[ptx] Comparison of different interpolation functions.

[Bruno Postle]

On Wed 11-May-2005 at 03:53 -0700, Michael Norel wrote:

> Comparison of different interpolation functions. 
> 
> http://www.minorlogic.com/projects/interpolation/index.htm

Very interesting.

Your test was to scale up and down repeatedly, which is going to
cause problems with interpolators that don't do 'downsizing' very
well such as spline/bicubic.

Another test would be to try non-scaling interpolation, ie. rotate
an image 1 degree at a time for 360 iterations.

There is a problem very specific to panoramas, you might have some
insight:

Panorama Tools is useless for scaling an image down since all the
interpolators available are of the 'bicubic' type and produce
aliased pixel output.

This is generally ok, since if you want smaller output then the
large image can be scaled with something like ImageMagick that uses
Lanczos sampling when downsizing.

Where it isn't ok is when sampling an equirectangular panorama.  Due
to the extreme distortion at the top and bottom of an
equirectangular image, sampling a group of pixels can be effectively
both scaling up and scaling down at the same time - It would be
interesting to see if some of the other filters are any better at
dealing with this.

-- 
Bruno