# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1444341689 -7200
# Node ID 01d3243e1374045430cb063eb8e623fe2633ceb3
# Parent  a64e7a0a3d333c9be11d441671036655fdee7b7e
Attempt to find the next best combination of colours when some pixel values
cannot be represented.

diff -r a64e7a0a3d33 -r 01d3243e1374 optimiser.py
--- a/optimiser.py	Thu Oct 08 23:45:40 2015 +0200
+++ b/optimiser.py	Fri Oct 09 00:01:29 2015 +0200
@@ -24,6 +24,7 @@
 from os.path import split, splitext
 import EXIF
 import PIL.Image
+import itertools
 import math
 import sys
 
@@ -137,21 +138,25 @@
     specified 'chosen' colours.
     """
 
-    l = [(f, value) for f, value in combination(rgb) if value in chosen]
+    l = [(f, value) for f, value in combination(rgb) if not chosen or value in chosen]
     l.sort(reverse=True)
     return l
 
-def get_value(rgb, chosen=None):
+def get_value(rgb, chosen=None, fail=False):
 
     """
     Get an output colour for 'rgb', optionally limited to any specified 'chosen'
-    colours.
+    colours. If 'fail' is set to a true value, return None if the colour cannot
+    be expressed using any of the chosen colours.
     """
 
     l = pattern(rgb, chosen)
     limit = sum([f for f, c in l])
     if not limit:
-        return l[randrange(0, len(l))][1]
+        if fail:
+            return None
+        else:
+            return l[randrange(0, len(l))][1]
 
     choose = random() * limit
     threshold = 0
@@ -201,6 +206,22 @@
     c.sort(reverse=True)
     return c
 
+def get_combinations(c, n):
+
+    """
+    Get combinations of colours from 'c' of size 'n' in decreasing order of
+    probability.
+    """
+
+    all = []
+    for l in itertools.combinations(c, n):
+        total = 0
+        for f, value in l:
+            total += f
+        all.append((total, l))
+    all.sort(reverse=True)
+    return [l for total, l in all]
+
 def test():
 
     "Generate slices of the colour cube."
@@ -366,8 +387,18 @@
     if make_image:
         for y in range(0, height):
             c = get_colours(im, y)
-            most = [value for n, value in c[:4]]
-            least = [value for n, value in c[4:]]
+
+            for l in get_combinations(c, 4):
+                most = [value for f, value in l]
+                for x in range(0, width):
+                    rgb = im.getpixel((x, y))
+                    value = get_value(rgb, most, True)
+                    if value is None:
+                        break # try next combination
+                else:
+                    break # use this combination
+            else:
+                most = [value for f, value in c[:4]] # use the first four
 
             for x in range(0, width):
                 rgb = im.getpixel((x, y))