Le 17-03-23 à 01:25, dick balaska a écrit :
> Am 2017-03-09 09:21, also sprach clipka:
>>
>> I suspect what you're seeing isn't actually the wood grain, but a moiree
>> pattern created by that wood grain and the pixel grid.
>
> https://xkcd.com/1814/
>
> It sure looks and acts like a moire.
>
> But, but, but, why is it only an issue when I change the angle of the
> camera on the object, and not the distance.  And why do I only see this
> with woods at any scale and not stones or other fractals at any scale.
>
> It seems odd.
>
>> What you would need to do is to enforce some stochastic oversampling,
>> for example by adding a bit of focal blur. Alternatively, you might want
>> to try UberPOV's anti-aliasing mode 3.
>
> Focal blur is out of the question. UberPOV, hmmm...
>
You also get a moiré effect with onion, gradient and checker. If you use 
the cells pattern the moiré is almost inexistant.
wood, checker and onion are periodic pattern, cells is not.
Most stone are also aperiodic. fractals are also aperiodics.
Periodic or repeating patterns, when scalled small enough cause moiré, 
while irregular patterns don't.
By small enough, I mean that the details are pixel sized or smaller.

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