/* * libpipi Pathetic image processing interface library * Copyright (c) 2004-2008 Sam Hocevar * All Rights Reserved * * \$Id\$ * * This library is free software. It comes without any warranty, to * the extent permitted by applicable law. You can redistribute it * and/or modify it under the terms of the Do What The Fuck You Want * To Public License, Version 2, as published by Sam Hocevar. See * http://sam.zoy.org/wtfpl/COPYING for more details. */ /* * ostromoukhov.c: Ostromoukhov dithering functions * * This module implements Ostromoukhov's simple error diffusion algorithm, * as introduced in the paper "A Simple and Efficient Error-Diffusion * Algorithm", Proceedings of SIGGRAPH 2001, in ACM Computer Graphics, * Annual Conference Series, pp. 567--572, 2001. * * TODO: the table is actually a piecewise linear function, so it should * be easy to change it into something that works perfectly with floats. */ #include "config.h" #include "pipi.h" #include "pipi_internals.h" static int const table[][3] = { {13, 0, 5}, {13, 0, 5}, {21, 0, 10}, {7, 0, 4}, {8, 0, 5}, {47, 3, 28}, {23, 3, 13}, {15, 3, 8}, {22, 6, 11}, {43, 15, 20}, {7, 3, 3}, {501, 224, 211}, {249, 116, 103}, {165, 80, 67}, {123, 62, 49}, {489, 256, 191}, {81, 44, 31}, {483, 272, 181}, {60, 35, 22}, {53, 32, 19}, {237, 148, 83}, {471, 304, 161}, {3, 2, 1}, {481, 314, 185}, {354, 226, 155}, {1389, 866, 685}, {227, 138, 125}, {267, 158, 163}, {327, 188, 220}, {61, 34, 45}, {627, 338, 505}, {1227, 638, 1075}, {20, 10, 19}, {1937, 1000, 1767}, {977, 520, 855}, {657, 360, 551}, {71, 40, 57}, {2005, 1160, 1539}, {337, 200, 247}, {2039, 1240, 1425}, {257, 160, 171}, {691, 440, 437}, {1045, 680, 627}, {301, 200, 171}, {177, 120, 95}, {2141, 1480, 1083}, {1079, 760, 513}, {725, 520, 323}, {137, 100, 57}, {2209, 1640, 855}, {53, 40, 19}, {2243, 1720, 741}, {565, 440, 171}, {759, 600, 209}, {1147, 920, 285}, {2311, 1880, 513}, {97, 80, 19}, {335, 280, 57}, {1181, 1000, 171}, {793, 680, 95}, {599, 520, 57}, {2413, 2120, 171}, {405, 360, 19}, {2447, 2200, 57}, {11, 10, 0}, {158, 151, 3}, {178, 179, 7}, {1030, 1091, 63}, {248, 277, 21}, {318, 375, 35}, {458, 571, 63}, {878, 1159, 147}, {5, 7, 1}, {172, 181, 37}, {97, 76, 22}, {72, 41, 17}, {119, 47, 29}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {65, 18, 17}, {95, 29, 26}, {185, 62, 53}, {30, 11, 9}, {35, 14, 11}, {85, 37, 28}, {55, 26, 19}, {80, 41, 29}, {155, 86, 59}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {305, 176, 119}, {155, 86, 59}, {105, 56, 39}, {80, 41, 29}, {65, 32, 23}, {55, 26, 19}, {335, 152, 113}, {85, 37, 28}, {115, 48, 37}, {35, 14, 11}, {355, 136, 109}, {30, 11, 9}, {365, 128, 107}, {185, 62, 53}, {25, 8, 7}, {95, 29, 26}, {385, 112, 103}, {65, 18, 17}, {395, 104, 101}, {4, 1, 1} }; pipi_image_t *pipi_dither_ostromoukhov(pipi_image_t *img, pipi_scan_t scan) { pipi_image_t *dst; pipi_pixels_t *dstp; float *dstdata; int x, y, w, h; w = img->w; h = img->h; dst = pipi_copy(img); dstp = pipi_get_pixels(dst, PIPI_PIXELS_Y_F32); dstdata = (float *)dstp->pixels; for(y = 0; y < h; y++) { int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE); for(x = 0; x < w; x++) { float p, q, e; int x2, s, i; x2 = reverse ? w - 1 - x : x; s = reverse ? -1 : 1; p = dstdata[y * w + x2]; q = p < 0.5 ? 0. : 1.; dstdata[y * w + x2] = q; e = p - q; i = p * 255.9999; if(i > 127) i = 255 - i; if(i < 0) i = 0; /* XXX: no "else" here */ e /= table[i][0] + table[i][1] + table[i][2]; if(x < w - 1) dstdata[y * w + x2 + s] += e * table[i][0]; if(y < h - 1) { if(x > 0) dstdata[(y + 1) * w + x2 - s] += e * table[i][1]; dstdata[(y + 1) * w + x2] += e * table[i][2]; } } } return dst; }