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libpm(3) [centos man page]

Libnetbpm Utility Functions(3)				     Library Functions Manual				    Libnetbpm Utility Functions(3)

       Table Of Contents <#toc>

       These library functions are part of Netpbm(1)

       This page documents functions in the Netpbm subroutine library that are not directly related to image data.

       For introductory and general information using libnetpbm, see LibnetpbmUser'sGuide(1)

       The  most  commonly  used  libnetpbm functions are those that read and write and process Netpbm images.	Those are documented in Libnetpbm-
       NetpbmImageProcessing Manual (1)

       To use these services, #include pam.h.

Functions
   Initialization
       Overview

       void pm_init( const char * progname, unsigned int flags );

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

       Description

       All Netpbm programs must call pm_proginit() just after startup, before they process their arguments.  pm_proginit(),  among  other  things,
       processes Netpbm universal arguments and removes them from the argument list.

       A  program  that  isn't	a  Netpbm  program, but just uses libnetpbm services, need not invoke pm_proginit.  But such a program must invoke
       pm_init().

       By 'Netpbm program,' we mean a program that is part of the Netpbm package or is intended to act like one.  pm_proginit() does  things  that
       all Netpbm programs do by convention.  For example, it scans the argument list for
	common options <index.html#commonoptions> , handles them, and removes them from the argument list.  Ergo, if you want your program to have
       the same common options as those in the Netpbm package, you might use pm_proginit(), and if you don't, you must not.

       pm_proginit() is primarily intended for Netpbm developers, so you should not expect it to have stable function  across  releases,  and  you
       must go to the comments in the source code to see exactly what it does.

       Any  program  that uses libnetpbm but does not call pm_proginit (i.e. is not a Netpbm program) must call pm_init().  The conventional place
       to do this is at the very beginning of the program.  This sets up some program-global variables for use by the libnetpbm functions.

       The progname argument is the program name for libnetpbm functions to use in messages they issue.  Normally, you would use argv[0] for this.

       flags is meaningless, but for forward compatibility, you must set it to zero.

       pm_init() and pm_proginit() have been around at least since Netpbm 9.25 (March 2002).  Another function named  pm_init()  exists  in  older
       Netpbm, but was for internal use.  Netpbm programs of that era use pbm_init(), etc to do what pm_proginit() does today.	Today, pbm_init(),
       etc. exist for backward compatibility and are identical the pm_proginit().

   File Or Image Stream Access
       Overview

       FILE *pm_openr( char * name );

       FILE *pm_openw( char * name );

       FILE *pm_openr_seekable( const char * name );

       FILE *pm_close( FILE * fp );

       void pm_tell2( FILE *  fileP, pm_filepos * fileposP, unsigned int fileposSize );

       unsigned int pm_tell( FILE * fileP );

       void pm_seek2( FILE *  fileP, const pm_filepos * fileposP, unsigned int fileposSize );

       void pm_seek( FILE *  fileP, unsigned long filepos );

       char *pm_read_unknown_size( FILE * fp, long * nread );

       Description

       An image stream is just a file stream (represented in the standard C library as type FILE *).

       These routines work on files > 2 GiB if the underlying system does, using the standard large file interface.  Before  Netpbm  10.15  (April
       2003), though, they would fail to open any file that large or process any offset in a file that could not be represented in 32 bits.

       pm_openr() opens the given file for reading, with appropriate error checking.  A filename of - is taken to mean Standard Input.	pm_openw()
       opens the given file for writing, with appropriate error checking.  pm_close() closes the file descriptor, with appropriate error checking.

       pm_openr_seekable() appears to open the file just like pm_openr(), but the file thus opened is guaranteed  to  be  seekable  (you  can  use
       ftell() and fseek() on it).  pm_openr_seekable() pulls this off by copying the entire file to a temporary file and giving you the handle of
       the temporary file, if it has to.  If the file you name is a regular file, it's already seekable so pm_openr_seekable() just does the  same
       thing as pm_openr().

       But  if it is, say, a pipe, it isn't seekable.  So pm_openr_seekable() reads the pipe until EOF into a temporary file, then opens that tem-
       porary file and returns the handle of the temporary file.  The temporary file is seekable.

	The file pm_openr_seekable() creates is one that the operating system recognizes as temporary, so when you close the file, by  any  means,
       it gets deleted.

       You  need  a  seekable  file if you intend to make multiple passes through the file.  The only alternative is to read the entire image into
       memory and work from that copy.	That may use too much memory.  Note that the image takes less space in the file cache than in a buffer	in
       memory.	 As much as 96 times less space!  Each sample is an integer in the buffer, which is usually 96 bits.  In the file, a sample may be
       as small as 1 bit and rarely more than 8 bits.

       pm_tell2() returns a handle for the current position of the image stream (file), whether it be the header or a row of the raster.  Use  the
       handle as an argument to pm_seek2() to reposition the file there later.	The file must be seekable (which you can ensure by opening it with
       pm_openr_seekable()) or this may fail.

       The file position handle is of type pm_filepos, which is intended to be opaque, i.e. used only with these two functions.  In  practice,	it
       is  a  file offset and is 32 bits or 64 bits depending upon the capability of the underlying system.  For maximum backward and forward com-
       patibility, the functions that take or return a pm_filepos have a fileposSize argument for the size of the data structure.   In	C,  simply
       code sizeof(pm_filepos) for that.

       pm_seek()  and  pm_tell are for backward compatibility only.  Do not use them in new code.  These functions are not capable of handle posi-
       tions in files whose byte offset cannot be represented in 32 bits.

       pm_tell2() and pm_seek2() replaced pm_tell() and pm_seek() in Netpbm 10.15 (April 2003).

       pm_read_unknown_size() reads an entire file or input stream of unknown size to a buffer.  It allocates more memory as needed.  The  calling
       routine has to free the allocated buffer with free().

       pm_read_unknown_size() returns a pointer to the allocated buffer.  The nread argument returns the number of bytes read.

   Endian I/O
       Entry Points

       void pm_readchar( FILE * in, char * sP );

       void pm_writechar( FILE * out, char s );

       int pm_readbigshort( FILE * in, short * sP );

       int pm_writebigshort( FILE * out, short s );

       int pm_readbiglong( FILE * in, long * lP );

       int pm_writebiglong( FILE * out, long l );

       int pm_readlittleshort( FILE * in, short * sP );

       int pm_writelittleshort( FILE * out, short s );

       int pm_readlittlelong( FILE * in, long * lP );

       int pm_writelittlelong( FILE * out, long l );

       void pm_readcharu( FILE * in, char * sP );

       void pm_writecharu( FILE * out, char s );

       int pm_readbigshortu( FILE * in, short * sP );

       int pm_writebigshortu( FILE * out, short s );

       int pm_readbiglongu( FILE * in, long * lP );

       int pm_writebiglongu( FILE * out, long l );

       int pm_readlittleshortu( FILE * in, short * sP );

       int pm_writelittleshortu( FILE * out, short s );

       int pm_readlittlelongu( FILE * in, long * lP );

       int pm_writelittlelongu( FILE * out, long l );

       Description

       pm_readchar(),	pm_writechar(),   pm_readbigshort(),   pm_writebigshort(),   pm_readbiglong(),	 pm_writebiglong(),  pm_readlittleshort(),
       pm_writelittleshort(), pm_readlittlelong(), and pm_writelittlelong() are routines to read and write 1-byte, 2-byte, and 4-byte pure  binary
       integers  in  either  big- or little-endian byte order.	Note that a 'long int' C type might be wider than 4 bytes, but the 'long' routines
       still read and write 4 bytes.

       pm_readbiglongu(), etc. (names ending in u) are the same except they work on unsigned versions of the type.

       The routines with declared return values always return 0.  Before Netpbm 10.27 (March 2005), they returned -1 on  failure,  including  EOF.
       Now, they issue an error message to Standard Error and abort the program if the I/O fails or encounters EOF.

       The 1-byte routines were new in Netpbm 10.27 (March 2005).  The unsigned versions were new somewhere around Netpbm 10.21 (2004).

   Maxval Arithmetic
       Entry Points

       int pm_maxvaltobits( int maxval );

       int pm_bitstomaxval( int bits );

       unsigned int pm_lcm( unsigned int x, unsigned int y, unsigned int z, unsigned int limit );

       Description

       pm_maxvaltobits() and pm_bitstomaxval() convert between a maxval and the minimum number of bits required to hold it.

       pm_lcm()  computes  the	least  common  multiple  of  3 integers.  You also specify a limit and if the LCM would be higher than that limit,
       pm_lcm() just returns that limit.

   Gamma Arithmetic
       Entry Points

       float pm_gamma709( float intensity );

       float pm_ungamma709( float brightness );

       Description

       In graphics processing, there are two common ways of representing numerically the intensity of a pixel, or a component of a pixel.

       The obvious way is with a number that is directly proportional to the light intensity (e.g. 10 means twice as many  milliwatts  per  square
       centimeter as 5).  There are two problems with this:

       o      To the human eye, a 1 milliwatt per square centimeter difference
		     in a bright image is much less apparent than a 1 milliwatt per
		     square centimeter difference in a dark image.  So if you have
		     a fixed number of bits in which to store the intensity value,
		     you're wasting resolution at the bright end and skimping on it at
		     the dark end.

       o      Monitor inputs and camera outputs aren't directly proportional to
		     the light intensity they project or detect.

       For these reasons, light intensities are often represented in graphics processing by an exponential scale.  The transfer function is called
       a gamma function and the resulting numbers are called gamma-corrected or gamma-adjusted.  There are various gamma  functions.   The  Netpbm
       formats specify that intensities are represented by gamma-adjusted numbers of a particular gamma transfer function.

       These  functions  let  you convert back and forth between these two scales, using the same gamma transfer function that is specified in the
       Netpbm format specifications.

       pm_gamma709 converts from an intensity-proportional intensity value to a gamma-adjusted intensity value (roughly  proportional  to  bright-
       ness, which is the human subjective perception of intensity), using the ITU-R Recommendation BT.709 gamma transfer function.

       pm_ungamma709 is the inverse of pm_gamma709.

   Messages
       Overview

       void pm_message( char * fmt, ... );

       void pm_setusermessagefn(pm_usermessagefn * function);

       Description

       pm_message()  is a printf() style routine to write an informational message to the Standard Error file stream.  pm_message() suppresses the
       message, however, if the user specified the -quiet common option <index.html#commonoptions>  on the command line.  Note	that  Netpbm  pro-
       grams  are often used interactively, but also often used by programs.  In the interactive case, it is nice to issue messages about what the
       program is doing, but in the program case, such messages are usually undesirable.  By using pm_message() for all your  messages,  you  make
       your program usable in both cases.  Without any effort on your part, program users of your program can avoid the messages by specifying the
       -quiet option.

       Netpbm distinguishes between error messages and information messages; pm_message() is just for informational messages.  To issue  an  error
       message, see pm_errormsg() <liberror.html#pm_errormsg> .

       pm_setusermessagefn registers a handler for informational messages, called a user message routine.  Any library function (including pm_mes-
       sage()) that wants to issue an informational message in the future will call that function with the message as an argument instead of writ-
       ing the message to Standard Error.

       The  argument  the  user  message routine gets is English text designed for human reading.  It is just the text of the message; there is no
       attempt at formatting in it (so you won't see any newline or tab characters).

       To capture error messages in addition to informational messages, see pm_setusererrormsgfn() <liberror.html#pm_setusererrormsgfn> .

       You can remove the user message routine, so that the library issues future informational messages in its default  way  (write  to  Standard
       Error) by specifying a null pointer for function.

       Example:

	   static pm_usermessagefn logfilewrite;

	   static void
	   logfilewrite(const char * const msg) {
	       fprintf(mymsglog, 'Netpbm message: %s', msg);
	   }

	   pm_setusermessagefn(&logfilewrite);

	   pm_message('Message for the message log');

   System Utilities
       o

	      pm_system(1)

       o

	      pm_tmpfile(1)

   Keyword Matching
       Entry Points

       void pm_keymatch();

       Description

       This  subroutine is obsolete.  It used to be used for command line option processing.  Today, you can do better option processing more eas-
       ily with the shhopt facility.  See any recent program in the Netpbm package for an example.

       pm_keymatch() does a case-insensitive match of str against keyword.  str can be a leading substring of keyword, but at least minchars  must
       be present.

netpbm documentation						  27 August 2006				    Libnetbpm Utility Functions(3)
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