Fix IndexError when calling hough_line_peaks with too few angles (sci…

…kit-image#5024)

Fixes scikit-imagegh-4814

Co-authored-by: Riadh Fezzani <rfezzani@gmail.com>

skimage/transform/hough_transform.py

@@ -58,6 +58,7 @@ def hough_line_peaks(hspace, angles, dists, min_distance=9, min_angle=10,
     """
     from ..feature.peak import _prominent_peaks
 
+    min_angle = min(min_angle, hspace.shape[1])
     h, a, d = _prominent_peaks(hspace, min_xdistance=min_angle,
                                min_ydistance=min_distance,
                                threshold=threshold,

skimage/transform/tests/test_hough_transform.py

@@ -180,6 +180,15 @@ def test_hough_line_peaks_zero_input():
     assert_equal(a, np.array([]))
 
 
+def test_hough_line_peaks_single_angle():
+    # Regression test for gh-4814
+    # This code snippet used to raise an IndexError
+    img = np.random.random((100, 100))
+    tested_angles = np.array([np.pi / 2])
+    h, theta, d = transform.hough_line(img, theta=tested_angles)
+    accum, angles, dists = transform.hough_line_peaks(h, theta, d, threshold=2)
+
+
 @test_parallel()
 def test_hough_circle():
     # Prepare picture