Digital BW, The Print

>> OK, the whole point of doing a monochrome sensor is to REMOVE the
>> Anti-Aliasing filter because there is NO color aliasing. There is no  Bayer
>> Filter Array
>> on the sensor to start with, so why would you want to fuzzy  up the image??


> Can you still have monochrome moire?  I believe an AA filter still has value
> on a monochrome CCD for that purpose.


Yeah, that's exactly why I'd want one. Aliasing arises when a signal 
with periodic structure is sampled at a frequency less than the Nyquist 
frequency. There is nothing magical about multichrome or monochrome 
sensors that makes them immune to this phenomenon.

What this means in practical terms is that if the sensor is not Nyquist 
sampling the resolution of the camera lens, aliasing may occur. I have 
taken a number of obviously aliased images with monochromatic science 
cameras, so they are definitely not immune. (The cameras I reference 
don't have antialiasing filters, because they expect the user to be 
smart enough to adopt a suitable sampling frequency.)

It is correct (obviously) that with a monochrome or multichrome camera, 
there is no color aliasing, and this is because the spatial sampling 
frequency does not vary by wavelength. Bayer demosaicing can introduce 
its own aliasing-like effects as well, so (equally obviously) these are 
not present in monochrome or multichrome cameras. Therefore the 
antialiasing filter in a monochrome camera can pass a much higher 
frequency than the one used in a camera with a Bayer mosaic. (The 
low-pass filter used for antialiasing cuts off [not very sharply in 
optical cases] frequencies greater than 1/2 the sampling frequency.) But 
it cannot be eliminated altogether, unless you plan on using an 
extremely high megapixel count (perhaps 60 or more megapixels in 35mm 
format), or rather poor lenses.

--
Jeff Medkeff
Eagle River, Alaska