Re: CFD: zXIF 2017-0207

As I have already stated in my "yes" vote for eXIf, I would not
support an unsafe-to-copy form in any incarnation.

The whole point of the EXIF proposal is to preserve the EXIF
information. Preservation of significant EXIF information (most
importantly, camera info, lens info, exposure info) across
applications is highly important to digital photography applications
and to many, many users.

If PNG adopts an unsafe-to-copy chunk for EXIF, it becomes itself an
unsafe container for EXIF. This automatically implies the following
advice to users: "use TIFF instead of PNG if EXIF is important to
you".

The EXIF structure has hundreds of safe-to-copy fields, many of which
are highly significant; and two unsafe-to-copy fields (thumbnail and
preview image), both of which are redundant and therefore
informationally insignificant.

Any application that recognizes thumbnails and previews may (and
probably should) regenerate them at any time, as instructed by the
specification; or may even drop them, just as it may drop any other
EXIF fields not applicable to PNG (such as, for example, JPEG-only
fields).

I believe that adoption for PNG in the area of digital photography
cannot happen if the important photographic information is preserved.
What exactly should make photographers switch from TIFF to PNG?
Deflate-compressed TIFF has been working just fine. Even uncompressed
TIFF (where compression is not important) is equally fine. Load any
TIFF/EXIF, process it, save it, and see how the metadata info
(including EXIF) is kept reliably.

PNG/EXIF cannot possibly compete with TIFF/EXIF in the marketplace,
unless the EXIF chunk inside PNG is safe-to-copy.

Sincerely,
Cosmin

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