Exif support

[seaeagle1]

Curious whether this is (or can be turned into) something usable for more than just me.

I've added a way to access embedded Exif tags in a sort-of-standardized way. The basic idea is that allows access when decoding images for other parsing libraries and for recoding images with the Exif tag intact. Since Exif is essentially TIFF-formatted, all the basic tools were more or less in place and I just had to tweak them a bit. The things that were really missing was support for IFD sub-directories and encoding values with a dynamically derived type.

Decoder -> has a method to gather the Exif information, store the entries and feed them into an encoder for a TIFF-file without pixel data.

Encoder -> has a similar method to decode TIFF-file with-or-without pixel data and feed the Exif entries into the encoder itself.

[fintelia]

Thanks for sharing this!

I've been wanting to add better EXIF handling to image-rs and being able to convert the EXIF data in a TIFF file into the same form as the EXIF chunks in PNG or JPEG would certainly help with that. It'll probably be a little while before I have a chance to work on implementing that, so I'll leave this open for now