1 files changed, 142 insertions, 0 deletions
diff --git a/converter/other/pamtohdiff.c b/converter/other/pamtohdiff.c
new file mode 100644
index 00000000..0e1ff00f
--- /dev/null
+++ b/converter/other/pamtohdiff.c
@@ -0,0 +1,142 @@
+/******************************************************************************
+                                 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);
+}
+