## header

header — get, set and walk image headers

## Stability Level

Stable, unless otherwise indicated

## Synopsis

    #include <vips/vips.h>

    #define             VIPS_META_EXIF_NAME
    #define             VIPS_META_XMP_NAME
    #define             VIPS_META_IPCT_NAME
    #define             VIPS_META_ICC_NAME
    #define             VIPS_META_XML
    #define             VIPS_META_RESOLUTION_UNIT
    #define             VIPS_META_LOADER
    guint64             vips_format_sizeof                  (VipsBandFormat format);
    int                 vips_image_get_width                (const VipsImage *image);
    int                 vips_image_get_height               (const VipsImage *image);
    int                 vips_image_get_bands                (const VipsImage *image);
    VipsBandFormat      vips_image_get_format               (const VipsImage *image);
    VipsCoding          vips_image_get_coding               (const VipsImage *image);
    VipsInterpretation  vips_image_get_interpretation       (const VipsImage *image);
    VipsInterpretation  vips_image_guess_interpretation     (const VipsImage *image);
    double              vips_image_get_xres                 (const VipsImage *image);
    double              vips_image_get_yres                 (const VipsImage *image);
    int                 vips_image_get_xoffset              (const VipsImage *image);
    int                 vips_image_get_yoffset              (const VipsImage *image);
    const char *        vips_image_get_filename             (const VipsImage *image);
    const char *        vips_image_get_mode                 (const VipsImage *image);
    double              vips_image_get_scale                (const VipsImage *array);
    double              vips_image_get_offset               (const VipsImage *array);
    void *              vips_image_get_data                 (VipsImage *image);
    void                vips_image_init_fields              (VipsImage *image,
                                                             int xsize,
                                                             int ysize,
                                                             int bands,
                                                             VipsBandFormat format,
                                                             VipsCoding coding,
                                                             VipsInterpretation interpretation,
                                                             double xres,
                                                             double yres);
    void                vips_image_set                      (VipsImage *image,
                                                             const char *field,
                                                             GValue *value);
    int                 vips_image_get                      (const VipsImage *image,
                                                             const char *field,
                                                             GValue *value_copy);
    int                 vips_image_get_as_string            (const VipsImage *image,
                                                             const char *field,
                                                             char **out);
    GType               vips_image_get_typeof               (const VipsImage *image,
                                                             const char *field);
    gboolean            vips_image_remove                   (VipsImage *image,
                                                             const char *field);
    void *              (*VipsImageMapFn)                   (VipsImage *image,
                                                             const char *field,
                                                             GValue *value,
                                                             void *a);
    void *              vips_image_map                      (VipsImage *image,
                                                             VipsImageMapFn fn,
                                                             void *a);
    void                vips_image_set_area                 (VipsImage *image,
                                                             const char *field,
                                                             VipsCallbackFn free_fn,
                                                             void *data);
    int                 vips_image_get_area                 (const VipsImage *image,
                                                             const char *field,
                                                             void **data);
    void                vips_image_set_blob                 (VipsImage *image,
                                                             const char *field,
                                                             VipsCallbackFn free_fn,
                                                             void *data,
                                                             size_t length);
    int                 vips_image_get_blob                 (const VipsImage *image,
                                                             const char *field,
                                                             void **data,
                                                             size_t *length);
    int                 vips_image_get_int                  (const VipsImage *image,
                                                             const char *field,
                                                             int *out);
    void                vips_image_set_int                  (VipsImage *image,
                                                             const char *field,
                                                             int i);
    int                 vips_image_get_double               (const VipsImage *image,
                                                             const char *field,
                                                             double *out);
    void                vips_image_set_double               (VipsImage *image,
                                                             const char *field,
                                                             double d);
    int                 vips_image_get_string               (const VipsImage *image,
                                                             const char *field,
                                                             const char **out);
    void                vips_image_set_string               (VipsImage *image,
                                                             const char *field,
                                                             const char *str);
    int                 vips_image_history_printf           (VipsImage *image,
                                                             const char *format,
                                                             ...);
    int                 vips_image_history_args             (VipsImage *image,
                                                             const char *name,
                                                             int argc,
                                                             char *argv[]);
    const char *        vips_image_get_history              (VipsImage *image);

## Description

These functions let you get at image header data (including metadata) in a uniform way. They are handy for language bindings but less useful for C users.

They first search the VIPS header fields (see image), then search for a metadata field of that name (see meta). Use `vips_image_get_typeof()` to test for the existance and GType of a header field.

See meta for a set of functions for adding new metadata to an image.

## Details

### VIPS_META_EXIF_NAME

    #define VIPS_META_EXIF_NAME "exif-data"

The name that JPEG read and write operations use for the image's EXIF data.

### VIPS_META_XMP_NAME

    #define VIPS_META_XMP_NAME "xmp-data"

The name that JPEG read and write operations use for the image's XMP data.

### VIPS_META_IPCT_NAME

    #define VIPS_META_IPCT_NAME "ipct-data"

The name that JPEG read and write operations use for the image's IPCT data.

### VIPS_META_ICC_NAME

    #define VIPS_META_ICC_NAME "icc-profile-data"

The name we use to attach an ICC profile. The file read and write operations for TIFF, JPEG, PNG and others use this item of metadata to attach and save ICC profiles. The profile is updated by the `vips_icc_transform()` operations.

### VIPS_META_XML

    #define VIPS_META_XML "xml-header"

The original XML that was used to code the metadata after reading a VIPS format file.

### VIPS_META_RESOLUTION_UNIT

    #define VIPS_META_RESOLUTION_UNIT "resolution-unit"

The JPEG and TIFF read and write operations use this to record the file's preferred unit for resolution.

### VIPS_META_LOADER

    #define VIPS_META_LOADER "vips-loader"

Record the name of the original loader here. Handy for hinting file formats and for debugging.

### vips_format_sizeof ()

    guint64             vips_format_sizeof                  (VipsBandFormat format);

### vips_image_get_width ()

    int                 vips_image_get_width                (const VipsImage *image);

### vips_image_get_height ()

    int                 vips_image_get_height               (const VipsImage *image);

### vips_image_get_bands ()

    int                 vips_image_get_bands                (const VipsImage *image);

### vips_image_get_format ()

    VipsBandFormat      vips_image_get_format               (const VipsImage *image);

### vips_image_get_coding ()

    VipsCoding          vips_image_get_coding               (const VipsImage *image);

### vips_image_get_interpretation ()

    VipsInterpretation  vips_image_get_interpretation       (const VipsImage *image);

### vips_image_guess_interpretation ()

    VipsInterpretation  vips_image_guess_interpretation     (const VipsImage *image);

### vips_image_get_xres ()

    double              vips_image_get_xres                 (const VipsImage *image);

### vips_image_get_yres ()

    double              vips_image_get_yres                 (const VipsImage *image);

### vips_image_get_xoffset ()

    int                 vips_image_get_xoffset              (const VipsImage *image);

### vips_image_get_yoffset ()

    int                 vips_image_get_yoffset              (const VipsImage *image);

### vips_image_get_filename ()

    const char *        vips_image_get_filename             (const VipsImage *image);

### vips_image_get_mode ()

    const char *        vips_image_get_mode                 (const VipsImage *image);

### vips_image_get_scale ()

    double              vips_image_get_scale                (const VipsImage *array);

### vips_image_get_offset ()

    double              vips_image_get_offset               (const VipsImage *array);

### vips_image_get_data ()

    void *              vips_image_get_data                 (VipsImage *image);

Return a pointer to the image's pixel data, if possible. This can involve allocating large amounts of memory and performing a long computation. Image pixels are laid out in band-packed rows.

See also: `vips_image_wio_input()`.

`image` : | image to get data for
Returns : | a pointer to pixel data, if possible.

### vips_image_init_fields ()

    void                vips_image_init_fields              (VipsImage *image,
                                                             int xsize,
                                                             int ysize,
                                                             int bands,
                                                             VipsBandFormat format,
                                                             VipsCoding coding,
                                                             VipsInterpretation interpretation,
                                                             double xres,
                                                             double yres);

A convenience function to set the header fields after creating an image. Normally you copy the fields from your input images with `vips_image_pipelinev()` and then make any adjustments you need, but if you are creating an image from scratch, for example `im_black()` or `im_jpeg2vips()`, you do need to set all the fields yourself.

See also: `vips_image_pipelinev()`.

`image` : | image to init
`xsize` : | image width
`ysize` : | image height
`bands` : | image bands
`format` : | band format
`coding` : | image coding
`interpretation` : | image type
`xres` : | horizontal resolution, pixels per millimetre
`yres` : | vertical resolution, pixels per millimetre

### vips_image_set ()

    void                vips_image_set                      (VipsImage *image,
                                                             const char *field,
                                                             GValue *value);

Set a piece of metadata on `image`. Any old metadata with that name is destroyed. The GValue is copied into the image, so you need to unset the value when you're done with it.

For example, to set an integer on an image (though you would use the convenience function `vips_image_set_int()` in practice), you would need:

    GValue value = { 0 };

    g_value_init( &value, G_TYPE_INT );
    g_value_set_int( &value, 42 );
    vips_image_set( image, field, &value );
    g_value_unset( &value );

    return( 0 );

See also: `vips_image_get()`.

`image` : | image to set the metadata on
`field` : | the name to give the metadata
`value` : | the GValue to copy into the image

### vips_image_get ()

    int                 vips_image_get                      (const VipsImage *image,
                                                             const char *field,
                                                             GValue *value_copy);

Fill `value_copy` with a copy of the header field. `value_copy` must be zeroed but uninitialised.

This will return -1 and add a message to the error buffer if the field does not exist. Use `vips_image_get_typeof()` to test for the existence of a field first if you are not certain it will be there.

For example, to read a double from an image (though of course you would use `vips_image_get_double()` in practice):

    GValue value = { 0 };
    double d;

    if( vips_image_get( image, field, &value ) )
      return( -1 );

    if( G_VALUE_TYPE( &value ) != G_TYPE_DOUBLE ) {
      vips_error( "mydomain",
        _( "field \"%s\" is of type %s, not double" ),
        field,
        g_type_name( G_VALUE_TYPE( &value ) ) );
      g_value_unset( &value );
      return( -1 );
    }

    d = g_value_get_double( &value );
    g_value_unset( &value );

    return( 0 );

See also: `vips_image_get_typeof()`, `vips_image_get_double()`.

`image` : | image to get the field from from
`field` : | the name to give the metadata
`value_copy` : | the GValue is copied into this
Returns : | 0 on success, -1 otherwise.

### vips_image_get_as_string ()

    int                 vips_image_get_as_string            (const VipsImage *image,
                                                             const char *field,
                                                             char **out);

Gets `out` from `im` under the name `field`. This function will read any field, returning it as a printable string. You need to free the string with `g_free()` when you are done with it.

See also: `vips_image_get()`, `vips_image_get_typeof()`.

`image` : | image to get the header field from
`field` : | field name
`out` : | return field value as string
Returns : | 0 on success, -1 otherwise.

### vips_image_get_typeof ()

    GType               vips_image_get_typeof               (const VipsImage *image,
                                                             const char *field);

Read the GType for a header field. Returns zero if there is no field of that name.

See also: `vips_image_get()`.

`image` : | image to test
`field` : | the name to search for
Returns : | the GType of the field, or zero if there is no field of that name.

### vips_image_remove ()

    gboolean            vips_image_remove                   (VipsImage *image,
                                                             const char *field);

Find and remove an item of metadata. Return `FALSE` if no metadata of that name was found.

See also: `vips_image_set()`, `vips_image_get_typeof()`.

`image` : | image to test
`field` : | the name to search for
Returns : | `TRUE` if an item of metadata of that name was found and removed

### VipsImageMapFn ()

    void *              (*VipsImageMapFn)                   (VipsImage *image,
                                                             const char *field,
                                                             GValue *value,
                                                             void *a);

### vips_image_map ()

    void *              vips_image_map                      (VipsImage *image,
                                                             VipsImageMapFn fn,
                                                             void *a);

This function calls `fn` for every header field, including every item of metadata.

Like all _map functions, the user function should return `NULL` to continue iteration, or a non-`NULL` pointer to indicate early termination.

See also: `vips_image_get_typeof()`, `vips_image_get()`.

`image` : | image to map over
`fn` : | function to call for each header field
`a` : | user data for function
Returns : | `NULL` on success, the failing pointer otherwise.

### vips_image_set_area ()

    void                vips_image_set_area                 (VipsImage *image,
                                                             const char *field,
                                                             VipsCallbackFn free_fn,
                                                             void *data);

Attaches `data` as a metadata item on `image` under the name `field`. When VIPS no longer needs the metadata, it will be freed with `free_fn`.

See also: `vips_image_get_double()`, `vips_image_set()`

`image` : | image to attach the metadata to
`field` : | metadata name
`free_fn` : | free function for `data`. [scope async]
`data` : | pointer to area of memory

### vips_image_get_area ()

    int                 vips_image_get_area                 (const VipsImage *image,
                                                             const char *field,
                                                             void **data);

Gets `data` from `image` under the name `field`. A convenience function over `vips_image_get()`. Use `vips_image_get_typeof()` to test for the existance of a piece of metadata.

See also: `vips_image_set_area()`, `vips_image_get()`, `vips_image_get_typeof()`

`image` : | image to get the metadata from
`field` : | metadata name
`data` : | return metadata value
Returns : | 0 on success, -1 otherwise.

### vips_image_set_blob ()

    void                vips_image_set_blob                 (VipsImage *image,
                                                             const char *field,
                                                             VipsCallbackFn free_fn,
                                                             void *data,
                                                             size_t length);

Attaches `blob` as a metadata item on `image` under the name `field`. A convenience function over `vips_image_set()` using an vips_blob.

See also: `vips_image_get_blob()`, `vips_image_set()`.

`image` : | image to attach the metadata to
`field` : | metadata name
`free_fn` : | free function for `data`. [scope async]
`data` : | pointer to area of memory
`length` : | length of memory area

### vips_image_get_blob ()

    int                 vips_image_get_blob                 (const VipsImage *image,
                                                             const char *field,
                                                             void **data,
                                                             size_t *length);

Gets `blob` from `image` under the name `field`, optionally return its length in `length`. A convenience function over `vips_image_get()`. Use `vips_image_get_typeof()` to test for the existance of a piece of metadata.

See also: `vips_image_get()`, `vips_image_get_typeof()`, `vips_blob_get()`,

`image` : | image to get the metadata from
`field` : | metadata name
`data` : | pointer to area of memory
`length` : | return the blob length here, optionally
Returns : | 0 on success, -1 otherwise.

### vips_image_get_int ()

    int                 vips_image_get_int                  (const VipsImage *image,
                                                             const char *field,
                                                             int *out);

Gets `out` from `im` under the name `field`. This function searches for int-valued fields.

See also: `vips_image_get()`, `vips_image_get_typeof()`

`image` : | image to get the header field from
`field` : | field name
`out` : | return field value
Returns : | 0 on success, -1 otherwise.

### vips_image_set_int ()

    void                vips_image_set_int                  (VipsImage *image,
                                                             const char *field,
                                                             int i);

Attaches `i` as a metadata item on `image` under the name `field`. A convenience function over `vips_image_set()`.

See also: `vips_image_get_int()`, `vips_image_set()`

`image` : | image to attach the metadata to
`field` : | metadata name
`i` : | metadata value

### vips_image_get_double ()

    int                 vips_image_get_double               (const VipsImage *image,
                                                             const char *field,
                                                             double *out);

Gets `out` from `im` under the name `field`. This function searches for double-valued fields.

See also: `vips_image_get()`, `vips_image_get_typeof()`

`image` : | image to get the header field from
`field` : | field name
`out` : | return field value
Returns : | 0 on success, -1 otherwise.

### vips_image_set_double ()

    void                vips_image_set_double               (VipsImage *image,
                                                             const char *field,
                                                             double d);

Attaches `d` as a metadata item on `image` under the name `field`. A convenience function over `vips_image_set()`.

See also: `vips_image_get_double()`, `vips_image_set()`

`image` : | image to attach the metadata to
`field` : | metadata name
`d` : | metadata value

### vips_image_get_string ()

    int                 vips_image_get_string               (const VipsImage *image,
                                                             const char *field,
                                                             const char **out);

Gets `out` from `im` under the name `field`. This function searches for string-valued fields.

Do not free `out`.

See also: `vips_image_get()`, `vips_image_get_typeof()`

`image` : | image to get the header field from
`field` : | field name
`out` : | return field value
Returns : | 0 on success, -1 otherwise.

### vips_image_set_string ()

    void                vips_image_set_string               (VipsImage *image,
                                                             const char *field,
                                                             const char *str);

Attaches `str` as a metadata item on `image` under the name `field`. A convenience function over `vips_image_set()` using an vips_ref_string.

See also: `vips_image_get_double()`, `vips_image_set()`, vips_ref_string

`image` : | image to attach the metadata to
`field` : | metadata name
`str` : | metadata value

### vips_image_history_printf ()

    int                 vips_image_history_printf           (VipsImage *image,
                                                             const char *format,
                                                             ...);

Add a line to the image history. The `format` and arguments are expanded, the date and time is appended prefixed with a hash character, and the whole string is appended to the image history and terminated with a newline.

For example:

    vips_image_history_printf( image, "vips im_invert %s %s",
      in->filename, out->filename );

Might add the string

    "vips im_invert /home/john/fred.v /home/john/jim.v # Fri Apr  3 23:30:35
    2009\n"

VIPS operations don't add history lines for you because a single action at the application level might involve many VIPS operations. History must be recorded by the application.

`image` : | add history line to this image
`format` : | printf() format string
Returns : | 0 on success, -1 on error.

### vips_image_history_args ()

    int                 vips_image_history_args             (VipsImage *image,
                                                             const char *name,
                                                             int argc,
                                                             char *argv[]);

Formats the name/argv as a single string and calls `vips_image_history_printf()`. A convenience function for command-line prorams.

See also: `vips_image_get_history()`.

`image` : | image to attach history line to
`name` : | program name
`argc` : | number of program arguments
`argv` : | program arguments
Returns : | 0 on success, -1 on error.

### vips_image_get_history ()

    const char *        vips_image_get_history              (VipsImage *image);

This function reads the image history as a C string. The string is owned by VIPS and must not be freed.

VIPS tracks the history of each image, that is, the sequence of operations that generated that image. Applications built on VIPS need to call `vips_image_history_printf()` for each action they perform, setting the command-line equivalent for the action.

See also: `vips_image_history_printf()`.

`image` : | get history from here
Returns : | The history of `image` as a C string. Do not free!

## See Also

meta, check