127 lines
4.1 KiB
Groff
127 lines
4.1 KiB
Groff
.TH IM_META 3 "7 June 2005"
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.SH NAME
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im_meta_set_int, im_meta_get_int, im_meta_set_double, im_meta_get_double,
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im_meta_set_area, im_meta_get_area, im_meta_set_string, im_meta_get_string,
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im_meta_set_blob, im_meta_get_blob,
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im_meta_set, im_meta_get
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\- read and write extra header fields
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.SH SYNOPSIS
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#include <vips/vips.h>
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int im_meta_set_int( IMAGE *im, const char *field, int i );
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.br
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int im_meta_get_int( IMAGE *im, const char *field, int *i );
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.br
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int im_meta_set_double( IMAGE *im, const char *field, double d );
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.br
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int im_meta_get_double( IMAGE *im, const char *field, double *d );
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.br
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int im_meta_set_area( IMAGE *im, const char *field,
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im_callback_fn free_fn, void *data );
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.br
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int im_meta_get_area( IMAGE *im, const char *field, void **data );
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.br
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int im_meta_set_string( IMAGE *im, const char *field,
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const char *str );
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.br
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int im_meta_get_string( IMAGE *im, const char *field, char **str );
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.br
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int im_meta_set_blob( IMAGE *im, const char *field,
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im_callback_fn free_fn, void *blob, size_t blob_length );
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.br
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int im_meta_get_blob( IMAGE *im, const char *field,
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void **blob, size_t *blob_length );
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typedef int (*im_callback_fn)( void *, void * );
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int im_meta_set( IMAGE *im, const char *field, GValue *value );
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.br
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int im_meta_get( IMAGE *im, const char *field, GValue *value_copy );
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.br
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GType im_meta_get_type( IMAGE *im, const char *field );
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#define IM_TYPE_SAVE_STRING (im_save_string_get_type())
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.br
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GType im_save_string_get_type( void );
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.br
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const char *im_save_string_get( const GValue *value );
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.br
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void im_save_string_set( GValue *value, const char *str );
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.br
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void im_save_string_setf( GValue *value, const char *fmt, ... );
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.SH DESCRIPTION
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These functions read and write extra image header fields. Writing to a field
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destroys any old value. You must read a field with the correct type of reader:
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you can't read an int field as a string. Fields are copied when images are
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processed, so you can use them to pass information to subsequent operations.
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Unless otherwise noted, image header fields created with these functions are
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also saved to disc when an image is saved in VIPS format, and automatically
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restored when the image is loaded again.
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.B im_meta_set_int(3)
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sets an integer field. Any existing field of any type with this name is
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removed. It returns 0 for success, or -1 on error setting
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.B im_error(3).
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.B im_meta_get_int(3)
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reads an integer field. It returns 0 for success, or -1 on error, setting
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.B im_error(3).
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It can fail if the field does not exist, or if the field is not an int.
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.B im_meta_set_double(3)
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and
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.B im_meta_get_double(3)
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work exactly as
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.B im_meta_set_int(3)
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and
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.B im_meta_get_int(3).
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.B im_meta_set_area(3)
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sets a field which is an area of memory. When the field is copied to a
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subsequent IMAGE, VIPS just copies the pointer. VIPS keeps a reference count
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and when the last IMAGE using this field is closed, VIPS will call
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.B free_fn
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to release the memory. You can therefore use this function to attach very
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large areas of memory to images efficiently. Areas cannot be saved to VIPS
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files on disc, since there is no known length.
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.B im_meta_set_string(3)
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is a convenience function over
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.B im_meta_set_area(3).
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It copies the string, and
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then shares that copy between all images derived from this IMAGE.
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.B im_meta_get_string(3)
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is a convenience function over
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.B im_meta_get_area(3).
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It returns a pointer to the string being mananged by VIPS. Do not free the
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return result!
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.B im_meta_set_blob(3)
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sets a field which is a blob (binary object). A blob is just like string,
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except that rather than being NULL-terminated, you must pass an explicit
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length.
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.B im_meta_set(3),
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.B im_meta_get_type(3)
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and
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.B im_meta_get(3)
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operate at a lower level: they let you set image header fields as GValue. Use
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one of the convenience functions above if possible.
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.B im_meta_get_type(3)
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returns 0 if the field is not defined.
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In order for the autoload/save to VIPS files to work, you need to use a GType
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with a transform defined to and from
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.B IM_TYPE_SAVE_STRING.
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.SH RETURN VALUE
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The functions return 0 success and -1 on error.
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.SH SEE ALSO
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im_header_int(3), im_header_map(3).
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.SH COPYRIGHT
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The National Gallery, 2005.
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.SH AUTHOR
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Markus Wollgarten and John Cupitt
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