fixed image cropping bug (that was introducing an offset compared to the TechDraw view)

ahb_raster_view.py

@@ -252,8 +252,9 @@ class RasterView:
 		# Crop the image, which is also used to deduce the center of the source view
 		original_size = composite_img.size
 		
-		bg = Image.new(composite_img.mode, composite_img.size, '#ffffff') # fills an image with the background color
-		diff = ImageChops.difference(composite_img, bg) # diff between the actual image and the background color
+		diff_source_img = composite_img.split()[3]
+		bg = Image.new(diff_source_img.mode, diff_source_img.size, '#000000') # fills an image with the background color
+		diff = ImageChops.difference(diff_source_img, bg) # diff between the actual image and the background color
 		bbox = diff.getbbox() # finds border size (non-black portion of the image)
 		composite_img = composite_img.crop(bbox)