Some format filters, such as EXIF-JPEG, EXIF-TIFF, TIFF, JPEG, PNG and some others contain non-image data, generally referred to as metadata. ImageGear provides a mechanism for reading the metadata during image loading and modifying it during image saving. Non-image data itself can be of any possible complex type, depending on the nature of the file format. ImageGear processes this complex data through a single interface and allows uniform processing that does not depend on the actual data format, and starts from information fields of such simple formats as BMP and PCX, up to the complex metadata support in the EXIF filter and the IPTC non-image data format in such filters as TIFF and JPEG.

While EXIF-JPEG and EXIF-TIFF are separate image file formats using JPEG or TIFF image data compressions, IPTC is a format used only for non-image data storage in such imaging format filters as JPEG and TIFF. For more detailed information about these formats, see the EXIF-TIFF Non-Image Data Structure, EXIF-JPEG Non-image Data Structure, and the IPTC Non-Image Data Structure sections in Appendix: Non-Image Data Storage as well as the EXIF-JPEG and EXIF-TIFF sections in the File Format Reference.

ImageGear is responsible for translating this format-dependent data into a standard uniform format. There are at least two operations that include such data processing:

• Image loading - during image loading, some additional data needs to be loaded and uncompressed into the set of values of standard types for further processing.
• Image saving - during image saving, there should be a way to change existing defined values and add new values.

This section provides the following information:

• Non-Image Data Format
• Using Filter Callback Functions to Process Non-Image Data
• Updating Non-Image Data without Loading and Saving the Image
• Working with XMP Metadata