[gdal-dev] Question on 0th IFD offset when producing a JPEG-Compressed GeoTIFF (GDAL 1.11 vs 2.x)
daniele.romagnoli at geo-solutions.it
Fri Dec 16 05:56:50 PST 2016
On Fri, Dec 16, 2016 at 2:48 PM, Even Rouault <even.rouault at spatialys.com>
> > 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
> > the output overviews were jpeg compressed (I assume there is some kind of
> > coherency check in gdaladdo).
> With internal overviews, the _OVERVIEW configuration options are ignored.
> Their value is deduced from the settings of the main IFD.
It makes sense, indeed.
> I don't think there's a strong technical reason for that. Mostly a side
> effect of the fact that there are slightly different code paths to handle
> creation of internal and external overviews, and the reading of _OVERVIEW
> config options is done only in the external overview code path.
> > > I do reproduce something similar to your findings in 2.1 indeed. This
> > > 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?
> No API change, but this is in the improvement category rather than
> bugfixing, and my first changeset resulted in some corrupted images in some
> situations, which was unnoticed for a few weeks, so that's a sign that it
> is a somewhat risky change (the GeoTIFF driver is a complex beast), not
> worth the trouble of breaking stable branches.
Understood. thanks for the feedback.
> Spatialys - Geospatial professional services
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