image_as_rgb correctly handles images that are already RGB

src/colonyscanalyser/imaging.py

@@ -254,7 +254,10 @@ def image_as_rgb(image: ndarray) -> ndarray:
         return gray2rgb(image)
 
     # Remove alpha channel if present
-    return rgba2rgb(image)
+    if image.shape[-1] == 4:
+        image = rgba2rgb(image)
+
+    return image
 
 
 def remove_background_mask(image: ndarray, smoothing: float = 1, sigmoid_cutoff: float = 0.4, **filter_args) -> ndarray:

tests/unit/test_imaging.py

@@ -226,6 +226,17 @@ def test_grayscale(self, image):
         assert len(result.shape) == 3
         assert result.shape[-1] == 3
 
+    def test_rgb(self, image):
+        from numpy import empty
+
+        image = empty(image.shape + (3, ), dtype = image.dtype)
+        result = image_as_rgb(image)
+
+        assert len(image.shape) == 3
+        assert image.shape[-1] == 3
+        assert len(result.shape) == 3
+        assert result.shape[-1] == 3
+
     def test_rgba(self, image):
         from numpy import empty