Custom Exif Tags

Question

I am using exiv2 to manage metadata in a jpeg file. I need to write additional information related to image processing in metadata. Is it possible to create custom Exif tags that are different from the standard ones?

Answer 1

From http://www.exif.org/Exif2-2.PDF :

D. Tags related to user information

Makernote
A tag for Exif file manufacturers to record any desired information. the content is manufacturer-specific, but this tag should not be used for anything other than its purpose.
Tag = 37500 (927C.H)
Type = UNDEFINED
Count = any
Default = none

UserComment
A tag for Exif users to write keywords or comments on an image, except for images in ImageDescription, and without an ImageDescription tag code restriction symbol.
Tag = 37510 (9286.H)
Type = UNDEFINED
Count = any
Default = none

exiv2 supports MakerNote tags: http://dev.exiv2.org/projects/exiv2/wiki/How_to_add_support_for_a_new_makernote

If you do not want to do this, you can use UserComment : http://www.exiv2.org/doc/exifcomment_8cpp-example.html

Answer 2

The best way to create custom metadata is to use Adobe XMP with a custom namespace.

Answer 3

Based on my research, EXIF ​​tags correspond to standard tag sets, as described here .

In the standards document, it indicates (refers to EXIF ​​tags),

A registration system is used for character codes to avoid duplication. When a character code is registered, a standard document is indicated in the reference column to indicate the character format of the specification. If a character code is used for which there is no clear one such as Shift-JIS in Japan, Undefined.

Therefore, his understanding that there is a standard set of tags (registered tags), otherwise, when you request it using a tool such as exiftool, it will display as "Undefined".

So, in order to have a tag recognized by tools or other objects, you need to register your tag in order to become part of standardized tags.