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#include "ppm.h"
#include "mallocvar.h"
/*
* Yep, it's a very simple algorithm, but it was something I wanted to have
* available.
*/
struct colorToGrayEntry {
pixel color;
gray gray;
int frequency;
};
/*
* BUG: This number was chosen pretty arbitrarily. The program is * probably
* only useful for a very small numbers of colors - and that's * not only
* because of the O(n) search that's used. The idea lends * itself primarily
* to low color (read: simple, machine generated) images.
*/
#define MAXCOLORS 255
static gray
newGrayValue(pixel *pix, struct colorToGrayEntry *colorToGrayMap, int colors) {
int color;
/*
* Allowing this to be O(n), since the program is intended for small
* n. Later, perhaps sort by color (r, then g, then b) and bsearch.
*/
for (color = 0; color < colors; color++) {
if (PPM_EQUAL(*pix, colorToGrayMap[color].color))
return colorToGrayMap[color].gray;
}
pm_error("This should never happen - contact the maintainer");
return (-1);
}
#ifndef LITERAL_FN_DEF_MATCH
static qsort_comparison_fn cmpColorToGrayEntryByIntensity;
#endif
static int
cmpColorToGrayEntryByIntensity(const void * const a,
const void * const b) {
const struct colorToGrayEntry * const entry1P = a;
const struct colorToGrayEntry * const entry2P = b;
return entry1P->gray - entry2P->gray;
}
#ifndef LITERAL_FN_DEF_MATCH
static qsort_comparison_fn cmpColorToGrayEntryByFrequency;
#endif
static int
cmpColorToGrayEntryByFrequency(const void * const a,
const void * const b) {
const struct colorToGrayEntry * const entry1P = a;
const struct colorToGrayEntry * const entry2P = b;
return entry1P->frequency - entry2P->frequency;
}
int
main(int argc, char *argv[]) {
FILE *ifp;
int col, cols, row, rows, color, colors, argn;
int frequency;
pixval maxval;
pixel **pixels;
pixel *pP;
colorhist_vector hist;
gray *grayrow;
gray *gP;
struct colorToGrayEntry *colorToGrayMap;
ppm_init(&argc, argv);
argn = 1;
/* Default is to sort colors by intensity */
frequency = 0;
while (argn < argc && argv[argn][0] == '-' && argv[argn][1] != '\0') {
if (pm_keymatch(argv[argn], "-frequency", 2))
frequency = 1;
else if (pm_keymatch(argv[argn], "-intensity", 2))
frequency = 0;
else
pm_usage( "[-frequency|-intensity] [ppmfile]" );
++argn;
}
if (argn < argc) {
ifp = pm_openr(argv[argn]);
++argn;
} else
ifp = stdin;
pixels = ppm_readppm(ifp, &cols, &rows, &maxval);
pm_close(ifp);
/* all done with the input file - it's entirely in memory */
/*
* Compute a histogram of the colors in the input. This is good for
* both frequency, and indirectly the intensity, of a color.
*/
hist = ppm_computecolorhist(pixels, cols, rows, MAXCOLORS, &colors);
if (hist == (colorhist_vector) 0)
/*
* BUG: This perhaps should use an exponential backoff, in
* the number of colors, until success - cf pnmcolormap's
* approach. The results are then more what's expected, but
* not necessarily very useful.
*/
pm_error("Too many colors - Try reducing with pnmquant");
/* copy the colors into another structure for sorting */
MALLOCARRAY(colorToGrayMap, colors);
for (color = 0; color < colors; color++) {
colorToGrayMap[color].color = hist[color].color;
colorToGrayMap[color].frequency = hist[color].value;
/*
* This next is derivable, of course, but it's far faster to
* store it precomputed. This can be skipped, when sorting
* by frequency - but again, for a small number of colors
* it's a small matter.
*/
colorToGrayMap[color].gray = ppm_luminosity(hist[color].color);
}
/*
* sort by intensity - sorting by frequency (in the histogram) is
* worth considering as a future addition.
*/
if (frequency)
qsort(colorToGrayMap, colors, sizeof(struct colorToGrayEntry),
&cmpColorToGrayEntryByFrequency);
else
qsort(colorToGrayMap, colors, sizeof(struct colorToGrayEntry),
&cmpColorToGrayEntryByIntensity);
/*
* create mapping between the n colors in input, to n evenly spaced
* grayscale intensities. This is done by overwriting the neatly
* formed gray values corresponding to the input-colors, with a new
* set of evenly spaced gray values. Since maxval can be changed on
* a lark, we just use gray levels 0..colors-1, and adjust maxval
* accordingly
*/
maxval = colors - 1;
for (color = 0; color < colors; color++)
colorToGrayMap[color].gray = color;
/* write pgm file, mapping colors to intensities */
pgm_writepgminit(stdout, cols, rows, maxval, 0);
grayrow = pgm_allocrow(cols);
for (row = 0; row < rows; row++) {
for (col = 0, pP = pixels[row], gP = grayrow; col < cols;
col++, pP++, gP++)
*gP = newGrayValue(pP, colorToGrayMap, colors);
pgm_writepgmrow(stdout, grayrow, cols, maxval, 0);
}
pm_close(stdout);
exit(0);
}
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