1.1 --- a/optimiser.py	Sat Oct 10 16:39:08 2015 +0200
     1.2 +++ b/optimiser.py	Sat Oct 10 16:41:10 2015 +0200
     1.3 @@ -82,7 +82,7 @@
     1.4      step = half_resolution_preview and 2 or 1
     1.5  
     1.6      for y in range(0, height):
     1.7 -        for x in range(0, width):
     1.8 +        for x in range(0, width, step):
     1.9              rgb = im.getpixel((x, y))
    1.10              value = get_value(rgb)
    1.11              im.putpixel((x, y), value)