Re: DRAFT: eXIf 2017-03-02

On 7 March 2017 at 00:11, Pavel Zlatovratskii wrote:
> One step at time: what benefit in preview in IFD[1] in comparison to
> separate preview chunk?

The IFD1 preview is not a purpose in itself, but a secondary
by-product of importing the EXIF design. We adopt it in order to stay
compliant to the EXIF design. Implementors may or may not find a
benefit in it. We should not the break the IFD1 apart, regardless.

A thumbnail image in a publicly-registered PNG chunk was discussed in
the early stages of PNG development (more than 20 years ago), and yet
it was rejected. I wasn't a forum member at that time, but the
discussion archives still exist. I agree that it was a bad idea back
then (and the correct decision has been made), and I still consider it
to be a bad idea now. This is a closed chapter, from my point of view.

> Developer of camera firmware already have to handle PNG chunk structure
> for eXIf chunk, there should be no problem to add extra chunk. But this
> extra chunk could be added even before eXIf that makes more freedom in
> design firmware.

The EXIF structure is monolithic. The existing hardware and software
is not necessarily prepared to handle an EXIF structure broken apart,
especially because nobody else breaks it. Special circuitry (or
circuitry updates) may be necessary for the change that you're
suggesting, and we should not require any of that.

I repeat what I had said before: all of the other non-TIFF image
formats that are EXIF containers (JPEG/WebP/JPEG-2000/BPG/etc/etc)
happen to have a tagged structure, just like PNG; and yet, none of
them break the EXIF apart. Neither should we.

Sincerely,
Cosmin

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