Provided by: libnetpbm10-dev_10.0-15_amd64 bug

NAME

       libppm - functions to support portable pixmap (PPM) programs

SYNOPSIS

       #include <ppm.h>

       void ppm_init( int *argcP, char *argv[] );

       pixel ** ppm_allocarray( int cols, int rows );

       pixel * ppm_allocrow( int cols );

       void ppm_freearray( pixel **pixels, int rows );

       void ppm_freerow( pixel *pixelrow);

       void ppm_readppminit( FILE *fp, int *colsP, int *rowsP, pixval *maxvalP, int *formatP );

       void ppm_readppmrow( FILE *fp, pixel *pixelrow, int cols, pixval maxval, int format );

       pixel ** ppm_readppm( FILE *fp, int *colsP, int *rowsP, pixvalP *maxvalP );

       void ppm_writeppminit( FILE *  fp , int cols, int rows, pixval maxval, int forceplain );

       void  ppm_writeppmrow(  FILE *fp, pixel *pixelrow, int cols, pixval maxval, int forceplain
       );

       void ppm_writeppm( FILE *fp, pixel ** pixels, int  cols,  int  rows,  pixval  maxval,  int
       forceplain );

       void  ppm_writeppm(  FILE  *fp,  pixel  **pixels,  int  cols, int rows, pixval maxval, int
       forceplain );

       void ppm_nextimage( FILE *file, int * const eofP);

       void ppm_check( FILE * file, const enum pm_check_type check_type, const int format,  const
       int cols, const int rows, const int maxval,
       enum pm_check_code * const retval);

       typedef ... pixel; typedef ... pixval;

       #define PPM_MAXMAXVAL ...

       #define PPM_OVERALLMAXVAL ...

       #define PPM_FORMAT ...

       #define RPPM_FORMAT ...

       #define PPM_TYPE PPM_FORMAT

       #define PPM_FORMAT_TYPE(format) ...

       extern pixval ppm_pbmmaxval;

       pixval PPM_GETR( pixel p) pixval PPM_GETG( pixel p) pixval PPM_GETB( pixel p)

       void PPM_ASSIGN( pixel p, pixval red, pixval grn, pixval blu)

       int PPM_EQUAL( pixel p, pixel q)

       void PPM_DEPTH( pixel newp, pixel p, pixval oldmaxval, pixval newmaxval)

       float PPM_LUMIN( pixel p)

       float PPM_CHROM_R( pixel p)

       float PPM_CHROM_B( pixel p)

       pixel ppm_parsecolor( char *colorname, pixval maxval)

       char * ppm_colorname( pixel *colorP, pixval maxval, int hexok)

DESCRIPTION

   TYPES AND CONSTANTS
       Each  pixel contains three pixvals, each of which should contain only the values between 0
       and PPM_MAXMAXVAL.  ppm_pbmmaxval is the maxval used when a PPM program reads a PBM  file.
       Normally it is 1; however, for some programs, a larger value gives better results.

   MANIPULATING PIXELS
       The  macros  PPM_GETR,  PPM_GETG,  and  PPM_GETB  retrieve the red, green, or blue sample,
       respectively, from the given pixel.

       The PPM_ASSIGN macro assigns the given values to the red, green, and blue samples  of  the
       given pixel.

       The PPM_EQUAL macro tests two pixels for equality.

       The  PPM_DEPTH  macro  scales  the colors of pixel p according the old and new maxvals and
       assigns the new values to newp.  It is intended to make writing ppmtowhatever easier.

       The  PPM_LUMIN,  PPM_CHROM_R,  and  PPM_CHROM_B,  macros  determine  the  luminance,   red
       chrominance,  and  blue chrominance, respectively, of the pixel p.  The scale of all these
       values is the same as the scale of the input samples (i.e.  0  to  maxval  for  luminance,
       -maxval/2 to maxval/2 for chrominance).

       Note  that  the macros do it by floating point multiplication.  If you are computing these
       values over an entire image, it may be significantly faster to do it  with  multiplication
       tables  instead.   Compute  all  the possible products once up front, then for each pixel,
       just look up the products in the tables.

   INITIALIZATION
       All PPM programs must call ppm_init() just after invocation,  before  they  process  their
       arguments.

   MEMORY MANAGEMENT
       ppm_allocarray() allocates an array of pixels.

       ppm_allocrow() allocates a row of the given number of pixels.

       ppm_freearray()  frees  the  array  allocated  with  ppm_allocarray() containing the given
       number of rows.

       ppm_freerow() frees a row of pixelss allocated with ppm_allocrow().

   READING FILES
       If a function in this section is called on a PBM or PGM format file, it translates the PBM
       or  PGM  file  into  a  PPM  file  on  the  fly  and functions as if it were called on the
       equivalent PPM file.  The format value returned  by  ppm_readppminit()  is,  however,  not
       translated.  It represents the actual format of the PBM or PGM file.

       ppm_readppminit()  reads  the header of a PPM file, returning all the information from the
       header and leaving the file positioned just after the header.

       ppm_readppmrow() reads a row of pixels into the pixelrow array.  format, cols, and  maxval
       are the values returned by ppm_readppminit().

       ppm_readppm()  reads an entire PPM image into memory, returning the allocated array as its
       return value and returning the information from the header  as  rows,  cols,  and  maxval.
       This function combines ppm_readppminit(), ppm_allocarray(), and ppm_readppmrow().

   WRITING FILES
       ppm_writeppminit()  writes  the  header for a PPM file and leaves it positioned just after
       the header.

       forceplain is a logical value that tells ppm_writeppminit() to write a header for a  plain
       PPM format file, as opposed to a raw PPM format file.

       ppm_writeppmrow()  writes  the  row pixelrow to a PPM file.  For meaningful results, cols,
       maxval, and forceplain must be the same as was used with ppm_writeppminit().

       ppm_writeppm() write the header and all data for a  PPM  image.   This  function  combines
       ppm_writeppminit() and ppm_writeppmrow().

   MISCELLANEOUS
       ppm_nextimage()  positions  a PPM input file to the next image in it (so that a subsequent
       ppm_readppminit() reads its header).

       ppm_nextimage() is analogous to pbm_nextimage(), but works on PPM, PGM, and PBM files.

       ppm_check() checks for the common file integrity error where the file is the wrong size to
       contain all the image data.

       ppm_check() is analogous to pbm_check(), but works on PPM, PGM, and PBM files.

   COLOR NAMES
       ppm_parsecolor() Interprets a color specification and returns a pixel of the color that it
       indicates.  The color specification is ASCII text, in one of three formats:  1) a name, as
       defined  in  the  system's  X11-style  color  names file (e.g.  rgb.txt).  2) an X11-style
       hexadecimal triple: #rgb, #rrggbb, #rrrgggbbb, or #rrrrggggbbbb.  3) A triplet of  decimal
       floating  point  numbers  from  0.0  to 1.0, representing red, green, and blue intensities
       respectively, separated by commas.  E.g. "1.0, 0.5, .25".

       If the color specification does not conform to any of these formats,  including  the  case
       that  it is a name, but is not in the rgb.txt database, ppm_parsecolor() exits the program
       via pm_error().

       ppm_colorname() Returns a string that describes the color  of  the  given  pixel.   If  an
       X11-style  color  names  file  (e.g.   rgb.txt)  is available and the color appears in it,
       ppm_colorname() returns the name of the color from the file.  If the color does not appear
       in  a  X11-style color file and hexok is true, ppm_colorname() returns a hexadecimal color
       specification triple (#rrggbb).  If a X11-style color file is available but the color does
       not  appear  in  it  and  hexok  is false, ppm_colorname() returns the name of the closest
       matching color in the color file.  Finally, if their is no X11-style color file  available
       and hexok is false, ppm_colorname() fails and exits the program with an error message.

       The string returned is in static libppm library storage which is overwritten by every call
       to ppm_colorname().

   COLOR INDEXING
       Sometimes in processing images, you want to associate a value  with  a  particular  color.
       Most  often,  that's because you're generating a color mapped graphics format.  In a color
       mapped graphics format, the raster contains small numbers, and the file contains  a  color
       map  that  tells what color each of those small numbers refers to.  If your image has only
       256 colors, but each color takes 24 bits to describe, this can make your output file  much
       smaller than a straightforward RGB raster would.

       So,  continuing  the  above example, say you have a pixel value for chartreuse and in your
       output file and you are going to represent chartreuse by the number 12.  You need  a  data
       structure  that  allows  your program quickly to find out that the number for a chartreuse
       pixel is 12.  Netpbm's color indexing data types and functions give you that.

       colorhash_table is a C data type that associates an integer  with  each  of  an  arbitrary
       number  of colors.  It is a hash table, so it uses far less space than an array indexed by
       the color's RGB values would.

       The problem with a colorhash_table is that you can only look things up in it.   You  can't
       find out what colors are in it.  So Netpbm has another data type for representing the same
       information, the poorly but historically named colorhist_vector.   A  colorhist_vector  is
       just  an array.  Each entry represents a color and contains the color's value (as a pixel)
       and the integer value associated with  it.   The  entries  are  filled  in  starting  with
       subscript 0 and going consecutively up for the number of colors in the histogram.

       (The  reason the name is poor is because a color histogram is only one of many things that
       could be represented by it).

       colorhash_table ppm_alloccolorhash()

       This creates a colorhash_table using dynamically allocated storage.  There are  no  colors
       in it.  If there is not enough storage, it exits the program with an error message.

       void ppm_freecolorhash()

       This destroys a ppm_freecolorhash and frees all the storage associated with it.

       int ppm_addtocolorhash( colorhash_table cht, const pixel * const colorP, const int value)

       This  adds  the  specified  color  to  the  specified  colorhash_table  and associates the
       specified value with it.

       You  must  ensure  that  the  color  you  are  adding  isn't  already   present   in   the
       colorhash_table.

       There is no way to update an entry or delete an entry from a colorhash_table.

       int ppm_lookupcolor( const colorhash_table cht, const pixel * const colorP )

       This  looks  up  the  specified  color  in  the specified colorhash_table.  It returns the
       integer value associated with that color.

       If the specified color is not in the hash table, the function  returns  -1.   (So  if  you
       assign the value -1 to a color, the return value is ambiguous).

       colorhist_vector ppm_colorhashtocolorhist( const colorhash_table cht, const int ncolors )

       This  converts  a  colorhash_table  to  a  colorhist_vector.   The  return  value is a new
       colorhist_vector which you must eventually free with ppm_freecolorhist().

       ncolors  is  the  number  of  colors  in  cht.   If  it  has  more   colors   than   that,
       ppm_colorhashtocolorhist does not create a colorhist_vector and returns NULL.

       colorhash_table ppm_colorhisttocolorhash( const colorhist_vector chv, const int ncolors )

       This poorly named function does not convert from a colorhist_vector to a colorhash_table.

       It  does create a colorhash_table based on a colorhist_vector input, but the integer value
       for a given color in the output is not the same as the integer value for that  same  color
       in the input.  ppm_colorhisttocolorhash() ignores the integer values in the input.  In the
       output, the integer value for a color is the index in the input colorhist_vector for  that
       color.

       You  can easily create a color map for an image by running ppm_computecolorhist() over the
       image, then ppm_colorhisttocolorhash() over the result.  Now you can use ppm_lookupcolor()
       to find a unique color index for any pixel in the input.

       If  the same color appears twice in the input, ppm_colorhisttocolorhash() exit the program
       with an error message.

       ncolors is the number of colors in chv.

       The  return  value  is  a  new  colorhash_table  which  you  must  eventually  free   with
       ppm_freecolorhash().

   COLOR HISTOGRAMS
       The  Netpbm  libraries  give  you  functions  to examine a Netpbm image and determine what
       colors are in it and how many pixels of each color are in it.  This information  is  known
       as  a  color  histogram.   Netpbm  uses its colorhash_table data type to represent a color
       histogram.

       colorhash_table ppm_computecolorhash( pixel ** const pixels, const  int  cols,  const  int
       rows, const int maxcolors, int* const colorsP )

       This  poorly  but  historically named function generates a colorhash_table whose value for
       each color is the number of pixels in a specified image that have  that  color.   (I.e.  a
       color histogram).  As a bonus, it returns the number of colors in the image.

       (It's  poorly  named because not all colorhash_tables are color histograms, but that's all
       it generates).

       pixels, cols, and rows describe the input image.

       maxcolors is the maximum number of colors you want processed.  If there  are  more  colors
       that  that in the input image, ppm_computecolorhash() returns NULL as its return value and
       stops processing as soon as it discovers this.  This makes it  run  faster  and  use  less
       memory.   One use for maxcolors is when you just want to find out whether or not the image
       has more than N colors and don't want to wait to generate a huge color table  if  so.   If
       you don't want any limit on the number of colors, specify maxcolors=0.

       ppm_computecolorhash()  returns  the actual number of colors in the image as *colorsP, but
       only if it is less than or equal to maxcolors.

       colorhash_table ppm_computecolorhash2( FILE * const ifp, const int cols, const  int  rows,
       const pixval maxval, const int format, const int maxcolors, int* const colorsP )

       This  is  the same as ppm_computecolorhash() except that instead of feeding it an array of
       pixels in storage, you give it an open file stream and it reads the image from  the  file.
       The  file  must  be  positioned after the header, at the raster.  Upon return, the file is
       still open, but its position is undefined.

       maxval and format are the values for the image (i.e. information from the file's header).

       colorhist_vector ppm_computecolorhist( pixel ** pixels, int cols, int rows, int maxcolors,
       int * colorsP )

       This is like ppm_computecolorhash() except that it creates a colorhist_vector instead of a
       colorhash_table.

       If you supply a nonzero maxcolors argument, that is  the  maximum  number  of  colors  you
       expect  to  find  in the input image.  If there are more colors than you say in the image,
       ppm_computecolorhist() returns a null pointer as its return value and  nothing  meaningful
       as *colorsP.

       If  not,  the function returns the new colorhist_vector as its return value and the actual
       number of colors in the image as *colorsP.  The returned array has space allocated for the
       specified  number  of colors regardless of how many actually exist.  The extra space is at
       the high end of the array and is available for your use in expanding the colorhist_vector.

       If you specify maxcolors=0, there is no limit on the number of  colors  returned  and  the
       return  array  has  space for 5 extra colors at the high end for your use in expanding the
       colorhist_vector.

       colorhist_vector ppm_computecolorhist2( FILE * ifp,
       int cols, int rows, int maxcolors, pixval maxval, int format,
       int * colorsP )

       This is the same as ppm_computecolorhist() except that instead of feeding it an  array  of
       pixels  in  storage, you give it an open file stream and it reads the image from the file.
       The file must be positioned after the header, at the raster.  Upon  return,  the  file  is
       still open, but its position is undefined.

SEE ALSO

       pbm(5), pgm(5), libpbm(3)

AUTHOR

       Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.

                                                                                        libppm(3)