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

[Seth Price]

The only way to 'force' it is to use cubicspline or lanczos. Everything
else has a hardcoded filter size. If those are too slow, I'd suggest using
the OpenCL code I wrote over the summer. It's many times faster. (It
should be in trunk soon if it isn't already.)

http://github.com/mailseth/OpenCL-integration-for-GRASS---GDAL

~Seth



On Wed, September 29, 2010 4:12 pm, Craig de Stigter wrote:
> Thanks Even
>
> However if I do the same thing with reprojection I get the same result.
> gdalwarp output looks sharp and ugly, imagemagick output looks nice.
>
> Is there any way to force the bilinear/cubic interpolation to notice more
> pixels? The other interpolation methods are much slower, I imagine even
> forcing cubic to notice all of the 5x5 pixels would still be faster.
>
> Regards
> Craig de Stigter
>
> On Thu, Sep 30, 2010 at 10:34 AM, Even Rouault
> <even.rouault at mines-paris.org
>> wrote:
>
>> 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
>>
>
>
>
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