Random error with Noise level limit and Backburner

[Lomarx]

Hi,
I render an animation with backburner in frames distribution (not Corona DR) to 5 computer with Noise level limit to 4%.
I see incorrect noise in randomly frames, it was not a computer in particular but I found this problem even in frames calculated by machines that had calculated right frames (I hope I was exhaustive).

I attached a right frame and a bad frame.

Thank you

[maru]

Are you using noise limit only, or is some other limit enabled at the same time?

[Lomarx]

Only noise limit. I think it's a backburner/Corona issue because I've already rendered animations with only main pc and it was always ok.

[Lomarx]

I have the same problem with another animation even if I calculated with only main PC and I think found the problem.
The problem is the background. It seems that Corona evaluate noise on BG too, even if it's only a flat white (I use direct visibility override), so, if the object scene doesn't cover most of the render size, Corona stop the render prematurely.
The only workaround that i found is to set the direct visibility to black (it seems Corona doesn't evaluate the black bg) with alpha, and composite the right backrground in a second time.

I try with daily 1.6 but has the same problem.

If needed, i could send you the scene

Lomarx

[maru]

Are you rendering your frames in strips or other regions? If that's the case, then it is definitely possible that noise limit reacts differently to different regions. It is expected to work like this. I would suggest switching to pass limit. It should give you much more consistent results.

[Lomarx]

Could you test my scene plz ?

If you render last animation frame (450) you can see that: if i use black environment, it evaluate only the object, if i select "direct visibility override" with White color, it evaluate entire image, infact it stop render prematurely.

Could you try ?

Now I use 1.6 daily 2017-01-11, but i try with 1.5.2 too

Thank you

Lomarx

[maru]

Noise limit is set to 5.
Adaptivity recalculation is set to every 5 passes.

Black bg:
Passes:
1,2,3,4,5 > noise level 11,2 - let's continue rendering
6,7,8,9,10 > noise level 5,2 - let's continue rendering
11,12,13,14,15 > noise level  3,8 - let's stop rendering, because it is less than 5

White bg:
Passes:
1,2,3,4,5 > noise 4,7 - let's stop rendering, because it is less than 5

This is because of difference in contrast of the two images. If you add CInfo_SamplingFocus render element, you will see that the image with black background is getting much more samples around the objects (since bright and dark areas meet there), and the white background version is getting less samples (the sampling focus element is less contrasty and more blurry).
I can understand that this may be problematic, but this is just the way Corona works. It could be probably improved, but for now I would suggest switching to pass limit.

[Lomarx]

Ok, I understand, thank you.
I've only a last question: for animations  I know that, with a noise limit set to 5% or 4%, the frames are enough clean, and this rules applies to most projects, but with pass limit, how can i know the right number of passes to set ?.
I think that, every projects will have a different number of passes, depending on light, materials ecc, to reach a good clean images.
Is there a trick to know that, or I have to test every projects and time line positions, to find the right one ?

Thank you

Lomarx

[maru]

Generally noise limit is the preferred solution to keep image quality consistent. It should work fine in most cases like interior animations. If for some reason it cannot be used (e.g. the case you showed - changing bg color), then you can use pass limit. Yes, it has to be determined by trial and error. And image can be rendered in lower resolution, or the most problematic (noisy) part can be region-rendered to tell how many passes are required. This is however also not 100% reliable due to the way adaptivity works. Last option is the time limit - this works best if you have limited time to render the whole animation. You can then determine the max allowed time per frame.