anti-aliasing filters?

[kgross]

Hi,

I've seen some discussions on this forum about anti-aliasing, but I haven't found an answer to my question and I'd appreciate any input.

Does anybody know at what frequency anti-aliasing filters are designed to cut at? Is the cut frequency just below or above the grey-scale Nyquist frequency or is it just above or below the bayer Nyquist frequency?

Thanks
Kevin

[AJSJones]

Hi,

I've seen some discussions on this forum about anti-aliasing, but I haven't found an answer to my question and I'd appreciate any input.

Does anybody know at what frequency anti-aliasing filters are designed to cut at? Is the cut frequency just below or above the grey-scale Nyquist frequency or is it just above or below the bayer Nyquist frequency?

Thanks
Kevin
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Can't answer your question as posed, but you might be able to do the optics/maths.

 The following image came from a Canon document (my link expired) where the shift for each LPF was stated as " one pixel up and one pixel left".  The 4 point images would now each be at ~25% of the original photon flux and each point would go to four sensor elements, presumably ensuring that a sensor element of each color recorded some information about the original point source, as required to minimize color moire.  



[a href=\"http://www.sensor-film.com/filter.html]Actual images[/url] of AA filters are consistent with Canon changing the thickness of the lithium niobate layers in the AA filter assembly in proportion to the pixel spacing to maintain the 1 pixel shift, but whether it is actually 1.0 pixel is unknown!  

Andy

[kgross]

Andy,

Assuming that the birefringent crystal is the same material in the 5D and the 20D it might be possible to figure it out. A math problem for tomorrow when I'm not so sleepy.

Thanks for your input.
Kevin

Can't answer your question as posed, but you might be able to do the optics/maths.

 The following image came from a Canon document (my link expired) where the shift for each LPF was stated as " one pixel up and one pixel left".  The 4 point images would now each be at ~25% of the original photon flux and each point would go to four sensor elements, presumably ensuring that a sensor element of each color recorded some information about the original point source, as required to minimize color moire. 



Actual images of AA filters are consistent with Canon changing the thickness of the lithium niobate layers in the AA filter assembly in proportion to the pixel spacing to maintain the 1 pixel shift, but whether it is actually 1.0 pixel is unknown! 

Andy
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