source: libpipi/trunk/pipi/dither/ostromoukhov.c

Last change on this file was 3342, checked in by Sam Hocevar, 11 years ago

Change _C pixel format suffixes into _U8 for more clarity.

File size: 4.3 KB
Line 
1/*
2 *  libpipi       Pathetic image processing interface library
3 *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
4 *                All Rights Reserved
5 *
6 *  $Id$
7 *
8 *  This library is free software. It comes without any warranty, to
9 *  the extent permitted by applicable law. You can redistribute it
10 *  and/or modify it under the terms of the Do What The Fuck You Want
11 *  To Public License, Version 2, as published by Sam Hocevar. See
12 *  http://sam.zoy.org/wtfpl/COPYING for more details.
13 */
14
15/*
16 * ostromoukhov.c: Ostromoukhov dithering functions
17 *
18 * This module implements Ostromoukhov's simple error diffusion algorithm,
19 * as introduced in the paper "A Simple and Efficient Error-Diffusion
20 * Algorithm", Proceedings of SIGGRAPH 2001, in ACM Computer Graphics,
21 * Annual Conference Series, pp. 567--572, 2001.
22 *
23 * TODO: the table is actually a piecewise linear function, so it should
24 * be easy to change it into something that works perfectly with floats.
25 */
26
27#include "config.h"
28
29#include "pipi.h"
30#include "pipi_internals.h"
31
32static int const table[][3] =
33{
34     {13, 0, 5}, {13, 0, 5}, {21, 0, 10}, {7, 0, 4},
35     {8, 0, 5}, {47, 3, 28}, {23, 3, 13}, {15, 3, 8},
36     {22, 6, 11}, {43, 15, 20}, {7, 3, 3}, {501, 224, 211},
37     {249, 116, 103}, {165, 80, 67}, {123, 62, 49}, {489, 256, 191},
38     {81, 44, 31}, {483, 272, 181}, {60, 35, 22}, {53, 32, 19},
39     {237, 148, 83}, {471, 304, 161}, {3, 2, 1}, {481, 314, 185},
40     {354, 226, 155}, {1389, 866, 685}, {227, 138, 125}, {267, 158, 163},
41     {327, 188, 220}, {61, 34, 45}, {627, 338, 505}, {1227, 638, 1075},
42     {20, 10, 19}, {1937, 1000, 1767}, {977, 520, 855}, {657, 360, 551},
43     {71, 40, 57}, {2005, 1160, 1539}, {337, 200, 247}, {2039, 1240, 1425},
44     {257, 160, 171}, {691, 440, 437}, {1045, 680, 627}, {301, 200, 171},
45     {177, 120, 95}, {2141, 1480, 1083}, {1079, 760, 513}, {725, 520, 323},
46     {137, 100, 57}, {2209, 1640, 855}, {53, 40, 19}, {2243, 1720, 741},
47     {565, 440, 171}, {759, 600, 209}, {1147, 920, 285}, {2311, 1880, 513},
48     {97, 80, 19}, {335, 280, 57}, {1181, 1000, 171}, {793, 680, 95},
49     {599, 520, 57}, {2413, 2120, 171}, {405, 360, 19}, {2447, 2200, 57},
50     {11, 10, 0}, {158, 151, 3}, {178, 179, 7}, {1030, 1091, 63},
51     {248, 277, 21}, {318, 375, 35}, {458, 571, 63}, {878, 1159, 147},
52     {5, 7, 1}, {172, 181, 37}, {97, 76, 22}, {72, 41, 17},
53     {119, 47, 29}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1},
54     {4, 1, 1}, {4, 1, 1}, {4, 1, 1}, {4, 1, 1},
55     {4, 1, 1}, {4, 1, 1}, {65, 18, 17}, {95, 29, 26},
56     {185, 62, 53}, {30, 11, 9}, {35, 14, 11}, {85, 37, 28},
57     {55, 26, 19}, {80, 41, 29}, {155, 86, 59}, {5, 3, 2},
58     {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2},
59     {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2},
60     {5, 3, 2}, {5, 3, 2}, {5, 3, 2}, {5, 3, 2},
61     {305, 176, 119}, {155, 86, 59}, {105, 56, 39}, {80, 41, 29},
62     {65, 32, 23}, {55, 26, 19}, {335, 152, 113}, {85, 37, 28},
63     {115, 48, 37}, {35, 14, 11}, {355, 136, 109}, {30, 11, 9},
64     {365, 128, 107}, {185, 62, 53}, {25, 8, 7}, {95, 29, 26},
65     {385, 112, 103}, {65, 18, 17}, {395, 104, 101}, {4, 1, 1}
66};
67
68pipi_image_t *pipi_dither_ostromoukhov(pipi_image_t *img, pipi_scan_t scan)
69{
70    pipi_image_t *dst;
71    pipi_pixels_t *dstp;
72    float *dstdata;
73    int x, y, w, h;
74
75    w = img->w;
76    h = img->h;
77
78    dst = pipi_copy(img);
79    dstp = pipi_get_pixels(dst, PIPI_PIXELS_Y_F32);
80    dstdata = (float *)dstp->pixels;
81
82    for(y = 0; y < h; y++)
83    {
84        int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE);
85
86        for(x = 0; x < w; x++)
87        {
88            float p, q, e;
89            int x2, s, i;
90
91            x2 = reverse ? w - 1 - x : x;
92            s = reverse ? -1 : 1;
93
94            p = dstdata[y * w + x2];
95            q = p < 0.5 ? 0. : 1.;
96            dstdata[y * w + x2] = q;
97
98            e = p - q;
99            i = p * 255.9999;
100            if(i > 127) i = 255 - i;
101            if(i < 0) i = 0; /* XXX: no "else" here */
102            e /= table[i][0] + table[i][1] + table[i][2];
103
104            if(x < w - 1)
105                dstdata[y * w + x2 + s] += e * table[i][0];
106            if(y < h - 1)
107            {
108                if(x > 0)
109                    dstdata[(y + 1) * w + x2 - s] += e * table[i][1];
110                dstdata[(y + 1) * w + x2] += e * table[i][2];
111            }
112        }
113    }
114
115    return dst;
116}
117
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