[gdal-dev] Remove Black Areas From Rotated Images

[M Lewis]

Thanks Even

I am assuming that even in doing this there may still be an issue with
differentiating between pixels of pure black and this 0 'no-data' value in
an 8 bit band where raster min gives 0 and raster max gives 255.....ah well.

There is another question and I have noticed that the dataset created from
AutoCreateWarpedVRT has different raster min and max values.

One of the rasters (a single UInt16 band, rotated) has a raster min of 337.0
and a raster max of 872.0 when computed using ComputeRasterMinMax().

However the AutoCreateWarpedVRT dataset created from this original dataset
has a min of 0.0 and a max of 772.0, why?????

My plan (using your idea) of setting the no-data value to 0.0 would work on
the original dataset as the minimum is > 0.0 and therefore 0.0 could be
filtered out; however due to the conversion by the AutoCreateWarpedVRT, 0.0
is now a valid colour and once again falls into the issue of whether 0.0 is
'no-data' or a genuine colour.

Thanks

Martin



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