Am 27.08.2014 08:57, schrieb scott:
>>>> I found under some conditions you get a visible pattern to the noise
>>>> when doing a low quality "preview" render with no_cache. It's almost as
>>>> if the random number generator is seeded off the pixel coordinate or
>>>> something? Is this possible or am I seeing patterns where none exist?
>>>>
>>>
>>> A simple way to check that: Launch a 2 or 3 frames animation with no
>>> changes between the frames.
>>> If there is a repeatable pattern, the images will show the same pattern.
>>> If the pattern is just random noise, it will change from frame to frame.
>>
>> OK it's the same every frame, I'll post an image in p.b.i.
>
> Actually I just realised this has an implication, that you can't render
> N times on one machine (or I assume on N machines) and then average the
> result. Should there be a way to set the RNG seed that is used for
> choosing the direction to shoot rays?

By default UberPOV will seed each thread's stochastic RNG with the 
current time plus thread number, but I guess I should change this so 
that a render started 1 second later doesn't give you the same seeds for 
threads 1..N as the previous one for threads 0..(N-1), and I should also 
look into why this doesn't seem to work for animations.

That aside, you can always specify a custom seed (or, more precisely, 
seed base, as UberPOV will still add the thread number to it) using the 
"+SSn" or "Stochastic_Seed=n" option.

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