fix(converter): validate scale factor finiteness and guard against below-1-pixel dimensions in ImageResizingConverter

pyrit/converter/image_resizing_converter.py

@@ -2,6 +2,7 @@
 # Licensed under the MIT license.
 
 import logging
+import math
 from typing import Literal
 
 from PIL import Image
@@ -44,10 +45,10 @@ def __init__(
                 Defaults to 0.5 (halve the image dimensions).
 
         Raises:
-            ValueError: If unsupported output format is specified, or if scale factor is not positive.
+            ValueError: If unsupported output format is specified, or if scale factor is not a positive finite number.
         """
-        if scale_factor <= 0:
-            raise ValueError(f"Scale factor must be positive, got {scale_factor}")
+        if not math.isfinite(scale_factor) or scale_factor <= 0:
+            raise ValueError(f"Scale factor must be a positive finite number, got {scale_factor}")
         self._scale_factor = scale_factor
         super().__init__(output_format=output_format)
 
@@ -74,7 +75,14 @@ def _apply_transform(self, image: Image.Image) -> Image.Image:
 
         Returns:
             PIL.Image.Image: The resized image.
+
+        Raises:
+            ValueError: If the resizing would result in invalid dimensions (less than 1 pixel).
         """
         new_width = int(image.width * self._scale_factor)
         new_height = int(image.height * self._scale_factor)
+        if new_width < 1 or new_height < 1:
+            raise ValueError(
+                f"Resizing would result in invalid dimensions (less than 1 pixel): {new_width}x{new_height}"
+            )
         return image.resize((new_width, new_height), Image.Resampling.LANCZOS)

tests/unit/converter/test_image_resizing_converter.py

@@ -52,8 +52,8 @@ def test_image_resizing_converter_initialization_output_format_validation():
 
 def test_image_resizing_converter_initialization_scale_factor_validation():
     """Test validation of scale_factor parameter."""
-    for invalid_scale_factor in [0.0, -0.1, -1.0, -100.0]:
-        with pytest.raises(ValueError, match="Scale factor must be positive"):
+    for invalid_scale_factor in [0.0, -0.1, -1.0, -100.0, float("nan"), float("inf"), float("-inf")]:
+        with pytest.raises(ValueError, match="Scale factor must be a positive finite number"):
             ImageResizingConverter(scale_factor=invalid_scale_factor)
 
     for valid_scale_factor in [0.1, 0.5, 1.0, 2.0, 10.0]:
@@ -229,3 +229,12 @@ async def test_image_resizing_converter_output_dimensions(sample_image_bytes):
     expected_width = int(original_size[0] * scale_factor)
     expected_height = int(original_size[1] * scale_factor)
     assert resized_image.size == (expected_width, expected_height)
+
+
+def test_image_resizing_converter_invalid_dimensions():
+    """Test that scale factor yielding zero dimensions raises ValueError."""
+    converter = ImageResizingConverter(scale_factor=0.5)
+    # A 1x1 image scaled by 0.5 becomes 0x0
+    image = Image.new("RGB", (1, 1))
+    with pytest.raises(ValueError, match="Resizing would result in invalid dimensions"):
+        converter._apply_transform(image)