libvips/man/VipsFormat.3

.TH VIPS_FORMAT 3 "16 August 2008"
.SH NAME
VipsFormat, 
vips_format_map, vips_format_for_file, vips_format_for_name, 
vips_format_write \- 
load and search image formats
.SH SYNOPSIS
#include <vips/vips.h>

typedef enum {
.br
  VIPS_FORMAT_NONE = 0,
.br
  VIPS_FORMAT_PARTIAL = 1
.br
} VipsFormatFlags;

typedef struct _VipsFormatClass {
.br
  VipsObjectClass parent_class;

  gboolean (*is_a)( const char * );
.br
  int (*header)( const char *, IMAGE * );
.br
  int (*load)( const char *, IMAGE * );
.br
  int (*save)( IMAGE *, const char * );
.br
  VipsFormatFlags (*get_flags)( const char * );
.br
  int priority;
.br
  const char **suffs;
.br
} VipsFormatClass;

void *vips_format_map( VSListMap2Fn fn, void *a, void *b );
.br
VipsFormatClass *vips_format_for_file( const char *filename );
.br
VipsFormatClass *vips_format_for_name( const char *filename );

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

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

.SH DESCRIPTION
These functions search the 
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. On the other hand, this format API is useful for 
controlling how a image
is unpacked, since you can specify a destination for the copy.

Image formats are subclasses of
.B VipsFormat
as outlined above. They are expected to implement at least one of the methods.
They should also set values for the
.B nickname
and 
.B description
members of 
.B VipsObject.

Other members are:

.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 load method implemented.

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

.B priority
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 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 vips_format_map(3)
maps a function over the list of available formats. See 
.B im_slist_map(3).

.B vips_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 vips_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 vips_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 vips_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