ignore 2% of pixels near edges and don't crop more than 10% per edge (#1044)

* max crop and ignore edges

* make edge_bbox neater

kindlecomicconverter/image.py

@@ -429,6 +429,10 @@ class ComicPage:
         bbox = get_bbox_crop_margin(self.image, power, self.fill)
         
         if bbox:
+            w, h = self.image.size
+            left, upper, right, lower = bbox
+            # don't crop more than 10% of image
+            bbox = (min(0.1*w, left), min(0.1*h, upper), max(0.9*w, right), max(0.9*h, lower))
             self.maybeCrop(bbox, minimum)
 
     def cropInterPanelEmptySections(self, direction):

kindlecomicconverter/page_number_crop_alg.py

@@ -142,6 +142,21 @@ def get_bbox_crop_margin(img, power=1, background_color='white'):
     threshold = threshold_from_power(power)
     bw_img = img.point(lambda p: 255 if p <= threshold else 0)
     
+    # ignore pixels near the edges
+    w, h = bw_img.size
+    edge_bbox = [
+        (0, 0, w, int(0.02 * h)),
+        (0, int(0.98 * h), w, h),
+        (0, 0, int(0.02 * w), h),
+        (int(0.98 * w), 0, w, h)
+    ]
+    for box in edge_bbox:
+        edge = bw_img.crop(box)
+        h = edge.histogram()
+        imperfections = h[255] / (edge.height * edge.width)
+        if imperfections > 0 and imperfections < .02:
+            bw_img.paste(im=0, box=box)
+
     return bw_img.getbbox()