Re: DRAFT: eXIf 2017-02-28

How about:

While the PNG specification allows the chunk size to be as large as
2^31-1 bytes, encoders should be aware that, if the Exif profile is
converted to JPEG, the total length of the Exif data (the sum of the
lengths of the Exif attributes IFD, the GPS IFD, the thumbnail IFD, and
the TIFF header) must not exceed 64 kbytes, because it must fit into
a JPEG APP1 marker.

?

Glenn


On Thu, Mar 2, 2017 at 11:53 AM, John Bowler
<[email protected]> wrote:
> The section seems clear to me; the reference is to the format of the
> *data*, not the format of the *chunk* (PNG) or the *marker* (JPEG).
> Indeed, IRC, CIPA points out that JPEG (not CIPA/EXIF) limits the
> length to 64k.
>
> Since this is the only example, so far as I know, of EXIF embedded in
> a foreign file format the reference is useful.  I think we have to
> assume that the reader of the PNG spec will appreciate that references
> to JPEG specific items in that section have to be interpreted with
> respect to the corresponding features in PNG.
>
> John Bowler
>
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