noise limit - amount of passes

[johan belmans]

Hi there,

before we always render with a pass limit. Very comfortable to know the remaining rendering time.
With noise limit you do not have any idea about the remaining render time.

So would the following be true?

In order to know the total amount of passes which is necessary to have render with a noise limit of for example 5%, I can render (with region) the darkest spot of my render. and see how many passes are necessary.

Or works "noise limit calculations" differently?

[johan belmans]

it is not true.
Did some tests

[maru]

Can you share the tests? ;)

[johan belmans]

Yes,
I did not save the region images but wrote down the values. I am talking about VR images, but guess this will be the case with "normal" images as well.

-the whole image 13K: 3% noise level equals 25 passes.

-region (small part approx 1200x1200 pixels):
5% noise level equals around 250 passes
4% noise level equals around 400 passes
3,6% noise levels equals around 560 passes

[maru]

Hmm now that I think of it it seems to make sense. Let's say you have a scene with some heavy GI, and clean sky, or even plain background color visible.
Select the heavy GI part -> a lot of passes required to get noise-free image
Select the background part -> instant clear image

[johan belmans]

yes true.
I am just looking for a way I can predict when an image could be finished with rendering when using only noise limit.
But probably there is no way.

[maru]

Maybe (I am not sure about this myself...) you could use the sampling focus element and region-render an area where there is a lot of white/bright color?