Added some fixes and a test

tests/test_three_corners.py

+import cv2
+import os
+import numpy as np
+
+from zesje.images import fix_corner_markers, guess_dpi
+from zesje.scans import find_corner_marker_keypoints, process_page
+
+
+def test_three_straight_corners_1():
+    shape = (240, 200, 3)
+    corner_markers = [(50, 50), (120, 50), (50, 200)]
+
+    corner_markers = fix_corner_markers(corner_markers, shape)
+
+    assert (120, 200) in corner_markers
+
+
+def test_three_straight_corners_2():
+    shape = (240, 200, 3)
+    corner_markers = [(120, 50), (50, 200), (120, 200)]
+
+    corner_markers = fix_corner_markers(corner_markers, shape)
+
+    assert (50, 50) in corner_markers
+
+
+def test_pdf(datadir):
+    # Max deviation of inferred corner marker and actual location
+    epsilon = 2
+
+    # Scan rotated image with 4 corner markers
+    image_filename1 = 'a4-rotated.png'
+    image_path = os.path.join(datadir, 'cornermarkers', image_filename1)
+    page_img = cv2.imread(image_path)
+
+    corners1 = find_corner_marker_keypoints(page_img)
+
+    # Scan the same image with 3 corner markers
+    image_filename2 = 'a4-rotated-3-markers.png'
+    image_path = os.path.join(datadir, 'cornermarkers', image_filename2)
+    page_img = cv2.imread(image_path)
+
+    corners2 = find_corner_marker_keypoints(page_img)
+
+    # Get marker that was removed
+    diff = [corner for corner in corners1 if corner not in corners2]
+    diff_marker = min(diff)
+
+    fixed_corners2 = fix_corner_markers(corners2, page_img.shape)
+    added_marker = [corner for corner in fixed_corners2 if corner not in corners2][0]
+
+    # Check if 'inferred' corner marker is not too far away
+    dist = np.linalg.norm(np.subtract(added_marker, diff_marker))
+
+    assert dist < epsilon

zesje/images.py

@@ -38,34 +38,32 @@ def get_box(image_array, box, padding=0.3):
     return image_array[top:bottom, left:right]
 
 
-def fix_corner_markers(corner_keypoints, image, image_format):
+def fix_corner_markers(corner_keypoints, shape):
     """
     Corrects the list of corner markers if only three corner markers are found.
     This function raises if only two corner keypoints are detected.
 
-    Params
-    ------
+    Parameters
+    ----------
     corner_keypoints: list of corner marker locations as tuples
-    image: the image of the page with the corner markers
+    dpi: the dpi of the image in which the corner markers are from
+
     image_format: either A4 or US letter
 
+    Returns
+    -------
+    A list of four corner markers.
+
     """
 
     if len(corner_keypoints) == 4:
-        pass
+        return corner_keypoints
 
-    # TODO: raise runtime error here?
     if len(corner_keypoints) < 3:
-        raise RuntimeError
-
-    dpi = guess_dpi(image)
-
-    # TODO: add support for US letter format
-    x_len = 210
-    y_len = 297
+        raise RuntimeError("Two or fewer corner markers detected")
 
-    x_sep = x_len / dpi * 25.4
-    y_sep = y_len / dpi * 25.4
+    x_sep = shape[1] / 2
+    y_sep = shape[0] / 2
 
     top_left = [(x, y) for x, y in corner_keypoints if x < x_sep and y < y_sep]
     bottom_left = [(x, y) for x, y in corner_keypoints if x < x_sep and y > y_sep]
@@ -77,28 +75,28 @@ def fix_corner_markers(corner_keypoints, image, image_format):
         (dx, dy) = tuple(map(sub, top_right[0], bottom_right[0]))
         top_left = tuple(map(add, bottom_left[0], (dx, dy)))
 
-        return corner_keypoints + top_left
+        return corner_keypoints + [top_left]
 
     if not bottom_left:
         # Bottom left point is missing
         (dx, dy) = tuple(map(sub, top_right[0], bottom_right[0]))
         bottom_left = tuple(map(sub, top_left[0], (dx, dy)))
 
-        return corner_keypoints + bottom_left
+        return corner_keypoints + [bottom_left]
 
     if not top_right:
         # Top right point is missing
         (dx, dy) = tuple(map(sub, top_left[0], bottom_left[0]))
         top_right = tuple(map(add, bottom_right[0], (dx, dy)))
 
-        return corner_keypoints + top_right
+        return corner_keypoints + [top_right]
 
     if not bottom_right:
         # bottom right
         (dx, dy) = tuple(map(sub, top_left[0], bottom_left[0]))
         bottom_right = tuple(map(sub, top_right[0], (dx, dy)))
 
-        return corner_keypoints + bottom_right
+        return corner_keypoints + [bottom_right]
 
 
 def box_is_filled(image_array, box_coords, padding=0.3, threshold=150, pixels=False):