[COG] Mixed Raw and Overview data compression ?

Even Rouault even.rouault at spatialys.com
Tue Sep 18 07:56:30 PDT 2018

On mardi 18 septembre 2018 14:45:49 CEST Pfister, Marc wrote:
> On Sun, 16 Sep 2018 20:39:32 -0400 Vincent Sarago <vincent.sarago at gmail.com> 
> > JPEG (or WEBP) compression are great for storage saving (and also for
> > small http request) but they are `bad` because they are not lossless
> > (WEBP can be set to be lossless but compression is then not as great) so
> > my idea is to package both lossless and non-lossless in one COG. e.g
> > keeping high resolution data to a ZSTD/DEFLATE compression but the
> > overview in JPEG.
> Setting aside the issues of bit depth, can the current tools (namely GDAL)
> handle mixed compression types?

It should have no issue in reading a COG with mixed compression types.
But it cannot currently generate a GeoTIFF with different compression types 
for full resolution imagery and overviews. There are no particular fundamental 
obstacles to do it if it had to be implemented.

> I've also been pondering how far can you "abuse" the concept of overviews
> with different compression, bit depth, band combinations, and so on. So I
> am interested to see how this works out even at a basic level.

GDAL will require all overview levels to have identical band count and bit 


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