Re: Blackman interpolation instead of linear or cubic

By Kaba:

Here's an example. You can do _perfect_ low pass filtering in the
Fourier sense by taking the discrete fourier transform, then multiplying
by a box mask and taking the inverse discrete fourier transform. This
corresponds to convoluting with a sinc filter with an infinite support.
Let's do that.

This doesn't work perfectly if the data are not band-limited below the
Nyquist frequency.

Image data are never band-limited. A pixel sequence black-white-
black ..
consists only of a Nyquist frequency component and a DC part (gray).
Any real world image contains signals with Nyquist frequency.
Fourier transforms create artifacts if the spectrum isn't strictly
band-
limited.

The Blackman window function isn't very different to windows by
von Hann, Hamming or Lanczos. Interpreted as a filter, the rejection
band is below (about) -60dB, but this interpretation is only half the
truth. One has to test the pulse response in the time domain.

I have actually added 'Blackman' to an older doc:
http://www.fho-emden.de/~hoffmann/lanczos07112002.pdf

Best regards --Gernot Hoffmann




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