# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1443717599 -7200
# Node ID cd815af3effc57bd3a92b4861b7bb293ac104af3
# Parent  c768f24e5233faecb78a5fa97f1759bed9c2baac
Reduced the frequency of the second colour in the dithering pattern.
Added preview image generation support.

diff -r c768f24e5233 -r cd815af3effc optimiser.py
--- a/optimiser.py	Thu Oct 01 12:50:55 2015 +0200
+++ b/optimiser.py	Thu Oct 01 18:39:59 2015 +0200
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 
-from itertools import combinations
 from random import randint
+from os.path import extsep, splitext
 import EXIF
 import PIL.Image
 import math
@@ -50,8 +50,8 @@
     return start, end, f
 
 def choose(seq, f):
-    last = int(seq * math.sqrt(f))
-    current = int((seq + 1) * math.sqrt(f))
+    last = int(seq * f)
+    current = int((seq + 1) * f)
     return last != current
 
 def get_value(xy, rgb, width, height, values=None):
@@ -116,6 +116,10 @@
     height = 256
 
     input_filename, output_filename = sys.argv[1:3]
+    basename, ext = splitext(output_filename)
+    preview_filename = extsep.join([basename + "_preview", ext])
+
+    preview = "-p" in sys.argv[3:]
     rotate = "-r" in sys.argv[3:]
     saturate = sys.argv[3:].count("-s")
     desaturate = sys.argv[3:].count("-d")
@@ -124,6 +128,9 @@
     im = PIL.Image.open(input_filename)
     im = rotate_and_scale(im, width, height, rotate)
 
+    if preview:
+        im_preview = im.copy()
+
     width, height = im.size
 
     colours = []
@@ -147,10 +154,16 @@
             else:
                 c[value] += 1
 
+            if preview:
+                im_preview.putpixel((x, y), value)
+
         c = [(n, value) for value, n in c.items()]
         c.sort(reverse=True)
         colours.append(c)
 
+    if preview:
+        im_preview.save(preview_filename)
+
     for y, c in enumerate(colours):
         most = [value for n, value in c[:4]]
         least = [value for n, value in c[4:]]