Re: CALL for DISCUSSION: eXIf 20170115

On Thu, Jan 19, 2017 at 10:58 AM, Jason Summers <[email protected]> wrote:
> Sorry if I missed something, but as far as I can tell, the plan is still to
> put a JPEG app ID string (or "Exif ID code" as they call it in ExifLand)
> ("Exif\0\0") in PNG files.
>
> I think that's a bad idea. The JPEG app ID string is a JPEG-specific thing
> that doesn't belong in other formats.

It needs to be there in the private (i.e. exIf) to distinguish it from
other private chunks of the same name; the TIFF header isn't really
enough.  We could remove it from the public one, that is the way it
has been done in the past.  The reason I didn't was because the
existing implementation of EXIF in PNG preserves it.

I haven't seen a justification for this; the existing implementation
uses a text chunk with a readily identifiable string.  Nevertheless,
it is there.

It does make more sense to me to skip it but there may be a good reason for it.

The second '\0' is described as "padding" in the translated CIPA
document and I have seen it set to something other than \0, something
may have been lost in the translation.  When I first saw a non-zero
value it looked like a version number for the EXIF spec but I suspect
it was just a mistake.  I don't see any harm in *not* having it.

-- 
John Bowler <[email protected]>
+1 (541) 450-9885
PO BOX 3151
KERBY OR 97531-3151
USA

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