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pnmhisteq.c
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1996-11-18
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/*
pnmhisteq.c
Equalise histogram for a PGM or PPM file
Options: -gray: modify gray pixels only; leave colours unchanged
-rmap fn: read luminosity map from PGM file fn
-wmap wn: write luminosity map to PGM file fn
-verbose: print histogram and luminosity map
Accepts PGM and PPM as input. PBM input is allowed, but histogram
equalisation does not modify a PBM file.
by John Walker (kelvin@fourmilab.ch) -- March MVM.
WWW home page: http://www.fourmilab.ch/
Copyright (C) 1995 by John Walker
Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, without any conditions or restrictions. This software is
provided "as is" without express or implied warranty.
*/
#include "pnm.h"
/* Prototypes */
static void hsv_rgb ARGS((double h, double s, double v,
double *r, double *g, double *b));
static void rgb_hsv ARGS((double r, double g, double b,
double *h, double *s, double *v));
/* HSV_RGB -- Convert HSV colour specification to RGB intensities.
Hue is specified as a real value from 0 to 360,
Saturation and Intensity as reals from 0 to 1. The
RGB components are returned as reals from 0 to 1. */
static void hsv_rgb(h, s, v, r, g, b)
double h, s, v;
double *r, *g, *b;
{
int i;
double f, p, q, t;
if (s == 0) {
*r = *g = *b = v;
} else {
if (h == 360.0) {
h = 0;
}
h /= 60.0;
i = h;
f = h - i;
p = v * (1.0 - s);
q = v * (1.0 - (s * f));
t = v * (1.0 - (s * (1.0 - f)));
switch (i) {
case 0:
*r = v;
*g = t;
*b = p;
break;
case 1:
*r = q;
*g = v;
*b = p;
break;
case 2:
*r = p;
*g = v;
*b = t;
break;
case 3:
*r = p;
*g = q;
*b = v;
break;
case 4:
*r = t;
*g = p;
*b = v;
break;
case 5:
*r = v;
*g = p;
*b = q;
break;
}
}
}
/* RGB_HSV -- Map R, G, B intensities in the range from 0 to 1 into
Hue, Saturation, and Value: Hue from 0 to 360,
Saturation from 0 to 1, and Value from 0 to 1.
Special case: if Saturation is 0 (it's a grey scale
tone), Hue is undefined and is returned as -1.
This follows Foley & van Dam, section 17.4.4. */
static void rgb_hsv(r, g, b, h, s, v)
double r, g, b;
double *h, *s, *v;
{
double imax = max(r, max(g, b)),
imin = min(r, min(g, b)),
rc, gc, bc;
*v = imax;
if (imax != 0) {
*s = (imax - imin) / imax;
} else {
*s = 0;
}
if (*s == 0) {
*h = -1;
} else {
rc = (imax - r) / (imax - imin);
gc = (imax - g) / (imax - imin);
bc = (imax - b) / (imax - imin);
if (r == imax) {
*h = bc - gc;
} else if (g == imax) {
*h = 2.0 + rc - bc;
} else {
*h = 4.0 + gc - rc;
}
*h *= 60.0;
if (*h < 0.0) {
*h += 360.0;
}
}
}
int main(argc, argv)
int argc;
char *argv[];
{
FILE *ifp;
int argn = 1, i, j, verbose = 0, mono_only = 0;
gray lmin, lmax;
gray **lumamap; /* Luminosity map */
long *lumahist; /* Histogram of luminosity values */
int rows, hist_cols; /* Rows, columns of input image */
xelval maxval; /* Maxval of input image */
int format; /* Format indicator (PBM/PGM/PPM) */
xel** xels; /* Pixel array */
unsigned long pixels = 0, pixsum = 0, maxluma = 0;
double lscale;
xel *grayrow;
pixel *pixrow;
FILE *rmap = NULL, *wmap = NULL;
char *usage = "[-gray] [-verbose] [-rmap pgmfile] [-wmap pgmfile] [pnmfile]";
pnm_init(&argc, argv);
/* Check for flags. */
while (argn < argc && argv[argn][0] == '-' && argv[argn][1] != '\0') {
if (pm_keymatch(argv[argn], "-gray", 1)) {
mono_only = 1;
} else if (pm_keymatch(argv[argn], "-verbose", 1)) {
verbose = 1;
} else if (pm_keymatch(argv[argn], "-rmap", 1)) {
if (rmap != NULL) {
pm_error("already specified an input map");
}
argn++;
if (argn == argc || strcmp(argv[argn], "-") == 0) {
pm_usage(usage);
}
rmap = pm_openr(argv[argn]);
} else if (pm_keymatch(argv[argn], "-wmap", 1)) {
if (wmap != NULL) {
pm_error("already specified an output map");
}
argn++;
if (argn == argc) {
pm_usage(usage);
}
wmap = pm_openw(argv[argn]);
} else {
pm_usage(usage);
}
argn++;
}
if (--argc > argn) {
pm_usage(usage);
} else if (argc == argn) {
ifp = pm_openr(argv[argn]);
} else {
ifp = stdin;
}
xels = pnm_readpnm(ifp, &hist_cols, &rows, &maxval, &format);
pm_close(ifp);
/* Allocate histogram and luminosity map arrays. If the
user has specified an input map file, read it in at
this point. */
lumahist = (long *) pm_allocrow(maxval + 1, sizeof(long));
bzero((char *) lumahist, (maxval + 1) * sizeof(long));
if (rmap == NULL) {
lumamap = pgm_allocarray(maxval + 1, 1);
} else {
int rmcols, rmrows;
gray rmmaxv;
lumamap = pgm_readpgm(rmap, &rmcols, &rmrows, &rmmaxv);
if (rmmaxv != maxval) {
pm_error("maxval in map file (%d) different from input (%d)",
rmmaxv, maxval);
}
if (rmrows != 1 || rmcols != rmmaxv) {
pm_error("map size (%d by %d) wrong; must be (%d by 1)",
rmcols, rmrows, maxval);
}
}
/* Scan the image and build the luminosity histogram. If
the input is a PPM, we calculate the luminosity of each
pixel from its RGB components. */
lmin = maxval;
lmax = 0;
if (PNM_FORMAT_TYPE(format) == PGM_TYPE ||
PNM_FORMAT_TYPE(format) == PBM_TYPE) {
/* Compute intensity histogram */
pixels = ((unsigned long) rows) * ((unsigned long) hist_cols);
for (i = 0; i < rows; i++) {
xel *grayrow = xels[i];
for (j = 0; j < hist_cols; j++) {
gray l = PNM_GET1(grayrow[j]);
lmin = min(lmin, l);
lmax = max(lmax, l);
lumahist[l]++;
}
}
} else if (PNM_FORMAT_TYPE(format) == PPM_TYPE) {
for (i = 0; i < rows; i++) {
pixel *pixrow = (pixel *) xels[i];
for (j = 0; j < hist_cols; j++) {
if (!mono_only ||
((PPM_GETR(pixrow[j]) == PPM_GETG(pixrow[j])) &&
(PPM_GETR(pixrow[j]) == PPM_GETB(pixrow[j])))) {
gray l = (gray) PPM_LUMIN(pixrow[j]);
lmin = min(lmin, l);
lmax = max(lmax, l);
lumahist[l]++;
pixels++;
}
}
}
} else {
pm_error("unknown input format");
}
/* The PGM and PPM branches rejoin here to calculate the
luminosity mapping table which gives the histogram-equalised
luminosity for each original luminosity. */
/* Calculate initial histogram equalisation curve. */
for (i = 0; i <= (int) maxval; i++) {
/* Yick. If PGM_BIGGRAYS is defined (I thought they were little
guys, about four foot, with funny eyes...) the following
calculation can overflow a 32 bit long. So, we do it in
floating point. Since this happens only maxval times, the
inefficiency is trivial compared to the every-pixel code above
and below. */
lumamap[0][i] = (gray) (((((double) pixsum * maxval)) / pixels) + 0.5);
if (lumahist[i] > 0) {
maxluma = i;
}
pixsum += lumahist[i];
}
/* Normalise so that the brightest pixels are set to
maxval. */
lscale = ((double) maxval) / ((lumahist[maxluma] > 0) ?
((double) lumamap[0][maxluma]) : ((double) maxval));
for (i = 0; i <= (int) maxval; i++) {
lumamap[0][i] = (gray)
min(((long) maxval), ((long) (lumamap[0][i] * lscale + 0.5)));
}
/* If requested, print the luminosity map and original histogram. */
if (verbose) {
fprintf(stderr,
" Luminosity map Number of\n Original New Pixels\n");
for (i = 0; i <= (int) maxval; i++) {
if (lumahist[i] > 0) {
fprintf(stderr,"%6d -> %6d %8d\n", i,
lumamap[0][i], lumahist[i]);
}
}
}
switch (PNM_FORMAT_TYPE(format)) {
case PBM_TYPE:
case PPM_TYPE:
for (i = 0; i < rows; i++) {
pixrow = (pixel *) xels[i];
for (j = 0; j < hist_cols; j++) {
if (!mono_only ||
((PPM_GETR(pixrow[j]) == PPM_GETG(pixrow[j])) &&
(PPM_GETR(pixrow[j]) == PPM_GETB(pixrow[j])))) {
double r, g, b, h, s, v;
int iv;
r = (double) PPM_GETR(pixrow[j]) / ((double) maxval);
g = (double) PPM_GETG(pixrow[j]) / ((double) maxval);
b = (double) PPM_GETB(pixrow[j]) / ((double) maxval);
rgb_hsv(r, g, b, &h, &s, &v);
iv = (int) ((v * maxval) + 0.5);
if (iv > ((int) maxval)) {
iv = maxval;
}
v = ((double) lumamap[0][iv]) / ((double) maxval);
if (v > 1.0) {
v = 1.0;
}
hsv_rgb(h, s, v, &r, &g, &b);
PPM_ASSIGN(pixrow[j], (int) (r * maxval),
(int) (g * maxval), (int) (b * maxval));
}
}
}
break;
case PGM_TYPE:
for (i = 0; i < rows; i++) {
grayrow = xels[i];
for (j = 0; j < hist_cols; j++) {
PNM_ASSIGN1(grayrow[j], lumamap[0][PNM_GET1(grayrow[j])]);
}
}
break;
}
pnm_writepnm(stdout, xels, hist_cols, rows, maxval, format, 0);
/* If requested, save the map as a PGM file. */
if (wmap != NULL) {
pgm_writepgm(wmap, lumamap, maxval, 1, maxval, 0);
fclose(wmap);
}
return 0;
}