bug: fix 457 visualizer error handling

src/model_api/visualizer/primitive/polygon.py

@@ -69,8 +69,8 @@ def _get_points(self, points: list[tuple[int, int]] | None, mask: np.ndarray | N
         elif mask is not None:
             points_ = self._get_points_from_mask(mask)
         else:
-            msg = "Either points or mask should be provided."
-            raise ValueError(msg)
+            logger.warning("Neither points nor mask provided. Skipping polygon drawing.")
+            return []
         return points_
 
     def _get_points_from_mask(self, mask: np.ndarray) -> list[tuple[int, int]]:
@@ -88,8 +88,8 @@ def _get_points_from_mask(self, mask: np.ndarray) -> list[tuple[int, int]]:
             logger.warning("Multiple contours found in the mask. Using the largest one.")
             contours = sorted(contours, key=cv2.contourArea, reverse=True)
         if len(contours) == 0:
-            msg = "No contours found in the mask."
-            raise ValueError(msg)
+            logger.warning("No contours found in the mask. Skipping polygon drawing.")
+            return []
         points_ = contours[0].squeeze().tolist()
         return [tuple(point) for point in points_]
 
@@ -102,6 +102,9 @@ def compute(self, image: Image) -> Image:
         Returns:
             Image with the polygon drawn on it.
         """
+        if len(self.points) == 0:
+            return image
+
         draw = ImageDraw.Draw(image, "RGBA")
         # Draw polygon with darker edge and a semi-transparent fill.
         ink = ImageColor.getrgb(self.color)

src/model_api/visualizer/scene/detection.py

@@ -13,12 +13,14 @@
 from model_api.visualizer.primitive import BoundingBox, Label, Overlay
 
 from .scene import Scene
+from .utils import get_label_color_mapping
 
 
 class DetectionScene(Scene):
     """Detection Scene."""
 
     def __init__(self, image: Image, result: DetectionResult, layout: Union[Layout, None] = None) -> None:
+        self.color_per_label = get_label_color_mapping(result.label_names)
         super().__init__(
             base=image,
             bounding_box=self._get_bounding_boxes(result),
@@ -43,7 +45,9 @@ def _get_bounding_boxes(self, result: DetectionResult) -> list[BoundingBox]:
         for score, label_name, bbox in zip(result.scores, result.label_names, result.bboxes):
             x1, y1, x2, y2 = bbox
             label = f"{label_name} ({score:.2f})"
-            bounding_boxes.append(BoundingBox(x1=x1, y1=y1, x2=x2, y2=y2, label=label))
+            bounding_boxes.append(
+                BoundingBox(x1=x1, y1=y1, x2=x2, y2=y2, label=label, color=self.color_per_label[label_name]),
+            )
         return bounding_boxes
 
     @property

src/model_api/visualizer/scene/segmentation/instance_segmentation.py

@@ -3,7 +3,6 @@
 # Copyright (C) 2025 Intel Corporation
 # SPDX-License-Identifier: Apache-2.0
 
-import random
 from typing import Union
 
 import cv2
@@ -13,15 +12,14 @@
 from model_api.visualizer.layout import Flatten, HStack, Layout
 from model_api.visualizer.primitive import BoundingBox, Label, Overlay, Polygon
 from model_api.visualizer.scene import Scene
+from model_api.visualizer.scene.utils import get_label_color_mapping
 
 
 class InstanceSegmentationScene(Scene):
     """Instance Segmentation Scene."""
 
     def __init__(self, image: Image, result: InstanceSegmentationResult, layout: Union[Layout, None] = None) -> None:
-        # nosec as random is used for color generation
-        g = random.Random(0)  # noqa: S311 # nosec B311
-        self.color_per_label = {label: f"#{g.randint(0, 0xFFFFFF):06x}" for label in set(result.label_names)}  # nosec B311
+        self.color_per_label = get_label_color_mapping(result.label_names)
         super().__init__(
             base=image,
             label=self._get_labels(result),

src/model_api/visualizer/scene/utils.py

@@ -0,0 +1,40 @@
+"""Visualizer utilities."""
+
+# Copyright (C) 2026 Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
+
+COLOR_PALETTE = [
+    "#FF6B6B",  # Red
+    "#4ECDC4",  # Teal
+    "#45B7D1",  # Blue
+    "#FFA07A",  # Light Salmon
+    "#98D8C8",  # Mint
+    "#F7DC6F",  # Yellow
+    "#BB8FCE",  # Purple
+    "#85C1E2",  # Sky Blue
+    "#F8B739",  # Orange
+    "#52BE80",  # Green
+    "#EC7063",  # Coral
+    "#5DADE2",  # Light Blue
+    "#F39C12",  # Dark Orange
+    "#8E44AD",  # Dark Purple
+    "#16A085",  # Dark Teal
+    "#E74C3C",  # Dark Red
+    "#3498DB",  # Dodger Blue
+    "#2ECC71",  # Emerald
+    "#F1C40F",  # Sun Yellow
+    "#E67E22",  # Carrot Orange
+]
+
+
+def get_label_color_mapping(labels: list[str]) -> dict[str, str]:
+    """Generate a consistent color mapping for a list of labels.
+
+    Args:
+        labels: List of label names.
+
+    Returns:
+        Dictionary mapping each label to a hex color string.
+    """
+    unique_labels = sorted(set(labels))
+    return {label: COLOR_PALETTE[i % len(COLOR_PALETTE)] for i, label in enumerate(unique_labels)}

tests/unit/visualizer/test_primitive.py

@@ -5,7 +5,6 @@
 
 import numpy as np
 import PIL
-import pytest
 from PIL import ImageDraw
 
 from model_api.visualizer import BoundingBox, Keypoint, Label, Overlay, Polygon
@@ -58,8 +57,11 @@ def test_polygon(mock_image: PIL.Image):
     polygon = Polygon(mask=mask, color="red", opacity=1, outline_width=1)
     assert polygon.compute(mock_image) == expected_image
 
-    with pytest.raises(ValueError, match="No contours found in the mask."):
-        Polygon(mask=np.zeros((100, 100), dtype=np.uint8)).compute(mock_image)
+    # Test with empty mask - should not raise, just return image unchanged
+    empty_mask = np.zeros((100, 100), dtype=np.uint8)
+    polygon_empty = Polygon(mask=empty_mask)
+    result = polygon_empty.compute(mock_image)
+    assert result == mock_image
 
 
 def test_label(mock_image: PIL.Image):