, 0, 1], [-2, 0, 2], [-1, 0, 1]], dtype=np.float32)
     fx = cv2.filter2D(gray, cv2.CV_32F, gx, borderType=cv2.BORDER_REFLECT)
     fy = cv2.filter2D(gray, cv2.CV_32F, gy, borderType=cv2.BORDER_REFLECT)
-    return gray_to_rgb(normalize_to_uint8(np.abs(fx) + np.abs(fy)))
+    gradient = normalize_to_uint8(np.abs(fx) + np.abs(fy))
+    return gradient if grayscale_input else gray_to_rgb(gradient)
 
 
 def rgb_channel(image, params):