source: libpipi/trunk/pipi/dither/ediff.c @ 2902

Last change on this file since 2902 was 2902, checked in by Sam Hocevar, 11 years ago

Support C99 types on Win32 through the same hacks as in libcaca.

File size: 2.3 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 * ed.c: generic error diffusion functions
17 */
18
19#include "config.h"
20
21#include "pipi.h"
22#include "pipi_internals.h"
23
24/* Perform a generic error diffusion dithering. The first non-zero
25 * element in ker is treated as the current pixel. All other non-zero
26 * elements are the error diffusion coefficients.
27 * Making the matrix generic is not terribly slower: the performance
28 * hit is around 4% for Floyd-Steinberg and 13% for JaJuNi, with the
29 * benefit of a lot less code. */
30pipi_image_t *pipi_dither_ediff(pipi_image_t *img, pipi_image_t *ker,
31                                pipi_scan_t scan)
32{
33    pipi_image_t *dst;
34    pipi_pixels_t *dstp, *kerp;
35    float *dstdata, *kerdata;
36    int x, y, w, h, i, j, kx, kw, kh;
37
38    w = img->w;
39    h = img->h;
40    kw = ker->w;
41    kh = ker->h;
42
43    dst = pipi_copy(img);
44    dstp = pipi_getpixels(dst, PIPI_PIXELS_Y_F);
45    dstdata = (float *)dstp->pixels;
46
47    kerp = pipi_getpixels(ker, PIPI_PIXELS_Y_F);
48    kerdata = (float *)kerp->pixels;
49    for(kx = 0; kx < kw; kx++)
50        if(kerdata[kx] > 0)
51            break;
52
53    for(y = 0; y < h; y++)
54    {
55        int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE);
56
57        for(x = 0; x < w; x++)
58        {
59            float p, q, e;
60            int x2 = reverse ? w - 1 - x : x;
61            int s = reverse ? -1 : 1;
62
63            p = dstdata[y * w + x2];
64            q = p < 0.5 ? 0. : 1.;
65            dstdata[y * w + x2] = q;
66
67            e = (p - q);
68
69            for(j = 0; j < kh && y < h - j; j++)
70                for(i = 0; i < kw; i++)
71                {
72                    if(j == 0 && i <= kx)
73                        continue;
74
75                    if(x + i - kx < 0 || x + i - kx >= w)
76                        continue;
77
78                    dstdata[(y + j) * w + x2 + (i - kx) * s]
79                       += e * kerdata[j * kw + i];
80                }
81        }
82    }
83
84    return dst;
85}
86
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