Add test function and update cli docs

docs/guides/cli.md

@@ -389,6 +389,9 @@ optional arguments:
   --distinctly_color DISTINCTLY_COLOR
                         Specify how to color instances. Options include: "instances",
                         "edges", and "nodes" (default: "instances")
+  --background BACKGROUND
+                        Specify the type of background to be used to save the videos.
+                        Options: original, black, white and grey. (default: "original")
 ```
 
 ## Debugging

sleap/io/visuals.py

@@ -32,7 +32,7 @@ def reader(
     video: Video,
     frames: List[int],
     scale: float = 1.0,
-    background="Original",
+    background: str = "original",
 ):
     """Read frame images from video and send them into queue.
 
@@ -48,6 +48,7 @@ def reader(
         None.
     """
 
+    background = background.lower()
     cv2.setNumThreads(usable_cpu_count())
 
     total_count = len(frames)
@@ -71,15 +72,17 @@ def reader(
             loaded_chunk_idxs, video_frame_images = video.get_frames_safely(
                 frames_idx_chunk
             )
-            if background != "Original":
+            if background != "original":
                 # fill the frame with the color
-                if background == "Black":
+                if background == "black":
                     fill = 0
-                elif background == "Grey":
+                elif background == "grey":
                     fill = 127
-                else:
+                elif background == "white":
                     # background == White
                     fill = 255
+                else:
+                    raise ValueError(f"Invalid background color: {background}")
                 video_frame_images = video_frame_images * 0 + fill
 
             if not loaded_chunk_idxs:
@@ -514,7 +517,7 @@ def save_labeled_video(
     fps: int = 15,
     scale: float = 1.0,
     crop_size_xy: Optional[Tuple[int, int]] = None,
-    background: str = "Original",
+    background: str = "original",
     show_edges: bool = True,
     edge_is_wedge: bool = False,
     marker_size: int = 4,
@@ -714,6 +717,15 @@ def main(args: list = None):
             "and 'nodes' (default: 'nodes')"
         ),
     )
+    parser.add_argument(
+        "--background",
+        type=str,
+        default="original",
+        help=(
+            "Specify the type of background to be used to save the videos."
+            "Options for background: original, black, white and grey"
+        ),
+    )
     args = parser.parse_args(args=args)
     labels = Labels.load_file(
         args.data_path, video_search=[os.path.dirname(args.data_path)]
@@ -749,6 +761,7 @@ def main(args: list = None):
         marker_size=args.marker_size,
         palette=args.palette,
         distinctly_color=args.distinctly_color,
+        background=args.background,
     )
 
     print(f"Video saved as: {filename}")

tests/io/test_visuals.py

@@ -63,6 +63,16 @@ def test_serial_pipeline(centered_pair_predictions, tmpdir):
     )
 
 
+@pytest.mark.parametrize("background", ["original", "black", "white", "grey"])
+def test_sleap_render_with_different_backgrounds(background):
+    args = (
+        f"-o test_{background}.avi -f 2 --scale 1.2 --frames 1,2 --video-index 0 --background {background} "
+        "tests/data/json_format_v2/centered_pair_predictions.json".split()
+    )
+    sleap_render(args)
+    assert os.path.exists(f"test_{background}.avi")
+
+
 def test_sleap_render(centered_pair_predictions):
     args = (
         "-o testvis.avi -f 2 --scale 1.2 --frames 1,2 --video-index 0 "