On Sat, 30 Aug 2008 19:35:20 +0200, Alastair M. Robinson  

>  Comparing Lanczos 3% old vs patched: lefthand building roof has bad  
> moire  effects that totally obscure underlying detail. Both sets of  
> trees have  much less obvious staircasing in the current code. There is  
> an overall  impression of sharpness in the new code but this seems  
> really to be just  high contrast artifacts with a lack of intermediate  
> tones.
>  I think these are aliasing artifacts caused by high-frequency  
> components in the original image - unless you take steps to remove  
> frequencies higher than the target sample rate before resampling a  
> signal, aliasing will result.  And as you noted, it affects my code too.

That's exactly what lanczos does. Which is why you don't see any alising  
and you get smooth transitions. Whether the overall softness of the image  
is correct rendition and a neccessary feature or due to some minor errors  
in calculating the kernel may be worth looking at.

If the code is close but not quite right some softening would be likely.



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