.TH IM_HEADER 3 "7 May 2002"
.SH NAME
im_header_int, im_header_double, im_header_string, im_header_get,
im_header_get_type, im_header_map \- read fields from the image header
.SH SYNOPSIS
#include <vips/vips.h>

int im_header_int( IMAGE *image, const char *field, int *out )
.br
int im_header_double( IMAGE *image, const char *field, double *out )
.br
int im_header_string( IMAGE *image, const char *field, char **out )
.br
GType im_header_get_type( IMAGE *im, const char *field );
.br
int im_header_get( IMAGE *im, const char *field, GValue *value_copy );
.br
typedef void *(*im_header_map_fn)( IMAGE *,
  const char *, GValue *, void *, void * );
.br
void *im_header_map( IMAGE *im, 
  im_header_map_fn fn, void *a, void *b );

.SH DESCRIPTION
.B im_header_int(3)
reads the value of an integer header field. These are
"Xsize", "Ysize", "Bands", "Bbits", "BandFmt", "Coding", and "Type", or any
integer meta field.

.B im_header_double(3)
reads the value of the integer header fields. These are
"Xres", and "Yres", or any double meta field.

.B im_header_string(3)
reads the value of the integer header fields. These are
"Hist", and "filename" or any string meta field. 

.B im_header_get_type(3)
returns the GType (eg. G_TYPE_INT) for a field. It returns zero if the field
does not exist. It does not set 
.B im_error(3),
so it's useful for test for a field's existence.

.B im_header_get(3)
fills the GValue with a copy of the field value, if the field exists. The
value should be zeroed but otherwise uninitialised. The value should be unset
once the user has finished with it.

.B im_header_map(3)
maps a function over all header fields, presenting the value of each field as
a GValue. Return non-NULL from the map function to stop iteration early. It
maps over the builtin fields first, then any meta fields.

.SH RETURN VALUE
All functions returns 0 on success and -1 on error.
.SH SEE ALSO
im_close(3), im_open(3).