add warning if font is not set

test/test_utils.py

@@ -1,4 +1,5 @@
 import os
+import re
 import sys
 import tempfile
 from io import BytesIO
@@ -168,6 +169,13 @@ def test_draw_invalid_boxes():
         utils.draw_bounding_boxes(img_correct, boxes, colors=colors_wrong)
 
 
+def test_draw_boxes_warning():
+    img = torch.full((3, 100, 100), 255, dtype=torch.uint8)
+
+    with pytest.warns(UserWarning, match=re.escape("Argument 'font_size' will be ignored since 'font' is not set.")):
+        utils.draw_bounding_boxes(img, boxes, font_size=11)
+
+
 @pytest.mark.parametrize(
     "colors",
     [

torchvision/utils.py

@@ -164,7 +164,7 @@ def draw_bounding_boxes(
     fill: Optional[bool] = False,
     width: int = 1,
     font: Optional[str] = None,
-    font_size: int = 10,
+    font_size: Optional[int] = None,
 ) -> torch.Tensor:
 
     """
@@ -223,6 +223,13 @@ def draw_bounding_boxes(
 
     colors = [(ImageColor.getrgb(color) if isinstance(color, str) else color) for color in colors]
 
+    if font is None:
+        if font_size is not None:
+            warnings.warn("Argument 'font_size' will be ignored since 'font' is not set.")
+        txt_font = ImageFont.load_default()
+    else:
+        txt_font = ImageFont.truetype(font=font, size=font_size or 10)
+
     # Handle Grayscale images
     if image.size(0) == 1:
         image = torch.tile(image, (3, 1, 1))
@@ -236,8 +243,6 @@ def draw_bounding_boxes(
     else:
         draw = ImageDraw.Draw(img_to_draw)
 
-    txt_font = ImageFont.load_default() if font is None else ImageFont.truetype(font=font, size=font_size)
-
     for bbox, color, label in zip(img_boxes, colors, labels):  # type: ignore[arg-type]
         if fill:
             fill_color = color + (100,)