/*
** pnmtopng.c -
** read a portable anymap and produce a Portable Network Graphics file
**
** derived from pnmtorast.c (c) 1990,1991 by Jef Poskanzer and some
** parts derived from ppmtogif.c by Marcel Wijkstra <wijkstra@fwi.uva.nl>
**
** Copyright (C) 1995-1998 by Alexander Lehmann <alex@hal.rhein-main.de>
**                        and Willem van Schaik <willem@schaik.com>
** Copyright (C) 1999,2001 by Greg Roelofs <newt@pobox.com>
**
** Permission to use, copy, modify, and distribute this software and its
** documentation for any purpose and without fee is hereby granted, provided
** that the above copyright notice appear in all copies and that both that
** copyright notice and this permission notice appear in supporting
** documentation.  This software is provided "as is" without express or
** implied warranty.
*/

/* A performance note: This program reads one row at a time because
   the whole image won't fit in memory always.  When you realize that
   in a Netpbm xel array a one bit pixel can take 96 bits of memory,
   it's easy to see that an ordinary fax could deplete your virtual
   memory and even if it didn't, it might deplete your real memory and
   iterating through the array would cause thrashing.  This program
   iterates through the image multiple times.  

   So instead, we read the image into memory one row at a time, into a
   single row buffer.  We use Netpbm's pm_openr_seekable() facility to
   access the file.  That facility copies the file into a temporary
   file if it isn't seekable, so we always end up with a file that we
   can rewind and reread multiple times.

   This shouldn't cause I/O delays because the entire image ought to fit
   in the system's I/O cache (remember that the file is a lot smaller than
   the xel array you'd get by doing a pnm_readpnm() of it).

   However, it does introduce some delay because of all the system calls 
   required to read the file.  A future enhancement might read the entire
   file into an xel array in some cases, and read one row at a time in 
   others, depending on the needs of the particular use.

   We do still read the entire alpha mask (if there is one) into a
   'gray' array, rather than access it one row at a time.  

   Before May 2001, we did in fact read the whole image into an xel array,
   and we got complaints.  Before April 2000, it wasn't as big a problem
   because xels were only 24 bits.  Now they're 96.
*/
   
#define GRR_GRAY_PALETTE_FIX

#ifndef PNMTOPNG_WARNING_LEVEL
#  define PNMTOPNG_WARNING_LEVEL 0   /* use 0 for backward compatibility, */
#endif                               /*  2 for warnings (1 == error) */

#include <string.h>	/* strcat() */
#include <limits.h>
#include <png.h>	/* includes zlib.h and setjmp.h */
#define VERSION "2.37.6 (21 July 2001) +netpbm"
#include "pnm.h"
#include "pngtxt.h"
#include "mallocvar.h"

typedef struct cahitem {
    xel color;
    gray alpha;
    int value;
    struct cahitem * next;
} cahitem;

typedef cahitem ** coloralphahash_table;

typedef struct _jmpbuf_wrapper {
  jmp_buf jmpbuf;
} jmpbuf_wrapper;

/* GRR 19991205:  this is used as a test for pre-1999 versions of netpbm and
 *   pbmplus vs. 1999 or later (in which pm_close was split into two) 
 */
#ifdef PBMPLUS_RAWBITS
#  define pm_closer pm_close
#  define pm_closew pm_close
#endif

#ifndef TRUE
#  define TRUE 1
#endif
#ifndef FALSE
#  define FALSE 0
#endif
#ifndef NONE
#  define NONE 0
#endif
#define MAXCOLORS 256

/* PALETTEMAXVAL is the maxval used in a PNG palette */
#define PALETTEMAXVAL 255

#define PALETTEOPAQUE 255
#define PALETTETRANSPARENT 0

/* function prototypes */
#ifdef __STDC__
static void pnmtopng_error_handler (png_structp png_ptr, png_const_charp msg);
int main (int argc, char *argv[]);
#endif

static int verbose = FALSE;
static int interlace = FALSE;
static int downscale = FALSE;
static int transparent = -1;
static char *transstring;
static bool alpha = FALSE;
static char *alpha_file;
static int background = -1;
static char *backstring;
static float gamma = -1.0;
static int hist = FALSE;
static float chroma_wx = -1.0;
static float chroma_wy = -1.0;
static float chroma_rx = -1.0;
static float chroma_ry = -1.0;
static float chroma_gx = -1.0;
static float chroma_gy = -1.0;
static float chroma_bx = -1.0;
static float chroma_by = -1.0;
static int phys_x = -1.0;
static int phys_y = -1.0;
static int phys_unit = -1.0;
static int text = FALSE;
static int ztxt = FALSE;
static char *text_file;
static int mtime = FALSE;
static char *date_string;
static char *time_string;
static struct tm time_struct;
static int filter = -1;
static int compression = -1;
static int force = FALSE;
static jmpbuf_wrapper pnmtopng_jmpbuf_struct;
static int errorlevel;



static png_color_16
xelToPngColor_16(xel const input, 
                 xelval const maxval, 
                 xelval const pngMaxval) {
    png_color_16 retval;

    xel scaled;
    
    PPM_DEPTH(scaled, input, maxval, pngMaxval);

    retval.red   = PPM_GETR(scaled);
    retval.green = PPM_GETG(scaled);
    retval.blue  = PPM_GETB(scaled);
    retval.gray  = PNM_GET1(scaled);

    return retval;
}



static void
closestColorInPalette(pixel          const targetColor, 
                      pixel                palette_pnm[],
                      unsigned int   const paletteSize,
                      unsigned int * const bestIndexP,
                      unsigned int * const bestMatchP) {
    
    unsigned int paletteIndex;
    unsigned int bestIndex;
    unsigned int bestMatch;

    bestMatch = UINT_MAX;
    for (paletteIndex = 0; paletteIndex < paletteSize; ++paletteIndex) {
        pixel const thisColor = palette_pnm[paletteIndex];

        unsigned int match = 
            SQR(PPM_GETR(thisColor) - PPM_GETR(targetColor)) +
            SQR(PPM_GETG(thisColor) - PPM_GETG(targetColor)) +
            SQR(PPM_GETB(thisColor) - PPM_GETB(targetColor));

        if (match < bestMatch) {
            bestMatch = match;
            bestIndex = paletteIndex;
        }
    }
    if (bestIndexP != NULL)
        *bestIndexP = bestIndex;
    if (bestMatchP != NULL)
        *bestMatchP = bestMatch;
}



/* We really ought to make this hash function actually depend upon
   the "a" argument; we just don't know a decent prime number off-hand.
*/
#define HASH_SIZE 20023
#define hashpixelalpha(p,a) ((((long) PPM_GETR(p) * 33023 + \
                               (long) PPM_GETG(p) * 30013 + \
                               (long) PPM_GETB(p) * 27011 ) \
                              & 0x7fffffff ) % HASH_SIZE )

static coloralphahash_table
alloccoloralphahash(void)  {
    coloralphahash_table caht;
    int i;

    MALLOCARRAY(caht,HASH_SIZE);
    if (caht == NULL)
        pm_error( "out of memory allocating hash table" );

    for (i = 0; i < HASH_SIZE; ++i)
        caht[i] = NULL;

    return caht;
}


static void
freecoloralphahash(coloralphahash_table const caht) {
    int i;

    for (i = 0; i < HASH_SIZE; ++i) {
        cahitem * p;
        cahitem * next;
        for (p = caht[i]; p; p = next) {
            next = p->next;
            free(p);
        }
    }
    free(caht);
}



static void
addtocoloralphahash(coloralphahash_table const caht,
                    pixel *              const colorP,
                    gray *               const alphaP,
                    int                  const value) {

    int hash;
    cahitem * itemP;

    MALLOCVAR(itemP);
    if (itemP == NULL)
        pm_error("Out of memory building hash table");
    hash = hashpixelalpha(*colorP, *alphaP);
    itemP->color = *colorP;
    itemP->alpha = *alphaP;
    itemP->value = value;
    itemP->next = caht[hash];
    caht[hash] = itemP;
}



static int
lookupColorAlpha(coloralphahash_table const caht,
                 pixel const * const colorP,
                 gray * const alphaP) {

    int hash;
    cahitem * p;

    hash = hashpixelalpha(*colorP, *alphaP);
    for (p = caht[hash]; p; p = p->next)
        if (PPM_EQUAL(p->color, *colorP) && p->alpha == *alphaP)
            return p->value;

    return -1;
}



#ifdef __STDC__
static void pnmtopng_error_handler (png_structp png_ptr, png_const_charp msg)
#else
static void pnmtopng_error_handler (png_ptr, msg)
png_structp png_ptr;
png_const_charp msg;
#endif
{
  jmpbuf_wrapper  *jmpbuf_ptr;

  /* this function, aside from the extra step of retrieving the "error
   * pointer" (below) and the fact that it exists within the application
   * rather than within libpng, is essentially identical to libpng's
   * default error handler.  The second point is critical:  since both
   * setjmp() and longjmp() are called from the same code, they are
   * guaranteed to have compatible notions of how big a jmp_buf is,
   * regardless of whether _BSD_SOURCE or anything else has (or has not)
   * been defined. */

  fprintf(stderr, "pnmtopng:  fatal libpng error: %s\n", msg);
  fflush(stderr);

  jmpbuf_ptr = png_get_error_ptr(png_ptr);
  if (jmpbuf_ptr == NULL) {         /* we are completely hosed now */
    fprintf(stderr,
      "pnmtopng:  EXTREMELY fatal error: jmpbuf unrecoverable; terminating.\n");
    fflush(stderr);
    exit(99);
  }

  longjmp(jmpbuf_ptr->jmpbuf, 1);
}


/* The following variables belong to getChv() and freeChv() */
static bool getChv_computed = FALSE;
static colorhist_vector getChv_chv;
static int getChv_colors;



static void
getChv(FILE *             const ifP, 
       pm_filepos         const imagepos,
       int                const cols, 
       int                const rows, 
       xelval             const maxval,
       int                const format, 
       int                const maxColors, 
       colorhist_vector * const chvP,
       int *              const colorsP) {
/*----------------------------------------------------------------------------
   Return a list of all the colors in a libpnm image and the number of
   times they occur.  The image is in the seekable file 'ifP', whose
   raster starts at position 'imagepos' of the file.  The image's properties
   are 'cols', 'rows', 'maxval', and 'format'.

   Return the number of colors as *colorsP.  Return the details of the 
   colors in newly malloc'ed storage, and its address as *chvP.  If
   there are more than 'maxColors' colors, though, just return NULL as
   *chvP and leave *colorsP undefined.

   Don't spend the time to read the file if this subroutine has been called
   before.  In that case, just assume the inputs are all the same and return
   the previously computed information.

   *chvP is in static program storage.
-----------------------------------------------------------------------------*/
    if (!getChv_computed) {
        if (verbose) 
            pm_message ("Finding colors in input image...");

        pm_seek2(ifP, &imagepos, sizeof(imagepos));
        getChv_chv = ppm_computecolorhist2(ifP, cols, rows, maxval, format, 
                                           MAXCOLORS, &getChv_colors);
        
        if (getChv_chv)
            pm_message ("%d colors found", getChv_colors);

        getChv_computed = TRUE;
    }
    *chvP = getChv_chv;
    *colorsP = getChv_colors;
}



static void freeChv(void) {

    if (getChv_computed)
        if (getChv_chv)
            ppm_freecolorhist(getChv_chv);

    getChv_computed = FALSE;
}



static void
meaningful_bits_pgm(FILE *         const ifp, 
                    pm_filepos     const imagepos, 
                    int            const cols,
                    int            const rows,
                    xelval         const maxval,
                    int            const format,
                    unsigned int * const retvalP) {
/*----------------------------------------------------------------------------
   In the PGM raster with maxval 'maxval' at file offset 'imagepos'
   in file 'ifp', the samples may be composed of groups of 1, 2, 4, or 8
   bits repeated.  This would be the case if the image were converted
   at some point from a 2 bits-per-pixel image to an 8-bits-per-pixel
   image, for example.

   If this is the case, we find out and find out how small these repeated
   groups of bits are and return the number of bits.
-----------------------------------------------------------------------------*/
    int mayscale;
    int x, y;
    xel * xelrow;

    xelrow = pnm_allocrow(cols);

    *retvalP = pm_maxvaltobits(maxval);

    if (maxval == 65535) {
        mayscale = TRUE;   /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (y = 0 ; y < rows && mayscale ; y++) {
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (x = 0 ; x < cols && mayscale ; x++) {
                xel const p = xelrow[x];
                if ( (PNM_GET1 (p)&0xff)*0x101 != PNM_GET1 (p) )
                    mayscale = FALSE;
            }
        }
        if (mayscale)
            *retvalP = 8;
    }
    if (maxval == 255 || *retvalP == 8) {
        mayscale = TRUE;  /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (y = 0 ; y < rows && mayscale ; y++) {
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (x = 0 ; x < cols && mayscale ; x++) {
                if ((PNM_GET1 (xelrow[x]) & 0xf) * 0x11 
                    != PNM_GET1 (xelrow[x]))
                    mayscale = FALSE;
            }
        }
        if (mayscale)
            *retvalP = 4;
    }

    if (maxval == 15 || *retvalP == 4) {
        mayscale = TRUE;   /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (y = 0 ; y < rows && mayscale ; y++) {
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (x = 0 ; x < cols && mayscale ; x++) {
                if ((PNM_GET1 (xelrow[x])&3) * 0x5 != PNM_GET1 (xelrow[x]))
                    mayscale = FALSE;
            }
        }
        if (mayscale) {
            *retvalP = 2;
        }
    }

    if (maxval == 3 || *retvalP == 2) {
        mayscale = TRUE;   /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (y = 0 ; y < rows && mayscale ; y++) {
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (x = 0 ; x < cols && mayscale ; x++) {
                if ((PNM_GET1 (xelrow[x])&1) * 0x3 != PNM_GET1 (xelrow[x]))
                    mayscale = FALSE;
            }
        }
        if (mayscale) {
            *retvalP = 1;
        }
    }
    pnm_freerow(xelrow);
}


static void
meaningful_bits_ppm(FILE *         const ifp, 
                    pm_filepos     const imagepos, 
                    int            const cols,
                    int            const rows,
                    xelval         const maxval,
                    int            const format,
                    unsigned int * const retvalP) {
/*----------------------------------------------------------------------------
   In the PPM raster with maxval 'maxval' at file offset 'imagepos'
   in file 'ifp', the samples may be composed of groups of 8
   bits repeated twice.  This would be the case if the image were converted
   at some point from a 8 bits-per-pixel image to an 16-bits-per-pixel
   image, for example.

   We return the smallest number of bits we can take from the right of
   a sample without losing information (8 or all).
-----------------------------------------------------------------------------*/
    int mayscale;
    int x, y;
    xel * xelrow;

    xelrow = pnm_allocrow(cols);

    *retvalP = pm_maxvaltobits(maxval);

    if (maxval == 65535) {
        mayscale = TRUE;   /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (y = 0 ; y < rows && mayscale ; y++) {
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (x = 0 ; x < cols && mayscale ; x++) {
                xel const p = xelrow[x];
                if ( (PPM_GETR (p)&0xff)*0x101 != PPM_GETR (p) ||
                     (PPM_GETG (p)&0xff)*0x101 != PPM_GETG (p) ||
                     (PPM_GETB (p)&0xff)*0x101 != PPM_GETB (p) )
                    mayscale = FALSE;
            }
        }
        if (mayscale)
            *retvalP = 8;
    }
    pnm_freerow(xelrow);
}



static void
alpha_trans(FILE *     const ifp, 
            pm_filepos const imagepos, 
            int        const cols, 
            int        const rows, 
            xelval     const maxval, int const format, 
            gray **    const alpha_mask, gray alpha_maxval,
            bool *     const alpha_can_be_transparency_indexP, 
            pixel*     const alpha_transcolorP) {
/*----------------------------------------------------------------------------
  Check if the alpha mask can be represented by a single transparency
  value (i.e. all colors fully opaque except one fully transparent;
  the transparent color may not also occur as fully opaque.
  we have to do this before any scaling occurs, since alpha is only
  possible with 8 and 16-bit.
-----------------------------------------------------------------------------*/
    xel * xelrow;
    bool retval;
        /* Our eventual return value -- alpha mask can be represented by
           a simple transparency index.
        */
    bool found_transparent_pixel;
        /* We found a pixel in the image where the alpha mask says it is
           transparent.
        */
    pixel transcolor;
        /* Color of the transparent pixel mentioned above. */
    int const pnm_type = PNM_FORMAT_TYPE(format);
    
    xelrow = pnm_allocrow(cols);

    {
        int row;
        /* Find a candidate transparent color -- the color of any pixel in the
           image that the alpha mask says should be transparent.
        */
        found_transparent_pixel = FALSE;  /* initial assumption */
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        for (row = 0 ; row < rows && !found_transparent_pixel ; ++row) {
            int col;
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (col = 0 ; col < cols && !found_transparent_pixel; ++col) {
                if (alpha_mask[row][col] == 0) {
                    found_transparent_pixel = TRUE;
                    transcolor = xeltopixel(xelrow[col]);
                }
            }
        }
    }

    if (found_transparent_pixel) {
        int row;
        pm_seek2(ifp, &imagepos, sizeof(imagepos));
        retval = TRUE;  /* initial assumption */
        
        for (row = 0 ; row < rows && retval == TRUE; ++row) {
            int col;
            pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
            for (col = 0 ; col < cols && retval == TRUE; ++col) {
                if (alpha_mask[row][col] == 0) { /* transparent */
                    /* If we have a second transparent color, we're
                       disqualified
                    */
                    if (pnm_type == PPM_TYPE) {
                        if (!PPM_EQUAL (xelrow[col], transcolor))
                            retval = FALSE;
                    } else {
                        if (PNM_GET1 (xelrow[col]) != PNM_GET1 (transcolor))
                            retval = FALSE;
                    }
                } else if (alpha_mask[row][col] != alpha_maxval) {
                    /* Here's an area of the mask that is translucent.  That
                       disqualified us.
                    */
                    retval = FALSE;
                } else 
                    /* Here's an area of the mask that is opaque.  If it's
                       the same color as our candidate transparent color,
                       that disqualifies us.
                    */
                    if (pnm_type == PPM_TYPE) {
                        if (PPM_EQUAL (xelrow[col], transcolor))
                            retval = FALSE;
                    } else {
                        if (PNM_GET1 (xelrow[col]) == PNM_GET1 (transcolor))
                            retval = FALSE;
                    }
            }
        }  
    }
    pnm_freerow(xelrow);

    *alpha_can_be_transparency_indexP = retval;
    *alpha_transcolorP = transcolor;
}



static void
findRedundantBits(FILE * const ifp, 
                  int const imagepos, 
                  int const cols,
                  int const rows,
                  xelval const maxval,
                  int const format,
                  bool const alpha,
                  bool const force,
                  unsigned int * const meaningfulBitsP) {
/*----------------------------------------------------------------------------
   Find out if we can use just a subset of the bits from each input sample.
   Often, people create an image with e.g. 8 bit samples from one that has
   e.g. only 4 bit samples by just repeating the bits.  1011 becomes
   10111011.  We detect this case.  We return as *meaningfulBitsP the
   minimum number of bits, starting from the least significant end, that
   contain original information.
-----------------------------------------------------------------------------*/
  if (!alpha && PNM_FORMAT_TYPE(format) == PGM_TYPE && !force) 
      meaningful_bits_pgm(ifp, imagepos, cols, rows, maxval, format,
                          meaningfulBitsP);
  else if (PNM_FORMAT_TYPE(format) == PPM_TYPE && !force)
      meaningful_bits_ppm(ifp, imagepos, cols, rows, maxval, format,
                          meaningfulBitsP);
  else 
      *meaningfulBitsP = pm_maxvaltobits(maxval);

  if (verbose && *meaningfulBitsP != pm_maxvaltobits(maxval))
      pm_message("Using only %d rightmost bits of input samples.  The "
                 "rest are just copies of those.", *meaningfulBitsP);
}



static void
readOrderedPalette(FILE * const   pfp,
                   xel            ordered_palette[], 
                   unsigned int * const ordered_palette_size_p) {

    xel ** xels;
    int cols, rows;
    xelval maxval;
    int format;
    
    if (verbose)
        pm_message ("reading ordered palette (colormap)...");

    xels = pnm_readpnm (pfp, &cols, &rows, &maxval, &format);
    
    if (PNM_FORMAT_TYPE(format) != PPM_TYPE) 
        pm_error("ordered palette must be a PPM file, not type %d", format);

    *ordered_palette_size_p = rows * cols;
    if (*ordered_palette_size_p > MAXCOLORS) 
        pm_error("ordered-palette image contains %d pixels.  Maximum is %d",
                 *ordered_palette_size_p, MAXCOLORS);
    if (verbose)
      pm_message ("%d colors found", *ordered_palette_size_p);

    {
        int j;
        int row;
        j = 0;  /* initial value */
        for (row = 0; row < rows; ++row) {
            int col;
            for (col = 0; col < cols; ++col) 
                ordered_palette[j++] = xels[row][col];
        }
    }
    pnm_freearray(xels, rows);
}        



static void
compute_nonalpha_palette(colorhist_vector const chv,
                         int              const colors,
                         pixval           const maxval,
                         FILE *           const pfp,
                         pixel                  palette_pnm[],
                         unsigned int *   const paletteSizeP,
                         gray                   trans_pnm[],
                         unsigned int *   const transSizeP) {
/*----------------------------------------------------------------------------
   Compute the palette corresponding to the color set 'chv'
   (consisting of 'colors' distinct colors) assuming a pure-color (no
   transparency) palette.

   If 'php' is non-null, assume it's a PPM file and read the palette
   from that.  Make sure it contains the same colors as the palette
   we computed ourself would have.  Caller supplied the file because he
   wants the colors in a particular order in the palette.
-----------------------------------------------------------------------------*/
    unsigned int colorIndex;
    
    xel ordered_palette[MAXCOLORS];
    unsigned int ordered_palette_size;

    if (pfp) {
        readOrderedPalette(pfp, ordered_palette, &ordered_palette_size);

        if (colors != ordered_palette_size) 
            pm_error("sizes of ordered palette (%d) "
                     "and existing palette (%d) differ",
                     ordered_palette_size, colors);
        
        /* Make sure the ordered palette contains all the colors in
           the image 
        */
        for (colorIndex = 0; colorIndex < colors; colorIndex++) {
            int j;
            bool found;
            
            found = FALSE;
            for (j = 0; j < ordered_palette_size && !found; ++j) {
                if (PNM_EQUAL(ordered_palette[j], chv[colorIndex].color)) 
                    found = TRUE;
            }
            if (!found) 
                pm_error("failed to find color (%d, %d, %d), which is in the "
                         "input image, in the ordered palette",
                         PPM_GETR(chv[colorIndex].color),
                         PPM_GETG(chv[colorIndex].color),
                         PPM_GETB(chv[colorIndex].color));
        }
        /* OK, the ordered palette passes muster as a palette; go ahead
           and return it as the palette.
        */
        for (colorIndex = 0; colorIndex < colors; ++colorIndex)
            palette_pnm[colorIndex] = ordered_palette[colorIndex];
    } else {
        for (colorIndex = 0; colorIndex < colors; ++colorIndex) 
            palette_pnm[colorIndex] = chv[colorIndex].color;
    }
    *paletteSizeP = colors;
    *transSizeP = 0;
}



static void
compute_alpha_palette(FILE *         const ifP, 
                      int            const cols,
                      int            const rows,
                      xelval         const maxval,
                      int            const format,
                      pm_filepos     const imagepos,
                      gray **        const alpha_mask,
                      pixel                palette_pnm[],
                      gray                 trans_pnm[],
                      unsigned int * const paletteSizeP,
                      unsigned int * const transSizeP,
                      bool *         const tooBigP) {
/*----------------------------------------------------------------------------
   Return the palette of color/alpha pairs for the image indicated by
   'ifP', 'cols', 'rows', 'maxval', 'format', and 'imagepos'.
   alpha_mask[] is the Netpbm-style alpha mask for the image.

   Return the palette as the arrays palette_pnm[] and trans_pnm[].
   The ith entry in the palette is the combination of palette[i],
   which defines the color, and trans[i], which defines the
   transparency.

   Return the number of entries in the palette as *paletteSizeP.

   The palette is sorted so that the opaque entries are last, and we return
   *transSizeP as the number of non-opaque entries.

   palette[] and trans[] are allocated by the caller to at least MAXCOLORS
   elements.

   If there are more than MAXCOLORS color/alpha pairs in the image, don't
   return any palette information -- just return *tooBigP == TRUE.
-----------------------------------------------------------------------------*/
    colorhist_vector chv;
    int colors;
    colorhash_table cht;
    int color_index;
    int row;
    xel * xelrow;

    /* The following data structures describe the alpha/color palette.
       The alpha/color palette is the set of all ordered pairs of
       (color,alpha) in the PNG, including the background color.  The
       actual palette is an array with up to MAXCOLORS elements.  Each
       array element contains a color index from the color palette and
       an alpha value.  All the elements with the same color index are
       contiguous.  alphas_first_index[x] is the index in the
       alpha/color palette of the first element that has color index x.
       alphas_of_color_cnt[x] is the number of elements that have color
       index x.  alphas_of_color[x][y] is the yth alpha value that
       appears with color index x (in order of appearance).
       alpha_color_pair_count is the total number of elements, i.e. the
       total number of combinations color and alpha.
    */
    gray *alphas_of_color[MAXCOLORS];
    unsigned int alphas_first_index[MAXCOLORS];
    unsigned int alphas_of_color_cnt[MAXCOLORS];

    getChv(ifP, imagepos, cols, rows, maxval, format, MAXCOLORS, 
           &chv, &colors);
    cht = ppm_colorhisttocolorhash (chv, colors);

    for (color_index = 0 ; color_index < colors + 1 ; ++color_index) {
        MALLOCARRAY(alphas_of_color[color_index], MAXCOLORS);
        if (alphas_of_color[color_index] == NULL)
            pm_error ("out of memory allocating alpha/palette entries");
        alphas_of_color_cnt[color_index] = 0;
    }
 
    pm_seek2(ifP, &imagepos, sizeof(imagepos));

    xelrow = pnm_allocrow(cols);

    for (row = 0 ; row < rows ; ++row) {
        int col;
        pnm_readpnmrow(ifP, xelrow, cols, maxval, format);
        pnm_promoteformatrow(xelrow, cols, maxval, format, maxval, PPM_TYPE);
        for (col = 0 ; col < cols ; ++col) {
            int i;
            int const color = ppm_lookupcolor(cht, &xelrow[col]);
            for (i = 0 ; i < alphas_of_color_cnt[color] ; i++) {
                if (alpha_mask[row][col] == alphas_of_color[color][i])
                    break;
            }
            if (i == alphas_of_color_cnt[color]) {
                alphas_of_color[color][i] = alpha_mask[row][col];
                alphas_of_color_cnt[color]++;
            }
        }
    }
    pnm_freerow(xelrow);

    {
        int i;
        alphas_first_index[0] = 0;
        for (i = 1 ; i < colors ; i++)
            alphas_first_index[i] = alphas_first_index[i-1] +
                alphas_of_color_cnt[i-1];
    }
    *paletteSizeP = 
        alphas_first_index[colors-1] + alphas_of_color_cnt[colors-1];
    if (*paletteSizeP > MAXCOLORS) {
        *tooBigP = TRUE;
    } else {
        int mapping[MAXCOLORS];
            /* Sorting of the alpha/color palette.  mapping[x] is the
               index into the sorted PNG palette of the alpha/color
               pair whose index is x in the unsorted PNG palette.
               This mapping sorts the palette so that opaque entries
               are last.  
            */
        unsigned int bot_idx;
        unsigned int top_idx;
        unsigned int colorIndex;

        *tooBigP = FALSE;

        bot_idx = 0;
        top_idx = alphas_first_index[colors-1] + alphas_of_color_cnt[colors-1] - 1;

        /* remap palette indices so opaque entries are last */
        for (colorIndex = 0;  colorIndex < colors;  ++colorIndex) {
            unsigned int j;
            for (j = 0; j < alphas_of_color_cnt[colorIndex]; ++j) {
                unsigned int const paletteIndex = 
                    alphas_first_index[colorIndex] + j;
                if (alphas_of_color[colorIndex][j] == PALETTEOPAQUE)
                    mapping[paletteIndex] = top_idx--;
                else
                    mapping[paletteIndex] = bot_idx++;
            }
        }
        /* indices should have just crossed paths */
        if (bot_idx != top_idx + 1) {
            pm_error ("internal inconsistency: "
                      "remapped bot_idx = %d, top_idx = %d",
                      bot_idx, top_idx);
        }
        for (colorIndex = 0; colorIndex < colors; ++colorIndex) {
            unsigned int j;
            for (j = 0; j < alphas_of_color_cnt[colorIndex]; ++j) {
                unsigned int const paletteIndex = 
                    alphas_first_index[colorIndex] + j;
                palette_pnm[mapping[paletteIndex]] = chv[colorIndex].color;
                trans_pnm[mapping[paletteIndex]] = 
                    alphas_of_color[colorIndex][j];
            }
        }
        *transSizeP = bot_idx;
    }
    { 
        unsigned int color_index;
        for (color_index = 0; color_index < colors + 1; ++color_index)
            free(alphas_of_color[color_index]);
    }
    ppm_freecolorhash(cht);
} 




static void
makeOneColorTransparentInPalette(xel            const transColor, 
                                 bool           const exact,
                                 pixel                palette_pnm[],
                                 unsigned int   const paletteSize,
                                 gray                 trans_pnm[],
                                 unsigned int * const transSizeP) {
/*----------------------------------------------------------------------------
   Find the color 'transColor' in the color/alpha palette defined by
   palette_pnm[], paletteSize, trans_pnm[] and *transSizeP.  If it's
   not there and exact == TRUE, return without changing anything, but
   issue a warning message.  If it's not there and exact == FALSE,
   just find the closest color.

   Make that entry fully transparent.

   Rearrange the palette so that that entry is first.  (The PNG compressor
   can do a better job when the opaque entries are all last in the 
   color/alpha palette).

   We assume every entry in the palette is opaque upon entry.
-----------------------------------------------------------------------------*/
    unsigned int transparentIndex;
    unsigned int distance;
    
    if (*transSizeP != 0)
        pm_error("Internal error: trying to make a color in the palette "
                 "transparent where there already is one.");

    closestColorInPalette(transColor, palette_pnm, paletteSize, 
                          &transparentIndex, &distance);

    if (distance != 0 && exact) {
        pm_message ("specified transparent color not present in palette; "
                    "ignoring -transparent");
        errorlevel = PNMTOPNG_WARNING_LEVEL;
    } else {        
        /* Swap this with the first entry in the palette */
        pixel tmp;
    
        tmp = palette_pnm[transparentIndex];
        palette_pnm[transparentIndex] = palette_pnm[0];
        palette_pnm[0] = tmp;
        
        /* Make it transparent */
        trans_pnm[0] = PGM_TRANSPARENT;
        *transSizeP = 1;
        if (verbose) {
            pixel const p = palette_pnm[0];
            pm_message("Making all occurences of color (%u, %u, %u) "
                       "transparent.",
                       PPM_GETR(p), PPM_GETG(p), PPM_GETB(p));
        }
    }
}



static void
findOrAddBackgroundInPalette(pixel          const backColor, 
                             pixel                palette_pnm[], 
                             unsigned int * const paletteSizeP,
                             unsigned int * const backgroundIndexP) {
/*----------------------------------------------------------------------------
  Add the background color 'backColor' to the palette, unless
  it's already in there.  If it's not present and there's no room to
  add it, choose a background color that's already in the palette,
  as close to 'backColor' as possible.

  If we add an entry to the palette, make it opaque.  But in searching the 
  existing palette, ignore transparency.

  Note that PNG specs say that transparency of the background is meaningless;
  i.e. a viewer must ignore the transparency of the palette entry when 
  using the background color.
-----------------------------------------------------------------------------*/
    int backgroundIndex;  /* negative means not found */
    unsigned int paletteIndex;

    backgroundIndex = -1;
    for (paletteIndex = 0; 
         paletteIndex < *paletteSizeP; 
         ++paletteIndex) 
        if (PPM_EQUAL(palette_pnm[paletteIndex], backColor))
            backgroundIndex = paletteIndex;

    if (backgroundIndex >= 0) {
        /* The background color is already in the palette. */
        *backgroundIndexP = backgroundIndex;
        if (verbose) {
            pixel const p = palette_pnm[*backgroundIndexP];
            pm_message ("background color (%u, %u, %u) appears in image.",
                        PPM_GETR(p), PPM_GETG(p), PPM_GETB(p));
        }
    } else {
        /* Try to add the background color, opaque, to the palette. */
        if (*paletteSizeP < MAXCOLORS) {
            /* There's room, so just add it to the end of the palette */

            /* Because we're not expanding the transparency palette, this
               entry is not in it, and is thus opaque.
            */
            *backgroundIndexP = (*paletteSizeP)++;
            palette_pnm[*backgroundIndexP] = backColor;
            if (verbose) {
                pixel const p = palette_pnm[*backgroundIndexP];
                pm_message ("added background color (%u, %u, %u) to palette.",
                            PPM_GETR(p), PPM_GETG(p), PPM_GETB(p));
            }
        } else {
            closestColorInPalette(backColor, palette_pnm, *paletteSizeP,
                                  backgroundIndexP, NULL);
            errorlevel = PNMTOPNG_WARNING_LEVEL;
            if (verbose) {
                pixel const p = palette_pnm[*backgroundIndexP];
                pm_message ("no room in palette for background color; "
                            "using closest match (%u, %u, %u) instead",
                            PPM_GETR(p), PPM_GETG(p), PPM_GETB(p));
            }
        }
    }
}



static void 
buildColorLookup(pixel                   palette_pnm[], 
                 unsigned int      const paletteSize,
                 colorhash_table * const chtP) {
/*----------------------------------------------------------------------------
   Create a colorhash_table out of the palette described by
   palette_pnm[] (which has 'paletteSize' entries) so one can look up
   the palette index of a given color.

   Where the same color appears twice in the palette, the lookup table
   finds an arbitrary one of them.  We don't consider transparency of
   palette entries, so if the same color appears in the palette once
   transparent and once opaque, the lookup table finds an arbitrary one
   of those two.
-----------------------------------------------------------------------------*/
    colorhash_table const cht = ppm_alloccolorhash();
    unsigned int paletteIndex;

    for (paletteIndex = 0; paletteIndex < paletteSize; ++paletteIndex) {
        ppm_addtocolorhash(cht, &palette_pnm[paletteIndex], paletteIndex);
    }
    *chtP = cht;
}


static void 
buildColorAlphaLookup(pixel              palette_pnm[], 
                      unsigned int const paletteSize,
                      gray               trans_pnm[], 
                      unsigned int const transSize,
                      gray         const alphaMaxval,
                      coloralphahash_table * const cahtP) {
    
    coloralphahash_table const caht = alloccoloralphahash();

    unsigned int paletteIndex;

    for (paletteIndex = 0; paletteIndex < paletteSize; ++paletteIndex) {
        gray paletteTrans;

        if (paletteIndex < transSize)
            paletteTrans = alphaMaxval;
        else
            paletteTrans = trans_pnm[paletteIndex];


        addtocoloralphahash(caht, &palette_pnm[paletteIndex],
                            &trans_pnm[paletteIndex], paletteIndex);
    }
    *cahtP = caht;
}



static void computeColorMapLookupTable(
    bool                   const colorMapped,
    pixel                        palette_pnm[],
    unsigned int           const palette_size,
    gray                         trans_pnm[],
    unsigned int           const trans_size,
    bool                   const alpha,
    xelval                 const alpha_maxval,
    colorhash_table *      const chtP,
    coloralphahash_table * const cahtP) {
/*----------------------------------------------------------------------------
   Compute applicable lookup tables for the palette index.  If there's no
   alpha mask, this is just a standard Netpbm colorhash_table.  If there's
   an alpha mask, it is the slower Pnmtopng-specific 
   coloralphahash_table.

   If a lookup table is not applicable to the image, return NULL as
   its address.  (If the image is not colormapped, both will be NULL).
-----------------------------------------------------------------------------*/
    if (colorMapped) {
        if (alpha) {
            buildColorAlphaLookup(palette_pnm, palette_size, 
                                  trans_pnm, trans_size, alpha_maxval, cahtP);
            *chtP = NULL;
        } else { 
            buildColorLookup(palette_pnm, palette_size, chtP);
            *cahtP = NULL;
        }
        if (verbose)
            pm_message("PNG palette has %u entries, %u of them non-opaque",
                       palette_size, trans_size);
    } else {
        *chtP = NULL;
        *cahtP = NULL;
    }
}



static void
computePixelWidth(bool           const colorMapped,
                  unsigned int   const palette_size,
                  int            const pnm_type,
                  unsigned int   const pnm_meaningful_bits,
                  bool           const alpha,
                  unsigned int * const bitsPerSampleP,
                  unsigned int * const bitsPerPixelP) {
/*----------------------------------------------------------------------------
   Compute the number of bits per raster sample and per raster pixel:
   *bitsPerSampleP and *bitsPerPixelP.  Note that a raster element may be a
   palette index, or a gray value or color with or without alpha mask.
-----------------------------------------------------------------------------*/
    if (colorMapped) {
        if (palette_size <= 2)
            *bitsPerSampleP = 1;
        else if (palette_size <= 4)
            *bitsPerSampleP = 2;
        else if (palette_size <= 16)
            *bitsPerSampleP = 4;
        else
            *bitsPerSampleP = 8;
        *bitsPerPixelP = *bitsPerSampleP;
        if (verbose)
            pm_message("Writing %d-bit color indexes", *bitsPerSampleP);
    } else {
        if (pnm_type == PPM_TYPE || alpha) {
            /* PNG allows only depths of 8 and 16 for a truecolor image 
               and for a grayscale image with an alpha channel.
          */
            if (pnm_meaningful_bits > 8)
                *bitsPerSampleP = 16;
            else 
                *bitsPerSampleP = 8;
        } else {
            /* A grayscale, non-colormapped, no-alpha PNG may have any 
             bit depth from 1 to 16
          */
            if (pnm_meaningful_bits > 8)
                *bitsPerSampleP = 16;
            else if (pnm_meaningful_bits > 4)
                *bitsPerSampleP = 8;
            else if (pnm_meaningful_bits > 2)
                *bitsPerSampleP = 4;
            else if (pnm_meaningful_bits > 1)
                *bitsPerSampleP = 2;
            else
                *bitsPerSampleP = 1;
        }
        if (alpha) {
            if (pnm_type == PPM_TYPE)
                *bitsPerPixelP = 4 * *bitsPerSampleP;
            else
                *bitsPerPixelP = 2 * *bitsPerSampleP;
        } else {
            if (pnm_type == PPM_TYPE)
                *bitsPerPixelP = 3 * *bitsPerSampleP;
            else
                *bitsPerPixelP = *bitsPerSampleP;
        }
        if (verbose)
            pm_message("Writing %d bits per component per pixel", 
                       *bitsPerSampleP);
    }
}


static void
createPngPalette(pixel              palette_pnm[], 
                 unsigned int const paletteSize, 
                 pixval       const maxval,
                 gray               trans_pnm[],
                 unsigned int const transSize,
                 gray               alpha_maxval,
                 png_color          palette[],
                 png_byte           trans[]) {
/*----------------------------------------------------------------------------
   Create the data structure to be passed to the PNG compressor to represent
   the palette -- the whole palette, color + transparency.

   This is basically just a maxval conversion from the Netpbm-format
   equivalents we get as input.
-----------------------------------------------------------------------------*/
    unsigned int i;

    for (i = 0; i < paletteSize; ++i) {
        pixel p;
        PPM_DEPTH(p, palette_pnm[i], maxval, PALETTEMAXVAL);
        palette[i].red   = PPM_GETR(p);
        palette[i].green = PPM_GETG(p);
        palette[i].blue  = PPM_GETB(p);
#ifdef DEBUG
        pm_message("palette[%u] = (%d, %d, %d)",
                   i, palette[i].red, palette[i].green, palette[i].blue);
#endif
    }

    for (i = 0; i < transSize; ++i) {
        unsigned int const newmv = PALETTEMAXVAL;
        unsigned int const oldmv = alpha_maxval;
        trans[i] = (trans_pnm[i] * newmv + (oldmv/2)) / oldmv;
#ifdef DEBUG
        pm_message("trans[%u] = %d", i, trans[i]);
#endif
    }
}


static int 
convertpnm (FILE * const ifp, 
            FILE * const afp, 
            FILE * const pfp, 
            FILE * const tfp) {
  xel p;
  int rows, cols, format;
  xelval maxval;
      /* The maxval of the input image */
  xelval png_maxval;
      /* The maxval of the samples in the PNG output 
         (must be 1, 3, 7, 15, 255, or 65535)
      */
  pixel transcolor;
      /* The color that is to be transparent, with maxval equal to that
         of the input image.
      */
  int transexact;  
    /* boolean: the user wants only the exact color he specified to be
       transparent; not just something close to it.
    */
  unsigned int pnm_meaningful_bits;
  pixel backcolor;
      /* The background color, with maxval equal to that of the input
         image.
      */
  png_struct *png_ptr;
  png_info *info_ptr;

  bool colorMapped;
  pixel palette_pnm[MAXCOLORS];
  png_color palette[MAXCOLORS];
      /* The color part of the color/alpha palette passed to the PNG
         compressor 
      */
  unsigned int palette_size;

  gray trans_pnm[MAXCOLORS];
  png_byte  trans[MAXCOLORS];
      /* The alpha part of the color/alpha palette passed to the PNG
         compressor 
      */
  unsigned int trans_size;

  colorhash_table cht;
  coloralphahash_table caht;

  unsigned int background_index;
      /* Index into palette[] of the background color. */

  png_uint_16 histogram[MAXCOLORS];
  png_byte *line;
  png_byte *pp;
  int pass;
  gray alpha_maxval;
  int alpha_rows;
  int alpha_cols;
  int alpha_can_be_transparency_index;

  int colors;
  unsigned int depth;
      /* The number of bits per pixel in the (uncompressed) png 
         raster -- if the raster contains palette indices, this is the
         number of bits in the index.
      */
  unsigned int fulldepth;
      /* The total number of bits per pixel in the (uncompressed) png
         raster, including all channels 
      */
  int x, y;
  pm_filepos imagepos;  
      /* file position in input image file of start of image (i.e. after
         the header)
      */
  xel *xelrow;    /* malloc'ed */
      /* The row of the input image currently being processed */

  /* these variables are declared static because gcc wasn't kidding
   * about "variable XXX might be clobbered by `longjmp' or `vfork'"
   * (stack corruption observed on Solaris 2.6 with gcc 2.8.1, even
   * in the absence of any other error condition) */
  static int pnm_type;
  static xelval maxmaxval;
  static gray **alpha_mask;
  

  /* these guys are initialized to quiet compiler warnings: */
  maxmaxval = 255;
  alpha_mask = NULL;
  depth = 0;
  errorlevel = 0;

  png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING,
    &pnmtopng_jmpbuf_struct, pnmtopng_error_handler, NULL);
  if (png_ptr == NULL) {
    pm_closer (ifp);
    pm_error ("cannot allocate main libpng structure (png_ptr)");
  }

  info_ptr = png_create_info_struct (png_ptr);
  if (info_ptr == NULL) {
    png_destroy_write_struct (&png_ptr, (png_infopp)NULL);
    pm_closer (ifp);
    pm_error ("cannot allocate libpng info structure (info_ptr)");
  }

  if (setjmp (pnmtopng_jmpbuf_struct.jmpbuf)) {
    png_destroy_write_struct (&png_ptr, &info_ptr);
    pm_closer (ifp);
    pm_error ("setjmp returns error condition (1)");
  }

  pnm_readpnminit (ifp, &cols, &rows, &maxval, &format);
  pm_tell2(ifp, &imagepos, sizeof(imagepos));
  pnm_type = PNM_FORMAT_TYPE (format);

  xelrow = pnm_allocrow(cols);

  if (verbose) {
    if (pnm_type == PBM_TYPE)    
      pm_message ("reading a PBM file (maxval=%d)", maxval);
    else if (pnm_type == PGM_TYPE)    
      pm_message ("reading a PGM file (maxval=%d)", maxval);
    else if (pnm_type == PPM_TYPE)    
      pm_message ("reading a PPM file (maxval=%d)", maxval);
  }

  if (pnm_type == PGM_TYPE)
    maxmaxval = PGM_OVERALLMAXVAL;
  else if (pnm_type == PPM_TYPE)
    maxmaxval = PPM_OVERALLMAXVAL;

  if (transparent > 0) {  /* -1 or 1 are the only possibilities so far */
    char * transstring2;  
      /* Same as transstring, but with possible leading '=' removed */
    if (transstring[0] == '=') {
      transexact = 1;
      transstring2 = transstring+1;
    } else {
      transexact = 0;
      transstring2 = transstring;
    }  
    /* We do this funny PPM_DEPTH thing instead of just passing 'maxval'
       to ppm_parsecolor() because ppm_parsecolor() does a cheap maxval
       scaling, and this is more precise.
    */
    PPM_DEPTH (transcolor, ppm_parsecolor(transstring2, maxmaxval),
               maxmaxval, maxval);
  }
  if (alpha) {
    pixel alpha_transcolor;

    if (verbose)
      pm_message ("reading alpha-channel image...");
    alpha_mask = pgm_readpgm (afp, &alpha_cols, &alpha_rows, &alpha_maxval);

    if (alpha_cols != cols || alpha_rows != rows) {
      png_destroy_write_struct (&png_ptr, &info_ptr);
      pm_closer (ifp);
      pm_error ("dimensions for image and alpha mask do not agree");
    }
    alpha_trans(ifp, imagepos, cols, rows, maxval, format, 
                alpha_mask, alpha_maxval,
                &alpha_can_be_transparency_index, &alpha_transcolor);

    if (alpha_can_be_transparency_index && !force) {
      if (verbose)
        pm_message ("converting alpha mask to transparency index");
      alpha = FALSE;
      transparent = 2;
      transcolor = alpha_transcolor;
    } else {
      transparent = -1;
    }
  } else
      /* Though there's no alpha_mask, we still need an alpha_maxval for
         use with trans[], which can have stuff in it if the user specified
         a transparent color.
      */
      alpha_maxval = 255;

  /* gcc 2.7.0 -fomit-frame-pointer causes stack corruption here */
  if (background > -1) 
      PPM_DEPTH(backcolor, ppm_parsecolor (backstring, maxmaxval), 
                maxmaxval, maxval);;

  /* first of all, check if we have a grayscale image written as PPM */

  if (pnm_type == PPM_TYPE && !force) {
    int isgray = TRUE;

    pm_seek2(ifp, &imagepos, sizeof(imagepos));
    for (y = 0 ; y < rows && isgray ; y++) {
      pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
      for (x = 0 ; x < cols && isgray ; x++) {
        p = xelrow[x];
        if (PPM_GETR (p) != PPM_GETG (p) || PPM_GETG (p) != PPM_GETB (p))
          isgray = FALSE;
      }
    }
    if (isgray)
      pnm_type = PGM_TYPE;
  }

  /* handle `odd' maxvalues */

    if (maxval > 65535 && !downscale) {
      png_destroy_write_struct (&png_ptr, &info_ptr);
      pm_closer (ifp);
      pm_error ("can only handle files up to 16-bit "
                "(use -downscale to override");
    }

  findRedundantBits(ifp, imagepos, cols, rows, maxval, format, alpha,
                    force, &pnm_meaningful_bits);
  
  /* -----------------------------------------------------------------
     Determine whether to do a colormapped or truecolor PNG (variable
     'colorMapped'), and if colormapped, compute the full PNG palette
     -- both color and transparency -- as the arrays palette_pnm[]
     and trans_pnm[], with sizes palette_size and trans_size.
  -------------------------------------------------------------------- */

  if (force)
      colorMapped = FALSE;
  else if (pnm_type == PBM_TYPE)
      colorMapped = FALSE;
  else if (maxval > PALETTEMAXVAL)
      colorMapped = FALSE;
  else {
      colorhist_vector chv;

      getChv(ifp, imagepos, cols, rows, maxval, format, MAXCOLORS, 
             &chv, &colors);

      if (chv == NULL) {
          if (pfp)
              pm_error("You specified -palette, but there are more than %d "
                       "colors in the "
                       "image -- too many for a colormapped PNG", MAXCOLORS);
          else {
              colorMapped = FALSE;
              if (verbose)
                  pm_message("More than %d colors found -- too many for a "
                             "colormapped PNG", MAXCOLORS);
          }
      } else {
          if (!pfp && ((pnm_type == PGM_TYPE && pm_maxvaltobits(colors-1) > 
               (pm_maxvaltobits(maxval) / 2)) ||
              (pnm_type == PPM_TYPE && maxval > 255))) {
              
              colorMapped = FALSE;
              if (verbose) 
                  pm_message ("palette index would be larger than the "
                              "indexed value, so not doing colormap");
          } else {
              if (alpha) {
                  bool tooBig;
                  if (pfp)
                      pm_error("This program is not capable of generating "
                               "a PNG with transparency when you specify "
                               "the palette with -palette.");
                  compute_alpha_palette(ifp, cols, rows, maxval, format, 
                                        imagepos,  alpha_mask,
                                        palette_pnm, trans_pnm, 
                                        &palette_size, &trans_size,
                                        &tooBig);
                  if (tooBig) {
                      colorMapped = FALSE;
                      if (verbose)
                          pm_message("too many color/transparency pairs, "
                                     "writing a non-mapped file");
                  } else
                      colorMapped = TRUE;
              } else {
                  colorMapped = TRUE;
                  compute_nonalpha_palette(chv, colors, maxval, pfp,
                                           palette_pnm, &palette_size, 
                                           trans_pnm, &trans_size);

                  if (transparent != -1)
                      makeOneColorTransparentInPalette(
                          transcolor, transexact, 
                          palette_pnm, palette_size, trans_pnm, &trans_size);
              }
              
              if (background > -1) {
                  findOrAddBackgroundInPalette(
                      backcolor, palette_pnm, &palette_size, 
                      &background_index);
              }
          }
      }
  }
  
  computeColorMapLookupTable(colorMapped, palette_pnm, palette_size,
                             trans_pnm, trans_size, alpha, alpha_maxval,
                             &cht, &caht);

  computePixelWidth(colorMapped, palette_size, pnm_type, 
                    pnm_meaningful_bits, alpha,
                    &depth, &fulldepth);
  if (verbose)
    pm_message ("writing a%s %d-bit %s%s file%s",
                fulldepth == 8 ? "n" : "", fulldepth,
                colorMapped ? "palette": 
                (pnm_type == PPM_TYPE ? "RGB" : "gray"),
                alpha ? (colorMapped ? "+transparency" : "+alpha") : "",
                interlace? " (interlaced)" : "");

  /* now write the file */

  png_maxval = pm_bitstomaxval(depth);

  if (setjmp (pnmtopng_jmpbuf_struct.jmpbuf)) {
    png_destroy_write_struct (&png_ptr, &info_ptr);
    pm_closer (ifp);
    pm_error ("setjmp returns error condition (2)");
  }

  png_init_io (png_ptr, stdout);
  info_ptr->width = cols;
  info_ptr->height = rows;
  info_ptr->bit_depth = depth;

  if (colorMapped)
    info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
  else if (pnm_type == PPM_TYPE)
    info_ptr->color_type = PNG_COLOR_TYPE_RGB;
  else
    info_ptr->color_type = PNG_COLOR_TYPE_GRAY;

  if (alpha && info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
    info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;

  info_ptr->interlace_type = interlace;

  /* gAMA chunk */
  if (gamma != -1.0) {
    info_ptr->valid |= PNG_INFO_gAMA;
    info_ptr->gamma = gamma;
  }

  /* cHRM chunk */
  if (chroma_wx != -1.0) {
    info_ptr->valid |= PNG_INFO_cHRM;
    info_ptr->x_white = chroma_wx;
    info_ptr->y_white = chroma_wy;
    info_ptr->x_red = chroma_rx;
    info_ptr->y_red = chroma_ry;
    info_ptr->x_green = chroma_gx;
    info_ptr->y_green = chroma_gy;
    info_ptr->x_blue = chroma_bx;
    info_ptr->y_blue = chroma_by;
  }

  /* pHYS chunk */
  if (phys_unit != -1.0) {
    info_ptr->valid |= PNG_INFO_pHYs;
    info_ptr->x_pixels_per_unit = phys_x;
    info_ptr->y_pixels_per_unit = phys_y;
    info_ptr->phys_unit_type = phys_unit;
  }

  if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE) {

    /* creating PNG palette  (PLTE and tRNS chunks) */

    createPngPalette(palette_pnm, palette_size, maxval,
                     trans_pnm, trans_size, alpha_maxval, 
                     palette, trans);
    info_ptr->valid |= PNG_INFO_PLTE;
    info_ptr->palette = palette;
    info_ptr->num_palette = palette_size;
    if (trans_size > 0) {
        info_ptr->valid |= PNG_INFO_tRNS;
        info_ptr->trans = trans;
        info_ptr->num_trans = trans_size;   /* omit opaque values */
    }
    /* creating hIST chunk */
    if (hist) {
        colorhist_vector chv;
        int colors;
        colorhash_table cht;
        
        getChv(ifp, imagepos, cols, rows, maxval, format, MAXCOLORS, 
               &chv, &colors);

        cht = ppm_colorhisttocolorhash (chv, colors);
                
        { 
            unsigned int i;
            for (i = 0 ; i < MAXCOLORS; ++i) {
                int const chvIndex = ppm_lookupcolor(cht, &palette_pnm[i]);
                if (chvIndex == -1)
                    histogram[i] = 0;
                else
                    histogram[i] = chv[chvIndex].value;
            }
        }

        ppm_freecolorhash(cht);

        info_ptr->valid |= PNG_INFO_hIST;
        info_ptr->hist = histogram;
        if (verbose)
            pm_message ("histogram created");
    }
  } else { /* color_type != PNG_COLOR_TYPE_PALETTE */
    if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY ||
        info_ptr->color_type == PNG_COLOR_TYPE_RGB) {
        if (transparent > 0) {
            info_ptr->valid |= PNG_INFO_tRNS;
            info_ptr->trans_values = 
                xelToPngColor_16(transcolor, maxval, png_maxval);
        }
    } else {
        /* This is PNG_COLOR_MASK_ALPHA.  Transparency will be handled
           by the alpha channel, not a transparency color.
        */
    }
    if (verbose) {
        if (info_ptr->valid && PNG_INFO_tRNS) 
            pm_message("Transparent color {gray, red, green, blue} = "
                       "{%d, %d, %d, %d}",
                       info_ptr->trans_values.gray,
                       info_ptr->trans_values.red,
                       info_ptr->trans_values.green,
                       info_ptr->trans_values.blue);
        else
            pm_message("No transparent color");
    }
  }

  freeChv();

  /* bKGD chunk */
  if (background > -1) {
      info_ptr->valid |= PNG_INFO_bKGD;
      if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE) {
          info_ptr->background.index = background_index;
      } else {
          info_ptr->background = 
              xelToPngColor_16(backcolor, maxval, png_maxval);
          if (verbose)
              pm_message("Writing bKGD chunk with background color "
                         " {gray, red, green, blue} = {%d, %d, %d, %d}",
                         info_ptr->background.gray, 
                         info_ptr->background.red, 
                         info_ptr->background.green, 
                         info_ptr->background.blue ); 
      }
  }

  if (!colorMapped && (png_maxval != maxval || 
                       (alpha && png_maxval != alpha_maxval))) {
    /* We're writing in a bit depth that doesn't match the maxval of the
       input image and the alpha mask.  So we write an sBIT chunk to tell
       what the original image's maxval was.  The sBit chunk doesn't let
       us specify any maxval -- only powers of two minus one.  So we pick
       the power of two minus one which is greater than or equal to the
       actual input maxval.
    */
    /* sBIT chunk */
    int sbitval;

    info_ptr->valid |= PNG_INFO_sBIT;

    sbitval = pm_maxvaltobits(maxval);

    if (info_ptr->color_type & PNG_COLOR_MASK_COLOR) {
      info_ptr->sig_bit.red   = sbitval;
      info_ptr->sig_bit.green = sbitval;
      info_ptr->sig_bit.blue  = sbitval;
    } else {
      info_ptr->sig_bit.gray = sbitval;
    }
    if (verbose)
        pm_message("Writing sBIT chunk with sbitval = %d", sbitval);

    if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA) {
      info_ptr->sig_bit.alpha = pm_maxvaltobits(alpha_maxval);
    }
  }

  /* tEXT and zTXT chunks */
  if ((text) || (ztxt)) {
    pnmpng_read_text (info_ptr, tfp, ztxt, verbose);
  }

  /* tIME chunk */
  if (mtime) {
    info_ptr->valid |= PNG_INFO_tIME;
    sscanf (date_string, "%d-%d-%d", &time_struct.tm_year,
                                     &time_struct.tm_mon,
                                     &time_struct.tm_mday);
    if (time_struct.tm_year > 1900)
      time_struct.tm_year -= 1900;
    time_struct.tm_mon--; /* tm has monthes 0..11 */
    sscanf (time_string, "%d:%d:%d", &time_struct.tm_hour,
                                     &time_struct.tm_min,
                                     &time_struct.tm_sec);
    png_convert_from_struct_tm (&info_ptr->mod_time, &time_struct);
  }

  /* explicit filter-type (or none) required */
  if ((filter >= 0) && (filter <= 4))
  {
    png_set_filter (png_ptr, 0, filter);
  }

  /* zlib compression-level (or none) required */
  if ((compression >= 0) && (compression <= 9))
  {
    png_set_compression_level (png_ptr, compression);
  }

  /* write the png-info struct */
  png_write_info (png_ptr, info_ptr);

  if ((text) || (ztxt))
    /* prevent from being written twice with png_write_end */
    info_ptr->num_text = 0;

  if (mtime)
    /* prevent from being written twice with png_write_end */
    info_ptr->valid &= ~PNG_INFO_tIME;

  /* let libpng take care of, e.g., bit-depth conversions */
  png_set_packing (png_ptr);

  /* Write the raster */
 
  /* max: 3 color channels, one alpha channel, 16-bit */
  MALLOCARRAY(line, cols * 8);
  if (line == NULL)
  {
    png_destroy_write_struct (&png_ptr, &info_ptr);
    pm_closer (ifp);
    pm_error ("out of memory allocating PNG row buffer");
  }

  for (pass = 0 ; pass < png_set_interlace_handling (png_ptr) ; pass++) {
      unsigned int row;
      pm_seek2(ifp, &imagepos, sizeof(imagepos));
      for (row = 0; row < rows; ++row) {
          unsigned int col;
          pnm_readpnmrow(ifp, xelrow, cols, maxval, format);
          pnm_promoteformatrow(xelrow, cols, maxval, format, maxval, PPM_TYPE);
          pp = line;
          for (col = 0 ; col < cols ; ++col) {
              xel p_png;
              xel const p = xelrow[col];
              PPM_DEPTH(p_png, p, maxval, png_maxval);
              if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY ||
                  info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
                  if (depth == 16)
                      *pp++ = PNM_GET1 (p_png) >> 8;
                  *pp++ = PNM_GET1 (p_png)&0xff;
              } else if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE) {
                  unsigned int paletteIndex;
                  if (alpha)
                      paletteIndex = lookupColorAlpha(caht, &p, 
                                                      &alpha_mask[row][col]);
                  else
                      paletteIndex = ppm_lookupcolor(cht, &p);
                  *pp++ = paletteIndex;
              } else if (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
                         info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
                  if (depth == 16)
                      *pp++ = PPM_GETR (p_png) >> 8;
                  *pp++ = PPM_GETR (p_png)&0xff;
                  if (depth == 16)
                      *pp++ = PPM_GETG (p_png) >> 8;
                  *pp++ = PPM_GETG (p_png)&0xff;
                  if (depth == 16)
                      *pp++ = PPM_GETB (p_png) >> 8;
                  *pp++ = PPM_GETB (p_png)&0xff;
              } else {
                  png_destroy_write_struct (&png_ptr, &info_ptr);
                  pm_closer (ifp);
                  pm_error (" (can't happen) undefined color_type");
              }
              if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA) {
                  int const png_alphaval = (int)
                      alpha_mask[row][col] * (float) png_maxval / maxval +0.5;
                  if (depth == 16)
                      *pp++ = png_alphaval >> 8;
                  *pp++ = png_alphaval & 0xff;
              }
          }
          png_write_row (png_ptr, line);
      }
  }
  png_write_end (png_ptr, info_ptr);


#if 0
  /* The following code may be intended to solve some segfault problem
     that arises with png_destroy_write_struct().  The latter is the
     method recommended in the libpng documentation and this program 
     will not compile under Cygwin because the Windows DLL for libpng
     does not contain png_write_destroy() at all.  Since the author's
     comment below does not make it clear what the segfault issue is,
     we cannot consider it.  -Bryan 00.09.15
*/

  png_write_destroy (png_ptr);
  /* flush first because free(png_ptr) can segfault due to jmpbuf problems
     in png_write_destroy */
  fflush (stdout);
  free (png_ptr);
  free (info_ptr);
#else
  png_destroy_write_struct(&png_ptr, &info_ptr);
#endif

  pnm_freerow(xelrow);

  if (cht)
      ppm_freecolorhash(cht);
  if (caht)
      freecoloralphahash(caht);

  return errorlevel;
}



static void
displayVersion() {

    fprintf(stderr,"pnmtopng version %s.\n", VERSION);

    /* We'd like to display the version of libpng with which we're
       linked, as we do for zlib, but it isn't practical.
       While libpng is capable of telling you what it's level
       is, different versions of it do it two different ways: with
       png_libpng_ver or with png_get_header_ver.  So we have to be
       compiled for a particular version just to find out what
       version it is! It's not worth having a link failure, much
       less a compile failure, if we choose wrong.
       png_get_header_ver is no in anything older than libpng 1.0.2a
       (Dec 1998).  png_libpng_ver is not there in libraries built
       without USE_GLOBAL_ARRAYS.  Cygwin versions are normally built
       without USE_GLOBAL_ARRAYS.  -bjh 2002.06.17.
    */
    fprintf(stderr, "   Compiled with libpng %s.\n",
            PNG_LIBPNG_VER_STRING);
    fprintf(stderr, "   Compiled with zlib %s; using zlib %s.\n",
            ZLIB_VERSION, zlib_version);
    fprintf(stderr,    
            "   Compiled with %d-bit netpbm support "
            "(PPM_OVERALLMAXVAL = %d).\n",
            pm_maxvaltobits (PPM_OVERALLMAXVAL), PPM_OVERALLMAXVAL);
    fprintf(stderr, "\n");
}



int 
main(int argc, char *argv[]) {

  FILE *ifp, *tfp, *afp, *pfp;
  char *palette_file;
      /* Name of user-supplied palette, file; NULL if none */
  int argn, errorlevel=0;

  const char * const usage = "[-verbose] [-downscale] [-interlace] [-force] [-alpha file] ...\n\
             ... [-transparent color] [-background color] [-gamma value] ...\n\
             ... [-hist] [-chroma wx wy rx ry gx gy bx by] [-phys x y unit] ...\n\
             ... [-text file] [-ztxt file] [-time [yy]yy-mm-dd hh:mm:ss] ...\n\
             ... [-palette file] [-filter 0..4] [-compression 0..9] [pnmfile]";

  pnm_init (&argc, argv);
  argn = 1;

  palette_file = NULL;   /* Initial value */

  while (argn < argc && argv[argn][0] == '-' && argv[argn][1] != '\0') {
    if (pm_keymatch (argv[argn], "-verbose", 2)) {
      verbose = TRUE;
    } else
    if (pm_keymatch (argv[argn], "-downscale", 2)) {
      downscale = TRUE;
    } else
    if (pm_keymatch (argv[argn], "-interlace", 2)) {
      interlace = TRUE;
    } else
    if (pm_keymatch (argv[argn], "-alpha", 2)) {
      if (transparent > 0)
        pm_error ("-alpha and -transparent are mutually exclusive");
      alpha = TRUE;
      if (++argn < argc)
        alpha_file = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-transparent", 3)) {
      if (alpha)
        pm_error ("-alpha and -transparent are mutually exclusive");
      transparent = 1;
      if (++argn < argc)
        transstring = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-background", 2)) {
      background = 1;
      if (++argn < argc)
        backstring = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-gamma", 2)) {
      if (++argn < argc)
        sscanf (argv[argn], "%f", &gamma);
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-hist", 2)) {
      hist = TRUE;
    } else
    if (pm_keymatch (argv[argn], "-chroma", 3)) {
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_wx);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_wy);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_rx);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_ry);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_gx);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_gy);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_bx);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%f", &chroma_by);
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-phys", 3)) {
      if (++argn < argc)
        sscanf (argv[argn], "%d", &phys_x);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%d", &phys_y);
      else
        pm_usage (usage);
      if (++argn < argc)
        sscanf (argv[argn], "%d", &phys_unit);
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-text", 3)) {
      text = TRUE;
      if (++argn < argc)
        text_file = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-ztxt", 2)) {
      ztxt = TRUE;
      if (++argn < argc)
        text_file = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-time", 3)) {
      mtime = TRUE;
      if (++argn < argc) {
        date_string = argv[argn];
        if (++argn < argc)
          time_string = argv[argn];
        else
          pm_usage (usage);
      } else {
        pm_usage (usage);
      }
    } else 
    if (pm_keymatch (argv[argn], "-palette", 3)) {
      if (++argn < argc)
        palette_file = argv[argn];
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-filter", 3)) {
      if (++argn < argc)
      {
        sscanf (argv[argn], "%d", &filter);
        if ((filter < 0) || (filter > 4))
        {
          pm_message
            ("filter must be 0 (none), 1 (sub), 2 (up), 3 (avg) or 4 (paeth)");
          pm_usage (usage);
        }
      }
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-compression", 3)) {
      if (++argn < argc)
      {
        sscanf (argv[argn], "%d", &compression);
        if ((compression < 0) || (compression > 9))
        {
          pm_message ("zlib compression must be between 0 (none) and 9 (max)");
          pm_usage (usage);
        }
      }
      else
        pm_usage (usage);
    } else
    if (pm_keymatch (argv[argn], "-force", 3)) {
      force = TRUE;
    } else 
      displayVersion();  /* exits program */
    argn++;
  }

  { 
      const char *input_file;
      if (argn == argc)
          input_file = "-";
      else {
          input_file = argv[argn];
          argn++;
      }
      ifp = pm_openr_seekable(input_file);
  }

  if (argn != argc)
    pm_usage (usage);

  if (alpha)
    afp = pm_openr (alpha_file);
  else
    afp = NULL;

  if (palette_file)
    pfp = pm_openr (palette_file);
  else
    pfp = NULL;

  if ((text) || (ztxt))
    tfp = pm_openr (text_file);
  else
    tfp = NULL;

  errorlevel = convertpnm(ifp, afp, pfp, tfp);

  if (afp)
    pm_closer (afp);
  if (pfp)
    pm_closer (pfp);
  if (tfp)
    pm_closer (tfp);

  pm_closer (ifp);
  pm_closew (stdout);

  return errorlevel;
}
