rawler: access all EXIF tags of a raw file

[RReverser]

I'm parsing CR3 files and, among others, need to extract FocalPlaneYResolution.

When I parse it using decode_file(...), the dng_tags field remains unpopulated - I guess it's format-dependant and is only filled for DNG images.

So then I found I can retrieve global decoder and invoke raw_metadata(...) on the file, which is more cumbersome, but at least actually parses the metadata from CR3. Unfortunately, the returned metadata is limited to only some well-known fields and doesn't contain what I need.

Is there any way to get raw list of all tags instead, so that I could extract what I need by EXIF number myself? Maybe dng_tags could be populated for any format upon decoding?

[cytrinox]

Access to raw IFDs is problematic, as in newer formats like CR3 there is no "root IFD". In CR3, EXIF tags are spread over CMT1, CMT2 and CMT3 boxes, each forming a separate root IFD.

The recommended solution is to just extend all tags defined by EXIF standard here:

dnglab/rawler/src/exif.rs

Line 160 in 7f6ee5a

(ExifTag::LensSerialNumber, Value::Ascii(data)) => self.lens_serial_number = data.strings().get(0).map(trim),

Then the requested EXIF attribute can be simply accessed via raw_metadata().

I would be happy reviewing a PR for this 😉

[RReverser]

Access to raw IFDs is problematic, as in newer formats like CR3 there is no "root IFD". In CR3, EXIF tags are spread over CMT1, CMT2 and CMT3 boxes, each forming a separate root IFD.

Yeah I don't need raw IFDs, just raw EXIF values, even if it's after merging all EXIF data from all IFDs.

That in, in the linked branch it could collect any unknown values into a separate HashMap<u16, Value>. That doesn't solve the issue of not getting this info right in dng_tags upon decode_image, but at least provides some way to access the data.

[cytrinox]

This should be possible now as IFDs are now accessible #412