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libvips supports getting and setting image header data (including metadata) in a uniform way.

Use vips_image_get_typeof() to test for the existence and GType of a header field.

You can attach arbitrary metadata to images. Metadata is copied as images are processed, so all images which used this image as input, directly or indirectly, will have this same bit of metadata attached to them. Copying is implemented with reference-counted pointers, so it is efficient, even for large items of data. This does however mean that metadata items need to be immutable. Metadata is handy for things like ICC profiles or EXIF data.

Various convenience functions (e.g. vips_image_set_int()) let you easily attach simple types like numbers, strings and memory blocks to images. Use vips_image_map() to loop over an image’s fields, including all metadata.

Items of metadata are identified by strings. Some strings are reserved, for example the ICC profile for an image is known by convention as “icc-profile-data” (i.e. the VIPS_META_ICC_NAME constant).

If you save an image in .v format, all metadata (with a restriction, see below) is automatically saved for you in a block of XML at the end of the file. When you load a .v image, the metadata is restored. You can use the vipsedit command-line tool to extract or replace this block of XML.

.v metadata is based on GValue. See the docs for that system if you want to do fancy stuff such as defining a new metadata type. libvips defines a new GValue called VipsSaveString, a variety of string, see vips_value_set_save_string(). If your GValue can be transformed to VipsSaveString, it will be saved and loaded to and from .v files for you.

libvips provides a couple of base classes which implement reference-counted areas of memory. If you base your metadata on one of these types, it can be copied between images efficiently.

Callbacks

Functions

Constants