libvips/man/VipsFormat..3

.TH IM_FORMAT 3 "16 August 2008"
.SH NAME
im_format_register, im_format_set_priority, im_format_unregister,
im_format_map, im_format_for_file, im_format_for_name, im_format_write \- 
load and search image formats
.SH SYNOPSIS
#include <vips/vips.h>

typedef enum {
.br
  IM_FORMAT_FLAG_NONE = 0,
.br
  IM_FORMAT_FLAG_PARTIAL = 1
.br
} im_format_flags;

typedef gboolean (*im_format_is_a_fn)( const char * );
.br
typedef int (*im_format_header_fn)( const char *, IMAGE * );
.br
typedef int (*im_format_load_fn)( const char *, IMAGE * );
.br
typedef int (*im_format_save_fn)( IMAGE *, const char * );
.br
typedef im_format_flags (*im_format_flags_fn)( const char * );

typedef struct im__format_t {
.br
  const char *name;
.br
  const char *name_user;
.br
  int priority;        
.br
  const char **suffs; 
.br
  im_format_is_a_fn is_a;
.br
  im_format_header_fn header;
.br
  im_format_load_fn load;
.br
  im_format_save_fn save;
.br
  im_format_flags_fn flags;
.br
} im_format_t;

im_format_t *im_format_register(
.br
  const char *name, const char *name_user, const char **suffs,
.br
  im_format_is_a_fn is_a, im_format_header_fn header,
.br
  im_format_load_fn load, im_format_save_fn save,
.br
  im_format_flags_fn flags );
.br
void im_format_set_priority( im_format_t *format, int priority );
.br
void im_format_unregister( im_format_t *format );

void *im_format_map( VSListMap2Fn fn, void *a, void *b );
.br
im_format_t *im_format_for_file( const char *filename );
.br
im_format_t *im_format_for_name( const char *filename );

int im_format_write( IMAGE *im, const char *filename );

int im_format_read( const char *filename, IMAGE *out );

.SH DESCRIPTION
These functions register and unregister image formats, and search the table of 
available image formats to find one suitable for loading or saving a file.

.B im_open(3) 
will do something similar, but that returns a descriptor to the file rather
than copying to a descriptor you supply. 

The two APIs are useful in different circumstances: 
.B im_open(3) 
is good if you want to directly manipulate a file on disc, for example with
the paintbox functions. The format API is useful for controlling how a image
is unpacked, since you can specify a destination for the copy.

.B im_format_register(3)
registers an image format with vips. This might typically be called during
module load, see the documentation for GModule.

An image format has a number of components:

.B name
The internal name by which the format should be known. For example, the 
OpenEXR image format is known within vips as "exr". You can identify formats
by testing this field with 
.B strcmp(3).

.B name_user
The name as it should be displayed to the user. It can be internationalised.
For example, in English, the "analyze" format is shown as "Analyze 6.0".

.B suffs
A NULL-terminated array of possible file-name suffixes for this format. This
list is used to filter filenames when they are shown to the user, and to help
select a format to sav a file as. For example, the JPEG format has the
suffixes:
.B { ".jpg", ".jpeg", ".jpe", NULL }

.B is_a
A function which tests whether a file is of the specified format. This is
useful if you can guess a file type from the first few bytes in the file. If
you leave this function NULL, vips will guess from the filename suffix for
you.

.B header
Load only the image header, not any of the image pixels. vips will call this
first on
.B im_open(3)
and delay loading pixels until asked. If you leave this NULL, vips will just
use the 
.B load 
function.

.B load
Load the image from the file into the IMAGE. You can leave this function NULL
if you only have a 
.B save
method implemented.

.B save
Write from the IMAGE to the file in this format. You can leave this function
NULL if you only have a lload method implemented.

.B flags
A function which examines the file and sets various flags to indicated
properties of the image. The only flag implemented at the moment is
.B IM_FORMAT_FLAG_PARTIAL
which may be set to indicate that the file can be read lazily.

vips registers the format and returns a pointer to the
.B im_format_t 
it created. This may later be used to unregister the format.

.B im_format_set_priority(3)
sets a priority for the format. Priorities for formats default to zero: you
mmay set a lower or higher number to set where in the format table your format
is positioned. 

.B im_format_unregister(3)
removes a format from vips. It mmight typically be called during module
unload, see the documentation for GModule.

.B im_format_map(3)
maps a function over the list of loaded formats. See 
.B im_slist_map(3).

.B im_format_for_file(3)
looks at a file on disc and selects the 'best' format to use to load that 
file. If no suitable format is found, it returns NULL and sets an error
message.

.B im_format_for_name(3)
looks at a filename and picks a format to use to save that file based on the
file extension. If no suitable format is found, it returns NULL and sets an
error message.

.B im_format_read(3)
is a convenience function which copies the image from the file into the IMAGE. 
error, it returns non-zero and sets an error message.

.B im_format_write(3)
is a convenience function which copies the image to the file in the
appropriate format. On error, it returns non-zero and sets an error message.

.SH RETURN VALUE
The functions return 0 success and -1 on error.
.SH SEE ALSO
im_tiff2vips(3), im_open(3).
.SH AUTHOR
Jesper Friis and John Cupitt