Feature/precise positioning

This MR adds the precise positioning functionality of OpenCV found by @hleistra as a function and includes tests for this function. The way the function works is as follows: the function takes an image and optionally the corner points of either the image itself or reference image or both. it then warps the image so that the corner markers align with the reference markers. It finishes by returning the image and new corner markers. This function makes use of the fix_corner_markers function as it needs 4 points to work. A slight change has been made to fix_corner_markers to now insert the corner markers at the right index of the list.

tests/test_scans.py

@@ -3,6 +3,7 @@ import os
 import pytest
 import numpy as np
 import PIL.Image
+import cv2
 from tempfile import NamedTemporaryFile
 from flask import Flask
 from io import BytesIO
@@ -280,3 +281,25 @@ def test_image_extraction(datadir, filename):
         assert img is not None
         assert np.average(np.array(img)) == 255
     assert page == 2
+
+
+@pytest.mark.parametrize('file_name', ["a4-rotated.png", "a4-3-markers.png", "a4-rotated-3-markers.png"])
+def test_realign_image(datadir, file_name):
+    dir_name = "cornermarkers"
+    epsilon = 2
+
+    test_file = os.path.join(datadir, dir_name, file_name)
+    test_image = np.array(PIL.Image.open(test_file))
+
+    correct_file = os.path.join(datadir, dir_name, "a4.png")
+    correct_image = cv2.imread(correct_file)
+
+    correct_corner_markers = scans.find_corner_marker_keypoints(correct_image)
+
+    result_image, result_corner_markers = scans.realign_image(test_image)
+
+    assert result_corner_markers is not None
+    for i in range(4):
+        diff = np.absolute(np.subtract(correct_corner_markers[i], result_corner_markers[i]))
+        assert diff[0] < epsilon
+        assert diff[1] < epsilon