[Leica] DMR: Hands on

[reid at mejac.palo-alto.ca.us (Brian Reid)]

>  So, perhaps, they are
> doing in software what the filter does in the light-path, and
> smoothing pixels together in some sort of way, perhaps based
> upon...??

Would that it were so.

Filters in the light path make the sensor see the right thing.

Filters in software analyze what the sensor did see, and work backwards from 
that to figure out what the image must have looked like. They do this by 
applying knowledge of what real-world objects look like, and what kinds of 
images they make.

What the word "aliasing" means is that without a lowpass filter, there are 
several different scenes that, if you point a camera at them, will result in 
the exact same image recorded on the sensor. A lowpass filter ensures that 
only one image can produce that result on the sensor.

Software filters work by having a notion of "preposterous". Yes, there are 
several different scenes that would all produce the same sensor result, but 
only one of them "makes sense" from the standpoint that the camera is 
pointed at actual physical objects.

Sooner or later somebody will point a digitally-filtered camera at a scene 
for which the software guesses wrong, and the resulting image will be 
bizarre. Oh well. Sometimes film does crazy things, too.