TYPES AND CONSTANTS¶

Each gray should contain only the values between 0 and PGM_OVERALLMAXVAL. pgm_pbmmaxval is the maxval used when a PGM program reads a PBM file. Normally it is 1; however, for some programs, a larger value gives better results.

PGM_OVERALLMAXVAL is the maximum value of a maxval in a PGM file. PGM_MAXMAXVAL is the maximum value of a maxval in a PGM file that is compatible with the PGM format as it existed before April 2000. It is also the maximum value of a maxval that results in the minimum possible raster size for a particular image. I.e an image with a maxval higher than PGM_MAXMAXVAL cannot be read or generated by old PGM processing programs and requires more file space.

PGM_FORMAT is the format code for a Plain PGM format image file. RPGM_FORMAT is the format code for a Raw PGM format image file. PGM_TYPE is the format type code for the PGM formats. PGM_FORMAT_TYPE is a macro that generates code to compute the format type code of a PBM or PGM format from the format code which is its argument.

INITIALIZATION¶

All PGM programs must call pgm_init() just after invocation, before they process their arguments.

MEMORY MANAGEMENT¶

pgm_allocarray() allocates an array of grays.

pgm_allocrow() allocates a row of the given number of grays.

pgm_freearray() frees the array allocated with pgm_allocarray() containing the given number of rows.

pgm_freerow() frees a row of grays allocated with pgm_allocrow().

READING FILES¶

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

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

pgm_readpgmrow() reads a row of grays into the grayrow array. format, cols, and maxval are the values returned by pgm_readpgminit().

pgm_readpgm() reads an entire PGM 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 pgm_readpgminit(), pgm_allocarray(), and pgm_readpgmrow().

WRITING FILES¶

pgm_writepgminit() writes the header for a PGM file and leaves it positioned just after the header.

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

pgm_writepgmrow() writes the row grayrow to a PGM file. For meaningful results, cols, maxval, and forceplain must be the same as was used with pgm_writepgminit().

pgm_writepgm() write the header and all data for a PGM image. This function combines pgm_writepgminit() and pgm_writepgmrow().

MISCELLANEOUS¶

pgm_nextimage() positions a PGM input file to the next image in it (so that a subsequent pgm_readpgminit() reads its header).

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

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

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