[gdal-dev] Fwd: Add overviews there is a difference between interleave

[Even Rouault]

On mardi 8 janvier 2019 17:21:43 CET Guy Doulberg wrote:
> Hi guys
> 
> I am trying to fix artifacts that the gdaladdo is creating in the overview
> I am working on.
> 
> The gdal version I am working with is 2.3.2
> 
> In general I have a big vrt file (RGB) on top of COGs with internal masks.
> There are places in the original rasters that we mask the values.
> 
> 
> But when building overviews it seems like that the masked values in some
> layers are used, and artifacts are being created.
> 
> I was trying to play with many variant to understand these artifacts
> creation, the only variant I noticed to have an impact is the INTERLEAVE of
> the overviews,
> 
> When I set it to PIXEL it runs fast but creates artifacts
> When I set it to BAND it runs 3 times longer and there are less artifacts
> created.
> 
> So far my understanding of the INTERLEAVE configuration was that it affects
> the final products block arrangement, I don't understand why it affects the
> product values, and the processing time as well

Normally the interleaving configuration shouldn't have impacts, unless you use 
a lossy compression in which case the way data is written might have some 
influence. So what you observe is a bug/feature of GDAL not using the same 
code paths internally in the PIXEL case where multi-band processing is done, 
and in the BAND case where bands are processed independantly. Both methods 
normally takes into account source masks, but the code is substantially 
different so there is likely some subtelty occuring here.
The processing time is dependant of those different code paths, as well as the 
interleaving of the source band from which the overviews are created.

Even

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