Change grid colour threshold detection method.

home/xword.py

@@ -1,3 +1,4 @@
+import itertools
 import math
 import cv2
 import numpy as np
@@ -152,6 +153,18 @@ def extract_grid_colours(img, num_rows, num_cols, sampling_block_size_ratio):
     return grid
 
 
+def get_grid_colour_threshold(grid_colours):
+    pixels = sorted(itertools.chain.from_iterable(grid_colours))
+    delta_max = -1
+    i_max = -1
+    for i in range(1, len(pixels)):
+        delta = pixels[i] - pixels[i - 1]
+        if delta > delta_max:
+            delta_max = delta
+            i_max = i
+    return (pixels[i_max] + pixels[i_max - 1]) / 2
+
+
 def grid_colours_to_blocks(grid_colours, num_rows, num_cols, sampling_threshold):
     grid = copy.deepcopy(grid_colours)
     warning = False
@@ -246,13 +259,14 @@ def extract_crossword_grid(
         warnings.append("Crossword is not square")
 
     block_img = extract_square(original, top_left, top_right, bottom_right, bottom_left)
+    grid_colours = extract_grid_colours(block_img, num_rows, num_cols, sampling_block_size_ratio)
 
     if sampling_threshold is None:
-        sampling_threshold = get_threshold_from_quantile(block_img, sampling_threshold_quantile)
+        #sampling_threshold = get_threshold_from_quantile(block_img, sampling_threshold_quantile)
+        sampling_threshold = get_grid_colour_threshold(grid_colours)
     else:
         sampling_threshold = sampling_threshold
 
-    grid_colours = extract_grid_colours(block_img, num_rows, num_cols, sampling_block_size_ratio)
     warning, grid = grid_colours_to_blocks(grid_colours, num_rows, num_cols, sampling_threshold)
     if warning:
         warnings.append("Some blocks may be the wrong colour")