Re: EXIF support in PNG [was: Modern compressor]

On Sat, Dec 31, 2016 at 2:50 PM, John Bowler <
[email protected]> wrote:

> I can't remember what the quorum is, but there should be enough people
> still reading the list for a vote.
>
> I expanded what I said very slightly on the original thread where Glenn
> explained that {Image,Graphics}Magick are currently doing broadly the same
> thing use a zTXt tag and hex encoding.
>

That original thread actually exists in the png-list archives for 2004.
One thing that bothered us was that EXIF can include a thumbnail and we
didn't really want a thumbnail feature.  See
ftp://ftp.simplesystems.org/pub/png-group/archives/png-list.200409



>   The fact that this horrible solution exists and that Cosmin had
> previously implemented the 'raw' proposal is pretty good justification for
> standardization.
>
> I don't know where the authoritative specification of the data is;
> apparently JEITA owns it but ideally there would be a reference to an
> international standard.
>

We don't really need the JEITA spec if we handle it like a black box as we
do with the iCCP chunk.

The format of a proposed eXIf chunk would be similar to that of iCCP:

    keyword (e.g., "Nikon EXIF data", 1-79 bytes of Latin-1 characters)
    null separator
    compression method (0 means zlib/deflate)
    compressed data

Glenn

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