PanoTools Anti Aliasing Filters

Since version 2.7.10 the PanoTools library contains several interpolation filter that avoid aliasing. Those filters use a dynamic kernel size where the size of the filter kernel is calculated for each pixel.

There are two theoretical types of kernels that have an equal right for existence. Kernels based on the Gaussian distribution and kernels based on the Sinc function. Both kernels have an infinite width so a windowing function is used to limit the kernel size for practical reasons. Gaussian based kernels do not contain negative values, sinc based do.

The values in the plot describe the contribution of a pixel depending on the distance from the center. A wider kernel in the center means a more blurry image but if it is to narrow it tends to produce aliasing. If the kernel contains negative values the images also gets sharpened. Some examples: If you look at the plots you can see that a Hamming Filter produces blurrier image then the Blackmann Filter. The Lanczos2 Filter introduces more sharpening then the Mitchell Filter because of the larger negative areas.

short	ID	Name	f(x)	Kernel size
aabox	8	Box Filter		0.5
aatriangle	9	Bartlett/Triangle Filter		1.0
aahermite	10	Hermite Filter		1.0
aahanning	11	Hanning Filter		1.0
aahamming	12	Hamming Filter		1.0
aablackman	13	Blackmann Filter		1.0
aagaussian	14	Gaussian 1/sqrt(2) Filter (blury)		1.25
aagaussian2	15	Gaussian 1/2 Filter (sharper)		1.0
aaquadratic	16	Quadardic Filter		1.5
aacubic	17	Cubic Filter		2.0
aacatrom	18	Catmull-Rom Filter		2.0
aamitchell	19	Mitchell Filter		2.0
aalanczos2	20	Lanczos2 Filter		2.0
aalanczos3	21	Lanczos3 Filter		3.0
aablackmanbessel	22	Blackman/Bessel Filter		3.2383
aablackmansinc	23	Blackman/sinc Filter		4.0

Some examples.