[gdal-dev] Question on 0th IFD offset when producing a JPEG-Compressed GeoTIFF (GDAL 1.11 vs 2.x)

Daniele Romagnoli daniele.romagnoli at geo-solutions.it
Fri Dec 16 05:29:10 PST 2016


On Fri, Dec 16, 2016 at 1:52 PM, Even Rouault <even.rouault at spatialys.com>
wrote:

>
>
> > Wondering if when generating overviews we still have a problem similar to
>
> > the one you have fixed in 2.0 or some data-updating issue.
>
> >
>
> > These are my hypothesis on what is going on.
>
> > A simple translate with no overviews makes the file ending at 0x7555 with
>
> > offset of next IFD saying 0x0000.
>
> > When you add overviews, it writes a new IFD at 0x7556 with TAG entries,
>
> > then it encodes something and then it writes a new IFD.
>
> > At the end, it goes back updating the offset of the 1st overview IFD
>
> > (0xBBF0) making the one at 0x7556 being not referred anymore.
>
> > Does it make sense?
>
> >
>
>
>
> With JPEG compression right ?
>
Right,
Indeed, before sending my previous email I have also tried with:
*gdaladdo -r average --config COMPRESS_OVERVIEW DEFLATE --config
PHOTOMETRIC_OVERVIEW RGB*
to understand if it was related to JPEG only but, even with these options,
the output overviews were jpeg compressed (I assume there is some kind of
coherency check in gdaladdo).



> I do reproduce something similar to your findings in 2.1 indeed. This no
> longer happens in trunk due to related improvements (
> https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF), I made in the
> last couple of weeks (using the same trick of creating a in-memory TIFF
> file to get the JPEG tables and set them direcly on the overview IFD at
> creation time).
>
>
>
Do you think this will be available in other series or does it introduce
new API/major changes which makes it available on 2.2.x only?
Thanks again for your precious feedbacks.

Cheers,
Daniele


> Even
>
>
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>



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