Cleanup noise in Elements: Reflection and Shadow - Also LOOONG render times

[Morbid Angel]

I think what it comes down to is a clean image is a clean image, and in vray if you dont make the dmc sampler figure out too much what ray needs to be what, and give enough default samples for everything it makes the render go faster.

[PIXELBOX_SRO]

this turned out to be a really great thread! thank you guys!!!!
I think Bertrand will be happy too when he finds this )

its jsut really weird that in both threads...this one and "noise in general" one, we did not have much input from chaos guys
would be great to have a settings comparison tutorial just as Francesco Legrenzi has in his book

[Morbid Angel]

here is another test this one is with cuda, as you can see after 1 hour 40 minutes the image is still grainy, though my max noise limit is 0.005 I rendered this one on gtx 480.

[peterguthrie]

with the 'morbid technique' (or should it be 'morbid method'?) what does the sample rate element tell me? If I have areas that are going yellow/red, what can I do to speed those areas up? Or does the fact that they are red just mean they arent getting as many samples as they would like and so are already going fairly quickly? ie. would changing the dmc sampler to 2,32 instead of 2,16 make things slower, or faster?

In general, I am getting less noisy render for the same render time compared to universal settings, so thats something to be glad about

[Morbid Angel]

Vlado can answer this better then I, but typically red means redundant sampling, or too much sampling if you will.

The thing is, for more dmc samples you will need to trace even more rays for each entity, so raising the max value will actually create more noise and will not improve quality/render time. What you need to do is just lower the noise threshold instead. For the red/yellow areas, probably increase adaptive amount see if that helps. In my test renders with the images above I did not have any yellow or red, only around the border of the white where lighting is really bright but thats normal.

[zeronove]

Vlado can answer this better then I, but typically red means redundant sampling, or too much sampling if you will.

mmh, my understanding was slightly different about that.
AFAIK red an yellow means adp. DMC max rate is not high enough to satisfy the required noise/clr threshold then you need to "free" some more samples to clean that areas; otherwise it's true that high values will introduce more grain if mtl subds. aren't high enough accordingly. But, yes, I will be very happy if Vlado could say something more about that, maybe I'm totally wrong.

[svetlozar.draganov]

Hello there.
Thank you for your interesting questions about cleaning the noise - It seams your post into our forum is very popular

Regarding the noise :

In your scene all of your material are with Glossy Reflections with very low value approximately 0.6
Having material with such low Reflection/Hilight Glossiness is always producing a lot of noise in the render.
The parameters responsible to clean this noise are :

1.Material Reflection Glossiness Subdivisions
2.Image Sampler - Min-Max Subdivision / Color Threshold
3.DMC Sampler - Adaptive Amount / Noise Threshold
4.Lights Subdivision - if Affect Specular/Reflection are ON

In the scene you sent us we've noticed that Adaptive Amount = 1 - this value is not recommend for production render - especially for scenes with glossy reflections !

It is a bit hard to clean the noise if you don't know what cause it - so the first thing we need to do is to determine what cause the noise!
If you look only the Beauty-Pass it could be difficult to understand exactly what cause the noise - it could be Reflection noise / GI noise / Lighting noise etc. - to avoid this wondering we could break our scene into separate render elements :

-Global Illumination/Raw Global Illumination - (noise from GI) - increase GI settings
-Lighting / Raw Lighting - (noise from Lights) - increase Lights Subdivisions
-Reflection / Raw Reflection - (noise from Reflections) - increase Reflection Subdivisions
-Refraction / Raw Refraction - (noise from Refractions) - increase Refraction Subdivisions
-Specular (noise from Lights and Hilight Glossiness) - increase Lights Subdivisions
-SamplerRate (Image Sampler visual feedback between Min and Max Subdivisions) - increase Min-Max Subdivisions / decrease Color Threshold

Observing these render elements will point you to the right parameter responsible for this noise. In addition to this parameter you should know that Image Sampler and DMC Sampler always affect the noise in the scene and they should be tweaked as well.
The procedure here is to find the render element with the most prominent noise and to reduce the noise on it - when you clearing this noise watch both Render Element and Beauty-Pass. Don't try to make perfectly clean Render Element - in most cases a small amount of noise in Render Element is unnoticeable in Beauty-Pass.

Let's move to some practical situation - for example we find noise in Reflection Render Element - remember three things affect this noise:

1.Glossy Subdivisions
2.Image Sampler
3.DMC Sampler

The first one is the most important - Image Sampler and DMC Sampler are working with Glossy Subdivision - so if you don't have enough Glossy Samples they don't have what to work with. So the first tweak should be increasing the Glossy Subdivisions - I usually increase this subdivisions on steps - 16/32/48/64/80/96/112/128 etc. and doing test render on small region and paying attention to Reflection Render Element and Beauty Pass !
If this increasing remove the noise everything is OK , but if you still have noise using very high Reflection Subdivisions above 128 obviously the issue is somewhere else!

We have to tweak the Image Sampler and DMC Sampler.

A good starting point with DMC Sampler is its default values Adaptive Amount = 0.85 Noise Threshold = 0.01
I usually start to decrease Adaptive Amount on steps - 0.80/0.75/0.70/0.65/0.60
and Noise Threshold - 0.01/0.008/0.006/0.004
Remember this Parameters affect almost everything in your scene - they don't affect only reflection noise , be very careful when you adjust this values otherwise you will get excessive render times.

About the Adaptive DMC Image Sampler - a good starting point for scene with a lot of Glossy Reflection are:
Min Subdivisions - 2
Max Subdivisions - 6
Color Threshold - 0.01

I usually use 2 or 3 for Min Subdivisions.
Max Subdivisions increasing on steps 6/8/10/12/16
Color Threshold - decreasing on steps 0.01/0.008/0.006/0.004

For Color Threshold I observe the SamplerRate Render Element - This element gives the visual information about Min and Max subdivisions - Min Subdivisions are represented by blue color - Max by red color - for the best results this image should not be completely blue completely red because in this situation Adaptive DMC is not adaptive at all. To determine how much of this colors appear on the image you have Color Threshold.
If the image is mostly in blue this means that Image sampler use mostly Min Subdivision Value - if there is no noise on the image that's fine but if you still have noise you should decrease Color Threshold a bit - this will force Vray to start use more samples on some difficult areas !
If the image is mostly in red this meas that Image sampler use mostly Max Subdivision or your scene - but if you still have noise you have to increate Max Subdivisions.

Remember Image Sampler as DMC sampler affect not only the reflection in the scene but entire appearance.

Ok we have adjusted Reflection Subdivision let say to 80 but we still have noise - what I do is to start adjusting DMC and Image Sampler on small steps , and pay attention which parameter affects it most and how much render time this change costs.
On most cases DMC Sampler has more influence and usually the noise is clear mainly by this parameter, but this doesn't mean to leave Image Sampler on its default values! I usually use this parameters together.

According Global Illumination Method.

Rendering such a scene with Brute Force will take a lot of time to clear the noise, because Brute Force produce a lot of noise in GI.
The good thing is Brute Force is quite easy to control - just increase Primary Bounces and don't forget DMC Sampler - it is also affect the noise in Brute Force.

Our recommendation is to use Irradiance Map in this situation - it will produce faster results with similar quality!

We create four renders :
1.Brute Force / Light Cache - with lower settings - (BF_LC_low.jpg) - 50min
2.Brute Force / Light Cache - with high settings - (BF_LC_high_2h30min.jpg) - 2h30min
3.Irradiance Map / Light Cache - (IM_LC.jpg) - 47min
4.Irradiance Map / Light Cache - with Material Reflection Interpolation ON - (IM_LC_Reflection_Interpolation.jpg) - 12min

All images are with very small amount of noise except BF_LC_low - the image is a bit grainy!
At the end you can get clean image with both Brute Force and Irradiance Map methods but at different rendering times!
You can see that between both render with Brute Force low and high - there is no big difference in the quality of the image but the render time increase almost 3x times and there is still noise! On the other side using Irradince Map with Reflection Interpolation ON is done for 12min and the noise is literally gone.

We have created some changes in your scene as:

-modifying all the lights
-adding a new sky-portal
-adding shell to walls
-changing materials subdivisions
-using Reflection Interpolation
-changing VrayLightMtl


http://dl.dropbox.com/u/45398240/ChaosGroup/noise.zip


Let us know if this information helps you to understand better the noise clearing procedure in Vray.

Regards
Svetlozar Draganov

[Morne]

I must say

Thank you once again for ALL that helped with hints and tips in this thread. I have already thanked some of you in PM's

To people at ChaosGroup: Thank you very much. From all my years on the forum, this is the best and most detailed reply I ever received in the forum or in email from you. Keep up the good work!

[rivoli]

From all my years on the forum, this is the best and most detailed reply I ever received in the forum or in email from you. Keep up the good work!

it's a very informative post, as the rest of this thread, it could save a lot of time to a lot of people. it should be made into a sticky in the tips & tricks forum

[rikou]

woooo !! really interesting !!! it's a very informative post !
Thanks a lot !

[zeronove]

Hi Svetlozar,

IMHO your post it's probably going to win my personal "best answer of year award"

I really appreciate it

now I have only to find another 2012 max install to look at the scene settings

[CEDRIC_JACCHERI]

Thanks all of you for this really great thread very very instructive
Is there a reason for not having AA filter in this scene ? I always use it, but obviously it's an error

[vlado]

here is another test this one is with cuda, as you can see after 1 hour 40 minutes the image is still grainy, though my max noise limit is 0.005 I rendered this one on gtx 480.

Are you sure this really rendered on the GPU? Check the RT render server to see if it is indeed the GPU, or if it simply fell back to the CPU mode. The GPU engine does not currently support environment overrides (like the GI override in your case), but this override is clearly visible in your image.

Best regards,
Vlado

[Morbid Angel]

not sure, but Im pretty sure the gpu was rendering. When my card renders it goes pretty loud. I had the gpu monitor show gpu usage 99%

[Morbid Angel]

Thanks all of you for this really great thread very very instructive
Is there a reason for not having AA filter in this scene ? I always use it, but obviously it's an error

reason being that aa filter can add 10%-20% to render time. While not the same as blurring in post, in most cases especially in still frames post blurring is more then enough.