Multipart tiff and EXIF metadata

Question

In the tif format, when you add EXIF meta data it creates an new IFD (tif-direcory) and stores the exif metadata as fields. So when parsing a tif file with a single image and exif data is easy. But you can get multipart tiffs, where a tif can contain more then one image, the question is can each of these images have EXIF data? Does this create a new IFD for each pictures metadata?

What is is the arrangement of the IFD's then?

The tif specification doesn't go into any detail, I know that when a single image tif file has EXIF data there is an offset field to the EXIF data, so I can jump to that location and do the parsing myself, but the Java Sanselan library gives me easy access to the EXIF IFD and fields, but if it is possible to multiple EXIF IFD's (one for each image) then the library doesn't tell me to which image the data belongs.

If you cannot have more then 1 EXIF IFD in a multipart tif file, then it'll be trivial! In other words: Do I need to go to the effort of manually parsing the exif data? Because I only need to do this if you can attach EXIF data to each image inside a multipart tif.

Or does anyone know of a good Linux app that allows me to add EXIF data to tif files so I can figure it out for myself?

Answer 1

To answer your questions:

can each of these images have EXIF data? Does this create a new IFD for each pictures metadata? What is is the arrangement of the IFD's then?

Yes, each of these images can have it's own EXIF data. Each image is related to its own IFD and each EXIF data is a SUB-IFD inside the corresponding image IFD.

but the Java Sanselan library gives me easy access to the EXIF IFD and fields, but if it is possible to multiple EXIF IFD's (one for each image) then the library doesn't tell me to which image the data belongs.

I never used Sanselan and it's successor Apache Imaging so I guess there could be two things happening here: first, Sanselan may by default choose the first page for a multipage TIFF if you actually can insert EXIF to a multipage TIFF; or there might be a parameter which you can set somewhere with a method like setWorkingPage(int page) and this is what I am doing with "icafe" Java image library.

The following is a bit more detailed information as to what is happening inside a TIFF image when you need to add EXIF metadata:

For a single page TIFF, there is a "main" IFD which specifies all the information regarding the image contained there. When EXIF data is needed, an specially tag called "EXIF_SUB_IFD" is added to the main IFD. The value for this tag is an offset address with regards to the image stream start. Now if we jump to the address specified by the offset, we will actually find a "sub" IFD with exactly the same structure as the "main" IFD which contains all the EXIF data.

The above mentioned structure is exactly like a directory tree and hence the name IFD. There is however a subtle difference here: the main IFD should contain the actual image data but the EXIF sub-IFD doesn't. In fact, there is also a GPS sub-IFD which is in parallel with the EXIF sub-IFD and with the same structure as well. An interesting thing is the data for the EXIF can be stored anywhere inside the TIFF image stream (as long as it doesn't break other part of the directory and image data).

Now comes to the multipage TIFF. The pages can be related or not. The last 4 bytes of each page IFD points to the offset of another IFD. They are sometimes gathering together to serve as a "single" document which could be from a scanner. That said, each page is itself a "single" page TIFF which could contain it's own EXIF metadata just like a single page TIFF.

Answer 2

You probably want to check out ExifTool. It works pretty well for what I use it on (JPEGs), but I've never used it with TIFF files containing multiple images. Also check ImageMagick, he has a ton of useful tools.