[gdal-dev] cubic / bilinear resampling with gdalwarp looks similar to nearest neighbour

[Even Rouault]

Craig,

The main reason is that you are using gdalwarp to reduce an image by a large 
factor and not reproject it, which generally only involves image resizing by 
small factors. The implementation of the bilinear and cubic resampling 
algorithms is currently not designed for the pure resizing use case and takes 
only into account a few source pixels (basically if to compute a destination 
pixel you would need to take into account a 5x5 source window, they will only 
used the 4 corners of that square, which fine usually since those are just the 
immediate neighbours of the source pixel), whereas cubicspline and lancsoz 
take into account more pixels (all the pixels in the 5x5 square).

Best regards,

Even

Le mercredi 29 septembre 2010 22:27:01, Craig de Stigter a écrit :
> Hi folks
> 
> I filed this bug <http://trac.osgeo.org/gdal/ticket/3740> on gdal a few
> weeks back and haven't heard anything since.
> 
> Would someone mind taking a look at it?
> 
> Thanks
> Craig de Stigter