Re: Fwd: VOTE ABSTAIN: eXIf 2017-0119

On Tue, Feb 7, 2017 at 10:08 AM, Willem van Schaik <[email protected]>
wrote:

>
> would it be enough to add a statement that "when information in the EXIF
> chunk is in contradiction with information in any other chunk, it should
> be ignored"
>
> Willem
>

No, for reasons explained by Pavel.  It can be in contradiction with
gamma information that has been removed.

I do think the chunk proposal can be salvaged with a additional statement,
but it has to be more than that sentence.

I'm thinking that the specification should tell decoders that they
must ignore any "editable" tags such as gamma (i.e., any tag
that the Exif spec paragraph E.3 does not say "should be copied
unchanged").

We have to allow encoders to write those tags,
for simplicity, but we don't want decoders to use those potentially
invalid tags to be used in reconstructing a new Exif profile.

Fortunately many of those are also covered by other PNG
chunks (resolution, modification date/time, gamma) and many
others (dealing with the image compression, etc.) are of no
use when the pixel format changes from JPEG or TIFF
to PNG.  There are a few that aren't, though, and I'm
not sure how to handle those (subject location, orientation,
processing instructions).

Glenn

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