Re: PNG-EXIF support in exiftool

Hi Cosmin,

Thanks for the feedback.  I will change to use private chunk names as you suggest until the implementation is finalized.  (I much prefer the copy-safe "eXIf" name over the "eXIF" anyway, so I hope it goes this way in the end.)

I believe the zXIF chunk written by ExifTool 10.42 is a valid zlib stream (don't forget to skip the 5-byte header containing the compression type byte and the 4-byte uncompressed length word).  It does have the zlib header (same as ExifTool writes to zTXt).

	- Phil


> On Feb 12, 2017, at 1:02 AM, Cosmin Truta <[email protected]> wrote:
> 
> On 10 February 2017 at 09:09, Phil Harvey <phil-CIeU6mJ2MbMd166Dz3SrqbDks+cytr/[email protected]> wrote:
>> Just FYI in case anyone wants to play with eXIF/zXIF, the latest version of ExifTool supports reading and writing both eXIF and zXIF (add the -z option when writing to create the compressed zXIF):
>> 
>> http://owl.phy.queensu.ca/~phil/exiftool/
> 
> Thanks. I just gave a try to version 10.42, and it does produce the
> new chunks indeed.
> 
> Here are a few observations:
> 
> The compressed ("zXIF") form produced by exiftool does not have a
> valid zlib stream. Maybe it is a deflate stream without the zlib
> stream header? It should have the zlib header, like IDAT, iCCP and
> zTXt do.
> 
> For the uncompressed EXIF chunk at least, the latest draft proposal is here:
> http://www.simplesystems.org/png-group/proposals/eXIf/png-proposed-eXIf-chunk-2017-0210a.html
> 
> One last thing: could you please avoid using any public chunk names
> (like "eXIF" and "zXIF", with second letter in uppercase) until a
> public chunk gets voted in? As mentioned in the draft documents, the
> unregistered name can be used in test implementations, and that name
> is "exIf" for uncompressed, and "zxIf" (or more recently "zxIF") for
> compressed. The second letter should be lowercase.
> 
> Sincerely,
> Cosmin


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