Understanding DMC Sampler

[vlado]

It is not a bad idea and indeed we have thought about something similar; it's too late for the first 3.0 release, but we'll see what happens after that. It will definitely wreak havoc with older scenes though

Best regards,
Vlado

[tricky]

I've not really thought this through, but you know how the Max subdivs value effectively divides all scene subdivs on materials/lights/GI etc by whatever the value is? Couldn't there be a value in brackets after each subdiv which gives the effective subdiv based upon the DMC image sampler? It would just help reiterate the effect of min/max DMC on every other subdiv value.

[RockinAkin]

It is not a bad idea and indeed we have thought about something similar; it's too late for the first 3.0 release, but we'll see what happens after that. It will definitely wreak havoc with older scenes though

Best regards,
Vlado

You're of course right that changing V-Ray's sampler UI in this manner isn't exactly a trivial task - but I'm sure you guys can at least figure out how to migrate older scenes into the new sampler UI and have them render close enough to how it did before.

I just hope it's clear how the sampler UI has lots of room for improvement... and hopefully will be given enough attention to be addressed in a (hopefully near) future release.

Would it be ok to start a new thread about it to see how people react to the idea of changing the sampler UI? I'm sure the mockup can be further improved with a bit of feedback.

[RockinAkin]

I've not really thought this through, but you know how the Max subdivs value effectively divides all scene subdivs on materials/lights/GI etc by whatever the value is? Couldn't there be a value in brackets after each subdiv which gives the effective subdiv based upon the DMC image sampler? It would just help reiterate the effect of min/max DMC on every other subdiv value.

This is a good idea as well. Depending on what it's set to - there should be a space next to it showing the min/max samples that will be taken in context to the scene's current DMC min/max.

[trixian]

I got to say I'm liking this idea more and more.
Though I must admit I have not managed to think the ramifications through completely.
I guess I trust Chaos and some of you guys to take care of the issues
Here's hoping for some UI cleanup

[RockinAkin]

I got to say I'm liking this idea more and more.
Though I must admit I have not managed to think the ramifications through completely.
I guess I trust Chaos and some of you guys to take care of the issues
Here's hoping for some UI cleanup

Good to hear! I think it'd be cool to discuss the idea with some of the super-knowledgeable users that frequent this thread, but I don't want to clog up the incredibly useful info in here for other people - so I made a new thread to discuss ideas regarding V-Ray's sampling: HERE.
Chime in with your 2c!

[stef.thomas]

So I've been using this method on my last few projects and while things started out positive, the render times seem to be creeping up to an unacceptable level again. I am fairly comfortable with how to adjust things to achieve a nice noise free image, and how to decrease render quality globally to get faster drafts. What I'm not so sure on is what to do (if anything) to reduce the render time while keeping the quality? Any ideas welcome while I delve into my previous scenes to see what I did differently!

[RockinAkin]

I've just finished writing an in-depth tutorial on the subject at hand. It was pieced together from posts that have long since been buried in this huge thread, and expanded upon to be a bit more thorough.

I'd love to hear your guys thoughts!
The Tutorial
and
A separate thread for the tutorial

Hopefully that helps clarify the subject!

[Morbid Angel]

I've just finished writing an in-depth tutorial on the subject at hand. It was pieced together from posts that have long since been buried in this huge thread, and expanded upon to be a bit more thorough.

I'd love to hear your guys thoughts!
The Tutorial
and
A separate thread for the tutorial

Hopefully that helps clarify the subject!

I think the rays should be drawn backward for the light sources, since I think their rays are traced from light to surface to camera.

[RockinAkin]

I think the rays should be drawn backward for the light sources, since I think their rays are traced from light to surface to camera.

It's actually the exact opposite - the diagram is correct. Rays originate from the camera, find the geometry, and then sample the light.

Otherwise there would be countless amounts of rays being fired out from the lights which never end up being seen by the camera - wasting a whole lot of calculation time.

[joconnell]

It's actually the exact opposite - the diagram is correct. Rays originate from the camera, find the geometry, and then sample the light.

Otherwise there would be countless amounts of rays being fired out from the lights which never end up being seen by the camera - wasting a whole lot of calculation time.

Hence why photon mapping is crap at gi - you could have all your rays fired from the light, hit the floor and then bounce out a window into space, adding nothing to the solution.

[Morne]

Can we already upgrade this thread for Vray 3? With the min shading rate etc.
So the "NEW" method is to leave everything at deafult of 8, but only change min shading rate and dmc min/max?

Or did I totally misread that?

[trixian]

Better to start a new tread (named accordingly), as it would be extremely confusing for any newcomers stumbling into this.
My guess it will all be scrapped anyway later on if Chaos implement the redesigned and (in my opinion) far superior sampling and GUI cleanup that Akin outlined in another thread.

[bhh]

Can someone quickly explain the difference between the new Min Shading Rate and the old Global Subdivs Multiplier? Even plugging in different values into the AkinBilgic calculator suggest they do the same thing and just increase the maximum number of secondary samples available to the sampling engine . I've been using Vray for a very long time and have a solid workflow for my office that has worked for us and I'm struggling to understand how this Min Shade Rate is such a game changer. My internal test are showing nothing much has really changed other than some overall optimizations I'm sure. For stills, we tend to stick to an AA sampler of 1/8 or 1/16 and then just increase glossy reflection samples, light samples, etc. where needed as we dev. It looks to me like Min Shade Rate is no different than going through and increasing all of your secondary samples throughout your file. It certainly more convenient than doing that but I guess I don't understand why someone would do that in the first place. Sorry if this comes across as thick-headed, I just feel like I am missing something terribly obvious here!

[vlado]

Can someone quickly explain the difference between the new Min Shading Rate and the old Global Subdivs Multiplier?

The subdivs multiplier will take into account the local subdivs for the particular effect (reflection, GI etc) and only multiply that by the given multiplier. The shading rate will force the subdivs to a value that causes the given number of samples to be taken for each shading hit, regardless of the particular AA settings.

You are correct that you can achieve both of these effects simply by adjusting all subdivs everywhere to suitable values. However it is not always clear what the values should be, and I myself don't have the patience to go through every material/map/light/etc every time I change AA settings. Also, I find it much easier to control the render quality from one central place.

However the main reason for the introduction of the shading rate is the new progressive sampler - without it, it would be really tricky to control the render quality.

Best regards,
Vlado