fix_corner_markers now raises runtime †error if fewer than 3 corner markers are found

zesje/images.py

@@ -59,7 +59,7 @@ def fix_corner_markers(corner_keypoints, shape):
     """
 
     if len(corner_keypoints) == 4 or len(corner_keypoints) < 3:
-        return corner_keypoints
+        raise RuntimeError("Fewer then 3 corner markers found")
 
     x_sep = shape[1] / 2
     y_sep = shape[0] / 2

zesje/pregrader.py

@@ -22,7 +22,6 @@ def add_feedback_to_solution(sub, exam, page, page_img, corner_keypoints):
     """
     problems_on_page = [problem for problem in exam.problems if problem.widget.page == page]
 
-    # TODO: What if less than 3 keypoints are found?
     top_left_point, fixed_corner_keypoints = fix_corner_markers(corner_keypoints, page_img.shape)
 
     for problem in problems_on_page:

zesje/scans.py

@@ -339,7 +339,12 @@ def process_page(image_data, exam_config, output_dir=None, strict=False):
         return True, "Testing, image not saved and database not updated."
 
     sub, exam = update_database(image_path, barcode)
-    add_feedback_to_solution(sub, exam, barcode.page, image_array, corner_keypoints)
+
+    try:
+        add_feedback_to_solution(sub, exam, barcode.page, image_array, corner_keypoints)
+    except RuntimeError as e:
+        if strict:
+            return False, str(e)
 
     if barcode.page == 0:
         description = guess_student(