Update arg help message and fix test

Author: Dmitry Sidnev

demos/background_subtraction_demo/python/README.md

@@ -133,7 +133,9 @@ Options:
                         output (by default to green field).
   --background BACKGROUND
                         Optional. Background image for background-matting
-                        model.
+                        model. This is a background image that equal to a real
+                        background behind a person on an input frame and must
+                        have the same shape as an input image.
   --blur_bgr BLUR_BGR   Optional. Background blur strength (by default with
                         value 0 is not applied).
 

demos/background_subtraction_demo/python/background_subtraction_demo.py

@@ -63,7 +63,9 @@ def build_argparser():
     args.add_argument('--target_bgr', default=None, type=str,
                       help='Optional. Background onto which to composite the output (by default to green field).')
     args.add_argument('--background', default=None, type=str,
-                      help='Optional. Background image for background-matting model.')
+                      help='Optional. Background image for background-matting model. This is a background image '
+                           'that equal to a real background behind a person on an input frame and must have the '
+                           'same shape as an input image.')
     args.add_argument('--blur_bgr', default=0, type=int,
                       help='Optional. Background blur strength (by default with value 0 is not applied).')
 

demos/tests/cases.py

@@ -715,7 +715,7 @@ def single_option_cases(key, *args):
         TestCase(options={'--no_show': None,
             **MONITORS,
             '-i': DataPatternArg('instance-segmentation'),
-            '--bgr': DataPatternArg('instance-segmentation'),
+            '--background': DataPatternArg('instance-segmentation'),
         }),
         single_option_cases('-m',
             ModelArg('instance-segmentation-person-0007'),