Sampling tutorial for V-Ray 3.20

[pixela]

So if you had an msr of 6 and a max subdivs of 10, you'd be casting 6*100 rays per pixel.
If you had an msr of 12, and the same max subdivs, you'd be casting 1200 rays per pixel, twice the original amount.

Thank you Lele for the explanation.
There is something I don't understand clearly:
Let's say:
MSR=6 MaxSubdiv=10
So we have 6*100 per pixel.
As I understand, MSR is a like a multiplier for the max number of rays per pixel.
I thought it was some kind of a ratio, to split some rays for shading effects (such as glossiness) and some rays for other noise (scuh as DOF, GI etc)
If MSR is like a per pixel multiplier, why doesn't it have any effect on DOF, GI, bump etc?

[^Lele^]

umh, MSR is short for MINIMUM shading rate.
The way it's being used, makes it behave like "shading rate", without "minimum".
That's because the global subdivs multiplier is set to 0, or in the new builds, the local sampling settings for shaders and lights is assumed to be 1.
MSR will drive exclusively the so called "secondary" rays, such as shaders, lighting, brute-force GI.
DoF, Moblur, and Edges' AA are entirely governed by the AA samples.

It may hep visualise the rendering as two separate stages:
In the first, a (camera, or AA, or primary as preferred) ray gets shot in the dark, in the hope it finds SOMETHING at all.
In the second, if the ray above found something, it will "call home" to the secondary rays, driven by MSR, so that they can do the specialised work.
Then we move to a new camera ray, be it in the same pixel, or in another, and the loop starts all over again.

So, MSR will make sure that if stuff is found by one AA rays, those many specialised rays are called to help shading the pixel.

Did i reply on topic? ^^

[peterguthrie]

thanks Lele, really good explanation

[pixela]

umh, MSR is short for MINIMUM shading rate.
The way it's being used, makes it behave like "shading rate", without "minimum".
That's because the global subdivs multiplier is set to 0, or in the new builds, the local sampling settings for shaders and lights is assumed to be 1.
MSR will drive exclusively the so called "secondary" rays, such as shaders, lighting, brute-force GI.
DoF, Moblur, and Edges' AA are entirely governed by the AA samples.

It may hep visualise the rendering as two separate stages:
In the first, a (camera, or AA, or primary as preferred) ray gets shot in the dark, in the hope it finds SOMETHING at all.
In the second, if the ray above found something, it will "call home" to the secondary rays, driven by MSR, so that they can do the specialised work.
Then we move to a new camera ray, be it in the same pixel, or in another, and the loop starts all over again.

So, MSR will make sure that if stuff is found by one AA rays, those many specialised rays are called to help shading the pixel.

Did i reply on topic? ^^

.
Thanks Lele, great explanation

[Richard7666]

Vlado, is there going to be an "override global sampling settings" option of some sort in the materials/lights themselves?

Would be easier than overriding it via each object's V-ray properties

[vlado]

Vlado, is there going to be an "override global sampling settings" option of some sort in the materials/lights themselves?

Nope. That's why you have the subdivs there, what would be the point of adding another control for the same thing?

Best regards,
Vlado

[Richard7666]

^quite true; I originally misunderstood the purpose of the 'per object' trick

[leo.surrealismo]

hi vlado, did you have time to check my file?

vlado, I've send you a 3dsmax scene to your email.

[Oleg_Budeanu]

Wonder one thing , if my render using this settings on 0.001 Color threshold gives quite noisy result , Min shade rate is 8 , and i do not have any kind of grass fur and etc , it's a kitchen - should i decrease MinShade so AA will do the job removing that noise ? It is mostly lights noise.

[vlado]

Wonder one thing , if my render using this settings on 0.001 Color threshold gives quite noisy result , Min shade rate is 8 , and i do not have any kind of grass fur and etc , it's a kitchen - should i decrease MinShade so AA will do the job removing that noise ? It is mostly lights noise.

How many lights do you have? Turning off the probabilistic lights option might help.

Best regards,
Vlado

[Oleg_Budeanu]

I have 3 photometric lights (not VRayIES) with VRayShadows on and 1 usual vraylight shining on a reflection plane from behind. Looks like i am getting noise from photometric lights. Was thinking - will VRayIES give less noise in this case ? Also i have reflective caustics turned on.

Up : Just checked - the only noisy channels out there are reflection refraction and GI. First i thought that's about GI reflective caustics , though noise is still there after i turned it off.

Up 2 : Found out that it's only one VRayLight giving this GI noise - shining on a bouncing plane , on which there is just slightly desaturated texture.
Increasing Min Shade rate to 30 removed noise a bit , though Sample Rate channel is still red on that part.

Resolved. There was just no enough information for sampling, added some lights and it went pretty good. Though it's quite interesting that some GI shadow were quite sharp even with very low sampling for irradiance map (this was used for first version of render).

[WilleViz]

Outstanding and clear tutorial, Vlado!

It makes things very easy to setup and get going which is important for me as I'm coming from MODOs renderer.

I would love your thoughts on some good quality settings for GI as well. So far I'm going with either IM/LC or BF/LC, but BF/LC can be tricky to get noise free fairly quickly (as is the nature of BF), but I would like any input to tweaking that.

I guess another option is that I should start playing more with RT GPU with BF/LC. Hmmm.....

[3LP]

Ah ha that's always a good option too

[Oleg_Budeanu]

Here i have a workflow where our basic setup is consisting of bouncing planes behind windows with vraylights shining on them from top and couple of bouncing planes from different parts of the scene. On a plane it is a jpeg file with outside image. No portals in windows and ets. Environment is black / gray.
So scenes are lit completely with GI , only some parts may be lighten up by IES lights shining from different angles giving small amount of direct lighting.
I tried this setup and in some cases it works pretty nice (comparing to 1-100 universal settings) , but i came to a scene where with 0.005 ClrThresh i am getting completely red maximum AA samplerate even on walls, with shading rate on 8. Walls are without some heavy texture/bump , nothing complicated. So i came to conclusion that AA tries to get into GI Bruteforce cleaning, so i tried to go with higher MSR / higher subdivs on walls object. It came out that i need to rise MSR to about 80 or object subdivs up to 50 to get AA calm down and shading to kick in , cleaning noise more effectively and not giving 21 hr rendering time with about 8 spawners in.
So actual question is - what is the efficient workflow to deal with such kind of situation , when almost whole scene depends on GI , is it normal to go that high on MSR ?

[vlado]

Yes, you might have to use higher MSR in that case.

Best regards,
Vlado