Re: Endless gamma in eXIf 2017-0119

I've been looking at the Exif specification to see what it says
about editor behavior.

See CIPA DC-008-translation-2012 (follow link in our proposal)

Paragraph E.3 is the relevant part.

In essence there are many tags that contain historical
information about the camera that should be copied; however,
there are some that should be updated.  From the PNG
point of view, that means there are copy-safe tags and
copy-unsafe tags.

As I have observed with ImageMagick, we can't depend upon
applications properly updating the Exif profile, no matter how
it is stored (PNG chunk, Exif tags in a JPEG, etc.).

One possibility would be for PNG to define two chunks:
eXIf to contain the copy-safe tags (camera information)
and eXIF to contain the copy-unsafe tags (image information).

It's not KISS, but it should work.  Applications that don't
or won't update the Exif data when editing an image would
automatically discard the unsafe eXIF but keep the safe eXIf
chunk.  Applications that originally create a PNG could
put everything in eXIF if they don't want to be bothered
with separating them.

Glenn

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