Re: DRAFT: eXIF 2017-05-28

On Wed, May 31, 2017 at 4:00 PM, Pavel Zlatovratskii <[email protected]> wrote:
>
>
> 31.05.2017 15:52, Glenn Randers-Pehrson пишет:
>>
>>
>>> So no simple PNG-to-EXIF conversion will be allowed for eXIf (I still
>>> doubt
>>> that such conversion could be simple enough for eXIF).
>>
>> If the image data has been changed.  It is safe to do that when the image
>> has not changed.  I would expect all of the Exif profile to survive a
>> simple
>> JPEG -> PNG -> JPEG round trip, although it would not bother me if
>> the JPEG-specific data were to be lost.
>
> In most practical cases you simply don't know if image has been changed or
> not.
>
> It is one simple way in PNG: if chunk is unsafe to copy. But it is subject
> of discussion: how to make EXIF chunk safe to copy.

Yes, we all know that.  The problem here is that Exif contains valuable
safe-to-copy information and worthless unsafe-to-copy information, and
we want to preserve the former.  We could do that be defining an eXIf
chunk that only contains the safe-to-copy fields, but that involves
decoders having to understand the Exif profile enough to be able
to separate the good from the bad.

I think the explanations in the current eXIf draft are sufficient.

Glenn

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