Re: CFD: eXIf 2017-06-09a

After reviewing old mailing-list archives, I've added a couple
of names (Brendan Bolles and Michael Stokes) to the contributors list.

The first proposal for this chunk in almost its current form was
by me in July 2000 (only differing in its being copy-unsafe eXIF,
and not specifying whether the Exif\0\0 bytes are included).

Back then, I wrote:

"I was initially considering embedding the entire TIFF-EP directory
in a new eXIF chunk, a la EXIF/JPEG.  There are a couple of problems
with that, one being that it would have to be copy-unsafe and therefore
will likely be discarded.  Also a lot of the info seems to be genuinely
useful, so pulling it out into a human-readable, standard PNG text chunk
that apps already know how to process makes more sense.  The data
includes a lot of baggage that is of no use once the image has been
converted into another format (JPEG Qtables, TIFF tiling and stripping
info, etc.) and is just wasted space if saved.  Once you decide not
to save that at all, hardly any of the remaining info is not copy-safe,
especially if we identify it as "original width, orientation, etc." and
not simply "width, orientation, etc.""

and Adam wrote

"However, notice that this digicam meta-info standard began as extensions
to TIFF, and when they wanted to store the info in JFIF files, they
didn't make up something new in the spirit of JFIF, they simply embedded
a TIFF-EP file in the JFIF file.  That suggests that we should at
least consider the option of embedding the same TIFF-EP file in a PNG
chunk.  It's quick-and-dirty, but would make it easy for people to reuse
code, and make it trivial for PNG to track the evolution of the EXIF
standard.  And if the main purpose of having this info in the PNG file
is for putting the image back into the camera, this would save having to
translate the info and then translate it back.  Note that this wouldn't
be the first time we've done something like this--witness iCCP and gIFx.

"On the other hand, if any of the meta-info defined by EXIF is generally
useful for applications other than digital cameras, it would be a shame
to trap it inside such a complex chunk.  We should consider whether any
of that meta-info deserves being separated out into new general-purpose
chunks."

I sincerely hope we can finish this discussion and achieve a
sucdessful vote before July 2020.

Glenn

On Fri, Jun 9, 2017 at 8:56 AM, Glenn Randers-Pehrson <[email protected]> wrote:

>> Have a look at the 2017-06-09b version.
>> Glenn

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