>From a cursory websearch it looks like this is not possible in the standard
APP1 segment normally used for XMP data. You should be able to use
multiple APP2 segments which i believe are also used for ICC profile data
(which are usually >64K). Some sample code I found is here:
http://src.chromium.org/svn/trunk/src/third_party/iccjpeg/iccjpeg.c
On Wed, Sep 25, 2013 at 9:33 PM, Ulrich Pegelow <ulrich.pege...@tongareva.de
> wrote:
> Hi guys,
>
> this is a request for support to XMP/EXIF experts.
>
> Let me describe the issue: when exporting images we store the complete
> history stack as XMP-tags in the exported file - i.e. if the file format
> supports tagging. The nice thing here is the ability to recover the whole
> development process even in case the sidecar file gets lost. All you need
> is the raw and an exported image.
>
> This used to work fine with "normal" history stacks. Now we have masks.
> These masks, although efficiently stored in vector format, can consume a
> quite significant number of kbytes. In case of complicated history stacks
> we now can easily exceed the available segment size for XMP tags. In the
> case of JPEGs this is 64k.
>
> darktable produces an error message like:
>
> [xmp_attach] caught exiv2 exception 'Size of XMP JPEG segment is larger
> than 65535 bytes'
> [imageio_storage_disk] could not attach xmp data to file:
> `/home/pegelow/Bilder/**Testbilder/darktable_exported/**
> IMG_6371x_0001_17.jpg'!
>
> Still the JPEG file gets exported and is usable. However, it has lost the
> history stack.
>
> To my understanding JPEG supports a way to split XMP tags over multiple
> segments. So, there should in principle be on option to overcome this issue.
>
> Would be great if someone could take care of this topic.
>
> Attached you find an example of a huge history stack which causes problems.
>
> Ulrich
>
>
>
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--
Psychogios Dimitrios,
IT Systems Specialist
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