Namespaces

The Exiv2 library is made up of all

elements defined in the Exiv2

namespace.

Classes

The top-level class of the Exiv2 library is 

href="classExiv2_1_1Image.html">Exiv2::Image.  Exiv2::Image

defines the interface to access image metadata.  Derived from

Exiv2::Image are implementations for different image formats. Most

importantly, they contain the logic to read metadata from the image

into Exiv2 metadata containers and write it back to the image.

Most applications will use

Exiv2::ImageFactory 

to access images in files or memory, in which case the image format 

is transparent to them. The factory determines the image format from the

data (not the file extension) and creates an object of the corresponding

Image subclass.

Exif and IPTC metadata is manipulated through the classes

Exiv2::ExifData 

and Exiv2::IptcData.

They hold a container of Exif and IPTC metadata, respectively, and define

related methods to access and manipulate the metadata.

Exif tag and IPTC dataset reference information for the standard tags

and datasets is available in the two static classes

Exiv2::ExifTags and

Exiv2::IptcDataSets.

The metadata containers hold objects derived from

Exiv2::Metadatum.

Interface class Exiv2::Metadatum defines methods to access the

information of one metadatum. It models the tag data as a key and

value pair.

The abstract base class 

Exiv2::Key defines the 

interface for a key. Concrete keys implement Exif and IPTC keys.

The abstract base class 

Exiv2::Value defines 

the interface to access tag information, from which concrete values are

derived. The actual value used in a metadatum depends on the type of

the Exif tag or IPTC dataset. It is usually determined when the Exif or

IPTC metadata is read from an image. It is also possible to manually create

a Value and together with a key add it to an ExifData or IptcData 

container.

The classes to access XMP metadata are 

Exiv2::XmpData,

Exiv2::Xmpdatum 

and Exiv2::XmpKey.

They work similar to the corresponding Exif and IPTC classes.

The property reference information is in

Exiv2::XmpProperties.

In addition to the expected new members, class

Exiv2::Image

now also has an interface to access the raw XMP packet.

All XMP value types are supported: Simple types, structures,

arrays, property qualifiers and language alternatives.

XMP properties are accessed through keys of the form

"Xmp.<Prefix>.<PropertyPath>", where <Prefix> is the preferred 

(or rather, registered) prefix for a schema namespace and 

<PropertyPath> is the path of the XMP node. In its most basic

form, to address simple properties, <PropertyPath> is the name

of the property. In general, <PropertyPath> can be used to 

address any XMP node, including array items, structure fields

qualifiers and deeply nested properties.

Any properties in known namespaces are supported and additional

namespaces can be registered.

The specialized Exiv2 values 

Exiv2::XmpTextValue,

Exiv2::XmpArrayValue

and Exiv2::LangAltValue are

provided to simplify the use of XMP properties.

Note: Unlike Exif and IPTC tags, XMP properties do not have

a tag number.

Examples

There are several simple examples that demonstrate the basic use of Exiv2

functionality: Exifprint 

shows how the Exif data of an image can be read and written to the screen.

Iptcprint is a similar 

example to print IPTC data.

Addmoddel shows how to

add, modify and delete Exif metadata. 

Exifcomment shows how to

set the exif comment of an image. 

Xmpsample.cpp contains examples

of how to set various types of XMP properties.

For more real-world code have a look at the implementation of the

different actions of the Exiv2 utility (actions.cpp).

Makernotes

Exif Makernote data can be accessed through ExifData in the same

way as the standard Exif tags. In other words, for each entry of a

known Makernote, there is a corresponding Metadatum in the ExifData

container. Makernote taglists are internally kept in classes

Exiv2::Internal::<Make>MakerNote (e.g.,

Exiv2::Internal::CanonMakerNote.)