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/******************************************************************************
pamtohdiff
*******************************************************************************
This program creates a PAM output which a horizontal difference image of
the input PAM. The samples in each row are a number to be added to to
the previous output row to create the next output row (and the first
output row is simply the same as the input row).
Because these samples must be positive and negative and PAM samples are
unsigned, we bias each PAM sample by the input maxval and make the output
maxval twice the input maxval.
By Bryan Henderson, San Jose, CA 2002.04.15.
******************************************************************************/
#include <string.h>
#include <stdio.h>
#include "pam.h"
#include "shhopt.h"
struct cmdlineInfo {
/* All the information the user supplied in the command line,
in a form easy for the program to use.
*/
const char *inputFilespec; /* Filespecs of input files */
unsigned int verbose;
};
static void
parseCommandLine(int argc, char ** argv,
struct cmdlineInfo * const cmdlineP) {
/*----------------------------------------------------------------------------
Note that the file spec array we return is stored in the storage that
was passed to us as the argv array.
-----------------------------------------------------------------------------*/
optEntry *option_def = malloc( 100*sizeof( optEntry ) );
/* Instructions to optParseOptions3 on how to parse our options.
*/
optStruct3 opt;
unsigned int option_def_index;
option_def_index = 0; /* incremented by OPTENTRY */
OPTENT3(0, "verbose", OPT_FLAG, NULL, &cmdlineP->verbose, 0);
opt.opt_table = option_def;
opt.short_allowed = FALSE; /* We have no short (old-fashioned) options */
opt.allowNegNum = FALSE; /* We have no parms that are negative numbers */
optParseOptions3( &argc, argv, opt, sizeof(opt), 0 );
/* Uses and sets argc, argv, and some of *cmdlineP and others. */
if (argc-1 < 1)
cmdlineP->inputFilespec = "-";
else if (argc-1 == 1)
cmdlineP->inputFilespec = argv[1];
else
pm_error("Too many arguments.");
}
int
main(int argc, char *argv[]) {
FILE *ifP;
struct cmdlineInfo cmdline;
struct pam inpam, outpam;
unsigned int row;
tuple * inrow;
tuple * outrow;
tuple * prevrow;
pnm_init( &argc, argv );
parseCommandLine(argc, argv, &cmdline);
ifP = pm_openr(cmdline.inputFilespec);
pnm_readpaminit(ifP, &inpam, PAM_STRUCT_SIZE(tuple_type));
outpam = inpam;
outpam.file = stdout;
outpam.format = PAM_FORMAT;
strcpy(outpam.tuple_type, "hdiff");
pnm_writepaminit(&outpam);
inrow = pnm_allocpamrow(&inpam);
outrow = pnm_allocpamrow(&outpam);
prevrow = pnm_allocpamrow(&inpam);
pnm_setpamrow(&inpam, prevrow, 0);
/* All arithmetic in this operation and in the reverse operation
(to recover the image) is done modulus the maxval+1 (the hdiff
PAM and the image have the same maxval) in order to produce
legal PAM samples (which must be in the range 0..maxval). This
might seem to throw away information, but it doesn't. Example:
maxval is 99. Intensity goes from 90 in Row 0 to 10 in Row 1.
The difference is -80. -80 mod 100 is 20, so 20 goes in the
hdiff output. On reconstructing the image, the interpreter
knows the "20" can't be +20, because that would create the
sample 90 + 20 = 110, and violate maxval. So it must be -80.
Modulus arithmetic by the interpreter effectively makes that
decision.
*/
/* The bias is just to make it easier to look at the output visually.
If you display the values as intensities, and your differences are
all +/- half of maxval, you can see positive transitions as bright
spots and negative transitions as dark spots.
*/
{
unsigned int const bias = outpam.maxval/2;
for (row = 0; row < inpam.height; ++row) {
unsigned int col;
pnm_readpamrow(&inpam, inrow);
for (col = 0; col < inpam.width; ++col) {
unsigned int plane;
for (plane = 0; plane < inpam.depth; ++plane) {
sample const sampleValue = inrow[col][plane];
int const difference = sampleValue - prevrow[col][plane];
outrow[col][plane] = (difference + bias) % (outpam.maxval+1);
prevrow[col][plane] = sampleValue;
}
}
pnm_writepamrow(&outpam, outrow);
}
}
pnm_freepamrow(prevrow);
pnm_freepamrow(outrow);
pnm_freepamrow(inrow);
exit(0);
}
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