Re: Dot Simulation
Re: Dot Simulation
- Subject: Re: Dot Simulation
- From: Graeme Gill <email@hidden>
- Date: Fri, 16 Jan 2009 12:36:35 +1100
Marco Ugolini wrote:
Moirè becomes less and less of a problem as the sensor's resolution increases.
With 50MP backs, for example, it barely registers, unless the pattern is extremely fine.
This may be true of moirè between the camera sensor and the objects being photographed
(and even this is the camera maker trading poorer anti-aliasing filtering for increased
sharpness), but you can still get moirè between what you've captured and (conventional)
screening.
It's all down to fundamental sampling theory - if you want to avoid aliasing (moirè),
then you need to sample at 2 or more times the highest frequencies in the original.
If you're sampling frequency is fixed, then you need to filter your original with
a low pass filter (making it fuzzier) to eliminate those frequencies.
Of course you can try and be clever on a case by case basis if the source
and sampling have dominant frequencies, to arrange them so that the beats (aliasing
products/moirè) are not objectionable (ie. by changing screening angles, camera
angles, distances, etc.) I would guess that such cleverness might even be
something that could be automated (by suitable analysis of the dominant spatial
frequencies involved).
Graeme Gill.
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