Add empty mask handling within threshold.triangle

plantcv/plantcv/threshold/threshold_methods.py

@@ -196,6 +196,13 @@ def triangle(gray_img, object_type="light", xstep=1):
     :param xstep: int
     :return bin_img: numpy.ndarray
     """
+    # If the image is empty, return empty image
+    if np.count_nonzero(gray_img) == 0:
+        params.device += 1
+        bin_img = np.copy(gray_img)
+        _debug(visual=bin_img, filename=os.path.join(params.debug_outdir, f"{params.device}_triangle_empty.png"))
+        return bin_img
+
     # Calculate automatic threshold value based on triangle algorithm
     hist = cv2.calcHist([gray_img], [0], None, [256], [0, 255])
 

tests/plantcv/threshold/test_threshold_methods.py

@@ -255,3 +255,10 @@ def test_dual_channels_bad_channel():
     pts = [(0, 0), (255, 255)]
     with pytest.raises(RuntimeError):
         _ = dual_channels(img, x_channel='wrong_ch', y_channel='index', points=pts, above=True)
+
+
+def test_empty_mask_triangle():
+    """Test for PlantCV."""
+    mask = np.zeros((100, 100), dtype=np.uint8)
+    fmask = triangle(mask)
+    assert np.sum(fmask) == 0