Overexposing vray render to reduce noise

[stevesideas]

Hi guys,

I have read in various threads and after google searching that a lot of people overexpose an image rendered from vray and then reduce it back down in post to reduce noise levels in the render.

Am I correct in thinking that I would have to use the vray camera for this to work. Basically using the vray camera controls to overexpose the image and burn in the extra light information ?

Other than that I can only think of putting more lights into the scene..which isnt exactly overexposing the image....

Also, im guessing I would have to save to 32bit exr image or hdr...?

Thanks

[vlado]

You could also simply reduce the DMC sampler noise threshold.

Best regards,
Vlado

[rivoli]

well, a vray cam would be pretty straight forward, but it's not the only way to do it. you can also control the overall exposure of a rendering via the vray fb. adding lights wouldn't really change the exposure, it'd change the lighting completely.
and yes, you'd have to save to a full float format. otherwise you'd loose any information in the overexposed areas making the whole thing pointless.
but I'd follow vlado's advice and try to get a clean render instead.

[stevesideas]

Cheers for the tips. I have the DMC sampler set to 0.001 already and the reflections are coming out very noisy.

[Crayox13]

You should post a sample. Maybe your reflection subdivs are low? Are you using LWF?

[stevesideas]

Yes, im using LWF. Subd's for the materials are about 40.

Will post a pic in a sec when ive done this render. For this render Ive boosted up the light inside the cabin and reduced the exposure on the vfb to see if the reflections are less noisy..fingers crossed..

[Morbid Angel]

what you can do is use a gamma correction value, instead of your burn/multiply values under color mapping. Then the sampling will be performed at the gamma level.

[stevesideas]

what you can do is use a gamma correction value, instead of your burn/multiply values under color mapping. Then the sampling will be performed at the gamma level.

Not sure what you mean by that..I already have a 2.2 gamma in the color mapping rollout. Also have "dont affect colours" checked.

The extra light didnt seem to make much difference. Let me check my materials. I do have a reflection map on my leather material. If this is viewed from a distance, would this cause noise in the reflections ?

If you look at the attachment, you will see the reflection pass I did is very noisy.

[Morbid Angel]

what is your aa settings? and what is your current render time for this frame?

[stevesideas]

AA settings are adaptive dmc. Min/max: 3/6.

Render time for a 1700x901 image is around 40 minutes.

[Crayox13]

I recently had the similar problem. I also use LWF and had a dark material of about RGB 5,5,5. Even though I had gama set to 2.2 and that adaptation checked, it seamed to be below the noise threshold of 0.001 (the lowest one). The scene was sent to Vlado just yesterday, he's working on it.

[stevesideas]

If you get any results can you let me know...need to get this sorted.

Or if anyone else has any other ideas ??

Cheers

[Morbid Angel]

AA settings are adaptive dmc. Min/max: 3/6.

Render time for a 1700x901 image is around 40 minutes.

well...with 3/6 you are not going to get enough sampling even if you put noise threshold to 0.000000001

what you need to do is give samples more range. For example, 1/8, or 1/16.
Here is why:
if you have maximum samples at 6, that means at the most darkest pixel it will sample 6x6 = 36 s/pixel. And thats a far as it going to get.
But if you have 16x16 = 256 s/pixel, you will get the refined result. The reason to put 1 for min is to give the range, the less the range, the more of a fixed sampler behavior it will have. You probably will not need to put noise to 0.001 either, a 0.005 will be enough.
Also you can knock back your reflection subdivisions to default of 8.

[stevesideas]

Ok. Thanks a lot for that explanation...it just goes to show my lack of understanding why im using certain methods....that makes sense to me now. BUT, I did also notice that part of the problem now seems to be with the face im using a bump map for various materials. I have the same map in the specular and bump for the reflection and bump maps. I turned off the bump map and now the noise levels are acceptable (with your method applied also).

So the problem now is, when I get close to certain surfaces (as the animation will require), how do i get that extra detail without the bump surface on...im sure at a closer range, the noise of the reflection wont be a problem, but at a further distance it is...

[Morbid Angel]

thats a tough one it just could be that the noise you are seeing in the reflection is not actually noise but rather your bump detail?
You may try few approaches, for example instead of bump map using displacement or, animate the bump map turn on as the camera gets closer. Its not ideal, but it might work.