1 #!/usr/bin/env python 2 3 """ 4 Convert and optimise images for display in an Acorn Electron MODE 1 variant 5 with four colours per line but eight colours available for selection on each 6 line. 7 8 Copyright (C) 2015 Paul Boddie <paul@boddie.org.uk> 9 10 This program is free software; you can redistribute it and/or modify it under 11 the terms of the GNU General Public License as published by the Free Software 12 Foundation; either version 3 of the License, or (at your option) any later 13 version. 14 15 This program is distributed in the hope that it will be useful, but WITHOUT ANY 16 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 17 PARTICULAR PURPOSE. See the GNU General Public License for more details. 18 19 You should have received a copy of the GNU General Public License along 20 with this program. If not, see <http://www.gnu.org/licenses/>. 21 """ 22 23 from random import random, randrange 24 import itertools 25 import math 26 27 corners = [ 28 (0, 0, 0), (255, 0, 0), (0, 255, 0), (255, 255, 0), 29 (0, 0, 255), (255, 0, 255), (0, 255, 255), (255, 255, 255) 30 ] 31 32 # Basic colour operations. 33 34 def within(v, lower, upper): 35 return min(max(v, lower), upper) 36 37 def clip(v): 38 return int(within(v, 0, 255)) 39 40 def distance(rgb1, rgb2): 41 return math.sqrt(pow(abs(rgb1[0] - rgb2[0]), 2) + pow(abs(rgb1[1] - rgb2[1]), 2) + pow(abs(rgb1[2] - rgb2[2]), 2)) 42 43 def restore(srgb): 44 r, g, b = srgb 45 return int(r * 255.0), int(g * 255.0), int(b * 255.0) 46 47 def scale(rgb): 48 r, g, b = rgb 49 return r / 255.0, g / 255.0, b / 255.0 50 51 def invert(srgb): 52 r, g, b = srgb 53 return 1.0 - r, 1.0 - g, 1.0 - b 54 55 scaled_corners = map(scale, corners) 56 zipped_corners = zip(corners, scaled_corners) 57 58 # Colour distribution functions. 59 60 def combination(rgb): 61 62 "Return the colour distribution for 'rgb'." 63 64 # Get the colour with components scaled from 0 to 1, plus the inverted 65 # component values. 66 67 srgb = scale(rgb) 68 rgbi = invert(srgb) 69 pairs = zip(rgbi, srgb) 70 71 # For each corner of the colour cube (primary and secondary colours plus 72 # black and white), calculate the corner value's contribution to the 73 # input colour. 74 75 d = [] 76 for corner, scaled in zipped_corners: 77 rs, gs, bs = scaled 78 79 # Obtain inverted channel values where corner channels are low; 80 # obtain original channel values where corner channels are high. 81 82 d.append((pairs[0][int(rs)] * pairs[1][int(gs)] * pairs[2][int(bs)], corner)) 83 84 # Balance the corner contributions. 85 86 return balance(d) 87 88 def complements(rgb): 89 90 "Return 'rgb' and its complement." 91 92 r, g, b = rgb 93 return rgb, restore(invert(scale(rgb))) 94 95 bases = [(0, 0, 0), (255, 0, 0), (0, 255, 0), (0, 0, 255)] 96 base_complements = map(complements, bases) 97 98 def balance(d): 99 100 """ 101 Balance distribution 'd', cancelling opposing values and their complements 102 and replacing their common contributions with black and white contributions. 103 """ 104 105 d = dict([(value, f) for f, value in d]) 106 for primary, secondary in base_complements: 107 common = min(d[primary], d[secondary]) 108 d[primary] -= common 109 d[secondary] -= common 110 return [(f, value) for value, f in d.items()] 111 112 def combine(d): 113 114 "Combine distribution 'd' to get a colour value." 115 116 out = [0, 0, 0] 117 for v, rgb in d: 118 out[0] += v * rgb[0] 119 out[1] += v * rgb[1] 120 out[2] += v * rgb[2] 121 return tuple(map(int, out)) 122 123 def pattern(rgb, chosen=None): 124 125 """ 126 Obtain a sorted colour distribution for 'rgb', optionally limited to any 127 specified 'chosen' colours. 128 """ 129 130 l = [(f, value) for f, value in combination(rgb) if not chosen or value in chosen] 131 l.sort(reverse=True) 132 return l 133 134 def get_value(rgb, chosen=None, fail=False): 135 136 """ 137 Get an output colour for 'rgb', optionally limited to any specified 'chosen' 138 colours. If 'fail' is set to a true value, return None if the colour cannot 139 be expressed using any of the chosen colours. 140 """ 141 142 l = pattern(rgb, chosen) 143 limit = sum([f for f, c in l]) 144 if not limit: 145 if fail: 146 return None 147 else: 148 return l[randrange(0, len(l))][1] 149 150 choose = random() * limit 151 threshold = 0 152 for f, c in l: 153 threshold += f 154 if choose < threshold: 155 return c 156 return c 157 158 # Colour processing operations. 159 160 def sign(x): 161 return x >= 0 and 1 or -1 162 163 def saturate_rgb(rgb, exp): 164 r, g, b = rgb 165 return saturate_value(r, exp), saturate_value(g, exp), saturate_value(b, exp) 166 167 def saturate_value(x, exp): 168 return int(127.5 + sign(x - 127.5) * 127.5 * pow(abs(x - 127.5) / 127.5, exp)) 169 170 def amplify_rgb(rgb, exp): 171 r, g, b = rgb 172 return amplify_value(r, exp), amplify_value(g, exp), amplify_value(b, exp) 173 174 def amplify_value(x, exp): 175 return int(pow(x / 255.0, exp) * 255.0) 176 177 # Image operations. 178 179 def get_colours(im, y): 180 181 "Get a colour distribution from image 'im' for the row 'y'." 182 183 width, height = im.size 184 c = {} 185 x = 0 186 while x < width: 187 rgb = im.getpixel((x, y)) 188 189 # Sum the colour probabilities. 190 191 for f, value in combination(rgb): 192 if not c.has_key(value): 193 c[value] = f 194 else: 195 c[value] += f 196 197 x += 1 198 199 d = [(n/width, value) for value, n in c.items()] 200 d.sort(reverse=True) 201 return d 202 203 def get_combinations(c, n): 204 205 """ 206 Get combinations of colours from 'c' of size 'n' in decreasing order of 207 probability. 208 """ 209 210 all = [] 211 for l in itertools.combinations(c, n): 212 total = 0 213 for f, value in l: 214 total += f 215 all.append((total, l)) 216 all.sort(reverse=True) 217 return [l for total, l in all] 218 219 def count_colours(im, colours): 220 221 """ 222 Count colours on each row of image 'im', returning a tuple indicating the 223 first row with more than the given number of 'colours' together with the 224 found colours; otherwise returning None. 225 """ 226 227 width, height = im.size 228 229 y = 0 230 while y < height: 231 l = set() 232 x = 0 233 while x < width: 234 l.add(im.getpixel((x, y))) 235 x += 1 236 if len(l) > colours: 237 return (y, l) 238 y += 1 239 return None 240 241 def process_image(pim, saturate, desaturate, darken, brighten): 242 243 """ 244 Process image 'pim' using the given options: 'saturate', 'desaturate', 245 'darken', 'brighten'. 246 """ 247 248 width, height = pim.size 249 im = SimpleImage(list(pim.getdata()), pim.size) 250 251 if saturate or desaturate or darken or brighten: 252 y = 0 253 while y < height: 254 x = 0 255 while x < width: 256 rgb = im.getpixel((x, y)) 257 if saturate or desaturate: 258 rgb = saturate_rgb(rgb, saturate and 0.5 / saturate or 2 * desaturate) 259 if darken or brighten: 260 rgb = amplify_rgb(rgb, brighten and 0.5 / brighten or 2 * darken) 261 im.putpixel((x, y), rgb) 262 x += 1 263 y += 1 264 265 pim.putdata(im.getdata()) 266 267 def convert_image(pim, colours, least_error=False): 268 269 "Convert image 'pim' to an appropriate output representation." 270 271 width, height = pim.size 272 im = SimpleImage(list(pim.getdata()), pim.size) 273 274 y = 0 275 while y < height: 276 c = get_colours(im, y) 277 278 suggestions = [] 279 280 for l in get_combinations(c, colours): 281 most = [value for f, value in l] 282 error = 0 283 284 x = 0 285 while x < width: 286 rgb = im.getpixel((x, y)) 287 value = get_value(rgb, most) 288 if least_error: 289 error += distance(value, rgb) 290 elif value is None: 291 error += 1 292 x += 1 293 294 if not least_error and not error: 295 break # use this combination 296 297 suggestions.append((error, l)) 298 299 # Find the most accurate suggestion. 300 301 else: 302 suggestions.sort() 303 most = [value for f, value in suggestions[0][1]] # get the combination 304 305 x = 0 306 while x < width: 307 rgb = im.getpixel((x, y)) 308 value = get_value(rgb, most) 309 im.putpixel((x, y), value) 310 311 if x < width - 1: 312 rgbn = im.getpixel((x+1, y)) 313 rgbn = ( 314 clip(rgbn[0] + (rgb[0] - value[0]) / 4.0), 315 clip(rgbn[1] + (rgb[1] - value[1]) / 4.0), 316 clip(rgbn[2] + (rgb[2] - value[2]) / 4.0) 317 ) 318 im.putpixel((x+1, y), rgbn) 319 320 if y < height - 1: 321 rgbn = im.getpixel((x, y+1)) 322 rgbn = ( 323 clip(rgbn[0] + (rgb[0] - value[0]) / 2.0), 324 clip(rgbn[1] + (rgb[1] - value[1]) / 2.0), 325 clip(rgbn[2] + (rgb[2] - value[2]) / 2.0) 326 ) 327 im.putpixel((x, y+1), rgbn) 328 329 x += 1 330 331 y += 1 332 333 pim.putdata(im.getdata()) 334 335 class SimpleImage: 336 337 "An image behaving like PIL.Image." 338 339 def __init__(self, data, size): 340 self.data = data 341 self.width, self.height = self.size = size 342 343 def copy(self): 344 return SimpleImage(self.data[:], self.size) 345 346 def getpixel(self, xy): 347 x, y = xy 348 return self.data[y * self.width + x] 349 350 def putpixel(self, xy, value): 351 x, y = xy 352 self.data[y * self.width + x] = value 353 354 def getdata(self): 355 return self.data 356 357 # vim: tabstop=4 expandtab shiftwidth=4