source: libpipi/trunk/pipi/filter/median.c @ 3342

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

Change _C pixel format suffixes into _U8 for more clarity.

File size: 3.9 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 * median.c: median filter functions
17 */
18
19#include "config.h"
20
21#include <stdlib.h>
22#include <stdio.h>
23#include <string.h>
24#include <math.h>
25
26#include "pipi.h"
27#include "pipi_internals.h"
28
29static int cmpint(void const *i1, void const *i2)
30{
31    return *(double const *)i1 < *(double const *)i2;
32}
33
34pipi_image_t *pipi_median(pipi_image_t *src, int radius)
35{
36    return pipi_median_ext(src, radius, radius);
37}
38
39/* FIXME: this is in desperate want of optimisation. Here is what could
40 * be done to improve the performance:
41 *  - prefetch the neighbourhood; most neighbours are the same as the
42 *    previous pixels.
43 *  - use a better sort algorithm; bubble sort is ridiculous
44 *  - even better, use state-of-the art median selection, ie. O(3n), for
45 *    most common combinations (9, 25, 49, 81). */
46pipi_image_t *pipi_median_ext(pipi_image_t *src, int rx, int ry)
47{
48    pipi_image_t *dst;
49    pipi_pixels_t *srcp, *dstp;
50    float *srcdata, *dstdata;
51    double *list;
52    int x, y, w, h, i, j, size, gray;
53
54    w = src->w;
55    h = src->h;
56    size = (2 * rx + 1) * (2 * ry + 1);
57
58    gray = (src->last_modified == PIPI_PIXELS_Y_F32);
59
60    srcp = gray ? pipi_get_pixels(src, PIPI_PIXELS_Y_F32)
61                : pipi_get_pixels(src, PIPI_PIXELS_RGBA_F32);
62    srcdata = (float *)srcp->pixels;
63
64    dst = pipi_new(w, h);
65    dstp = gray ? pipi_get_pixels(dst, PIPI_PIXELS_Y_F32)
66                : pipi_get_pixels(dst, PIPI_PIXELS_RGBA_F32);
67    dstdata = (float *)dstp->pixels;
68
69    list = malloc(size * (gray ? 1 : 4) * sizeof(double));
70
71    for(y = 0; y < h; y++)
72    {
73        for(x = 0; x < w; x++)
74        {
75            double *parser = list;
76
77            /* Make a list of neighbours */
78            for(j = -ry; j <= ry; j++)
79            {
80                int y2 = y + j;
81                if(y2 < 0) y2 = h - 1 - ((-y2 - 1) % h);
82                else if(y2 > 0) y2 = y2 % h;
83
84                for(i = -rx; i <= rx; i++)
85                {
86                    int x2 = x + i;
87                    if(x2 < 0) x2 = w - 1 - ((-x2 - 1) % w);
88                    else if(x2 > 0) x2 = x2 % w;
89
90                    if(gray)
91                    {
92                        *parser++ = srcdata[y2 * w + x2];
93                    }
94                    else
95                    {
96                        parser[0] = srcdata[4 * (y2 * w + x2)];
97                        parser[size * 1] = srcdata[4 * (y2 * w + x2) + 1];
98                        parser[size * 2] = srcdata[4 * (y2 * w + x2) + 2];
99                        parser[size * 3] = srcdata[4 * (y2 * w + x2) + 3];
100                        parser++;
101                    }
102                }
103            }
104
105            /* Sort the list */
106            qsort(list, size, sizeof(double), cmpint);
107            if(!gray)
108            {
109                qsort(list + size, size, sizeof(double), cmpint);
110                qsort(list + 2 * size, size, sizeof(double), cmpint);
111                qsort(list + 3 * size, size, sizeof(double), cmpint);
112            }
113
114            /* Store the median value */
115            if(gray)
116            {
117                dstdata[y * w + x] = list[size / 2];
118            }
119            else
120            {
121                dstdata[4 * (y * w + x)] = list[size / 2];
122                dstdata[4 * (y * w + x) + 1] = list[size / 2 + size * 1];
123                dstdata[4 * (y * w + x) + 2] = list[size / 2 + size * 2];
124                dstdata[4 * (y * w + x) + 3] = list[size / 2 + size * 3];
125            }
126        }
127    }
128
129    return dst;
130}
131
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