[gdal-dev] Downscaled geotiff with overviews

[Even Rouault]

If you initialize empty overviews ( BuildOverviews("NONE", ... ) ), then 
you can read the downscaled version of the original geotiff and put that 
in the target overviews. Of course you'll pay the price of 
decompression/recompression. By using directly the libtiff API, you 
could save that

Even

Le 30/07/2021 à 20:19, Javier Jimenez Shaw a écrit :
> Hi
>
> I want to make a (power-of-two) downscaled version of a geotiff with 
> overviews efficiently with C++ (not from the console).
>
> Let's say I have a geotiff with overviews (external or internal), and 
> I want a copy of it, but at 50% of the size. That is just removing the 
> "base" of the pyramid, but keeping all the other levels. Then voilà, 
> there you have the geotiff 50% smaller, with the overviews already 
> there, almost without any computation. The same for 25% (and any power 
> of 2).
>
> However I do not figure out how to do it efficiently in C++. If I 
> understand correctly, CreateCopy is producing an image with the same 
> size. So to downscale I have to create a new image, read downscaled 
> (that will use the overviews) and write. But later, I have to recreate 
> the overviews on the new image... that are already in the original image.
>
> Is there any way to make it efficiently? (as we have the data there)
>
> Thanks.
> .___ ._ ..._ .. . ._. .___ .. __ . _. . __..  ... .... ._ .__
> Entre dos pensamientos racionales
> hay infinitos pensamientos irracionales.
>
>
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