✅ Fix coverage

tests/test_annotation_tilerendering.py

@@ -23,7 +23,7 @@
 from tiatoolbox.annotation import Annotation, AnnotationStore, SQLiteStore
 from tiatoolbox.tools.pyramid import AnnotationTileGenerator
 from tiatoolbox.utils.env_detection import running_on_travis
-from tiatoolbox.utils.visualization import AnnotationRenderer
+from tiatoolbox.utils.visualization import AnnotationRenderer, _find_minimum_mpp_sf
 from tiatoolbox.wsicore import wsireader
 
 RNG = np.random.default_rng(0)  # Numpy Random Generator
@@ -481,3 +481,15 @@ def color_fn(props: dict[str, str]) -> tuple[int, int, int]:
     assert num == 50  # expect 50 green objects
     _, num = label(np.array(thumb)[:, :, 2])
     assert num == 0  # expect 0 blue objects
+
+
+def test_minimum_mpp_sf() -> None:
+    """Test minimum mpp_sf."""
+    mpp_sf = _find_minimum_mpp_sf((0.5, 0.5))
+    assert mpp_sf == 1.0
+
+    mpp_sf = _find_minimum_mpp_sf((0.20, 0.20))
+    assert mpp_sf == 0.20 / 0.25
+
+    mpp_sf = _find_minimum_mpp_sf(None)
+    assert mpp_sf == 1.0

tiatoolbox/utils/visualization.py

@@ -559,6 +559,13 @@ def to_int_tuple(x: tuple[int, ...] | np.ndarray) -> tuple[int, ...]:
     return canvas
 
 
+def _find_minimum_mpp_sf(mpp: tuple[float, float]) -> float:
+    """Calculates minimum mpp scale factor."""
+    if mpp is not None:
+        return np.minimum(mpp[0] / 0.25, 1)
+    return 1.0
+
+
 class AnnotationRenderer:
     """Renders AnnotationStore to a tile.
 
@@ -971,9 +978,7 @@ def render_annotations(
             int((bounds[2] - bounds[0]) / scale),
         ]
 
-        mpp_sf = 1
-        if self.info["mpp"] is not None:
-            mpp_sf = np.minimum(self.info["mpp"][0] / 0.25, 1)
+        mpp_sf = _find_minimum_mpp_sf(self.info["mpp"])
 
         min_area = 0.0005 * (output_size[0] * output_size[1]) * (scale * mpp_sf) ** 2