Re: Endless gamma in eXIf 2017-0119

On Tue, Feb 7, 2017 at 10:21 PM, John Bowler <
[email protected]> wrote:

> On Tue, Feb 7, 2017 at 7:32 PM, Glenn Randers-Pehrson <[email protected]>
> wrote:
> > I suggest three things.
> >
> > 1: make the chunk unsafe-to-copy,
>
> Yes.
>
> > 2. remove the Security Considerations paragraph from
> > the eXIf proposal (but keep the other part of Security considerations
> > about uncontrolled expansion in the zXIf proposal, and
>
> Yes
>
> > 3. include the following three paragraphs:
>
> These paragraphs are too open ended for a spec; they reflect the
> conclusions I came to but they are wishy-washy.
>
> The following is a bit long but these are the conclusions I came to
> today (nothing like driving 200 miles through severe weather warnings
> to give you time to think :-)
>
> The normative part of a specification needs to contain direct,
> unambiguous, yet minimal directives for a conforming implementation.
> This is possible.  Recommendations for decoders, transcoders, encoders
> and editors may be helpful but are informative, not normative.
> Rationales are something that happens on this list or in an appendix
> ;-)
>

I'm OK with moving most of the stuff in the 3 paragraphs into the
"Recommendations for Decoders" section.

A simple rule for decoders removes that requirement so that a
> transcoder can copy the original EXIF verbatim.


The 0207 draft allows that.

Making it copy-unsafe takes care of a lot of potential inadvertent
errors (at the cost of discarding the Exif data)

We still need some complex explanation of what an editor
that recognizes eXIF/zXIF is supposed to do when it makes
changes to the image that would render it copy-unsafe, to
make it permissible to write a new Exif profile.  I think that
what they need to do is adequately explained in the
Exif spec, Annex E, so maybe all we need to do is make
reference to that (which the 0207 drafts do).

Glenn

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