modif ImageVerification() -> no image constant + some changes in the dimension verif

brick/processing/input.py

@@ -37,29 +37,37 @@ from PIL.ExifTags import TAGS
 
 
 def ImageVerification(image: array_t, channel: str) -> array_t:
-    if image.ndim == 3:
+    #
+    # The image must not be constant
+    if image.max() == image.min():
+        raise ValueError('The input image should not be constant.')
+
+    # Verification of the dimension of the image and its coherence with the parameters (channel)
+    elif image.ndim == 3:
         print('Your image has only one color channel.')
-        if channel == 'RGB':
-            print('"RGB" channels are specified in the parameters. The image dimensions are not correct:', image.ndim,
-                  ', instead of 4.')
-            sy_.exit(0)
+        if channel is not None:
+            raise ValueError('The image has only 3 dimensions. However, a value for the "channel" parameter is '
+                             'specified. Give the channel the value None')
 
     elif image.ndim == 4:
         if channel == 'R' or channel == 'G' or channel == 'B':
+            # not changed into if --channel in 'RGB'-- because if channel='RG' => True.
             print('The image has multiple color channels. The channel', channel,
                   'is specified in the parameters.')
-            for idx, color in enumerate('RGB'):
-                if channel == color:
-                    image = image[:, :, :, idx]
+            image = image[:, :, :, 'RGB'.find(channel)]
+
+            # The obtained image must not be constant
+            if image.max() == image.min():
+                raise ValueError('The input image should not be constant.')
+
             return image
-        elif channel == 'RGB':
-            print('"RGB" channels are specified in the parameters. The program does not handle multiple channels for '
-                  'now.')
-            sy_.exit(0)
+        
+        else:
+            raise ValueError('The image has multiple color channels. Error in the value of the parameter channel.')
 
     elif image.ndim != 4 and image.ndim != 3:
-        print('The image dimensions are not correct:', image.ndim, ', instead of 3 or 4.')
-        sy_.exit(0)
+        raise ValueError(f'The image dimensions are not correct: {image.ndim}, instead of 3 or 4.')
+
 
 
 # if channel != 'RGB' and image.ndim == 4: