Hi all,
I am aware that this was probably discussed in the thread “mastering vray…”, but it would take me too long to read over 1000 posts.
I’m not sure if I understand correctly how vray works with and without “divide shading subdivs”.
As far as I understand, because computers are faster now, some people would like to increase the realism of renderings, while keeping the renderings smooth, by adding more samples to the shading rays as opposed to samples in the image sampler. That would mean more accuracy in shadows, scattering, etc. no?
With Vray as it was before V3, this was very hard to achieve because vray was changing some parameters automatically (by dividing shading subdivs) as we were adding more samples to shading rays. Correct?
By un-checking this option, the calculations become linear (sort of?), which would be nice and I understand why some users want this.
However, un-checking this, makes renderings way too slow. Does this have to do with that the default subdiv values for materials, lights, etc, are too high if they aren’t divided?
It means that someone whined a lot on the forum that other render engines worked with this option disabled and were therefore so much easier to optimize. So I added the option as a test, and as expected, they found out that it was not really such a big plus anyways.
My own preferred method for adding more shading samples is through the “min. shading rate” parameter.
The default values for materials/lights/etc are indeed way too high by default, so you’ll need to readjust everything.
Yes, in some cases allocating more samples to the shading subdivs means more accurate reflections / shadows / etc.
Close - as we were adding more samples to the IMAGE SAMPLER, v-ray is reducing shading samples to compensate under the hood. This meant if you raised your Image Sampler settings, you’d have to once again raise your shading subdivs throughout the scene to get the same amount of shading samples taken as before.
Yes, basically - what you set is what you get. Increasing the image sampler’s settings no longer effects your shading subdivs when ‘divide shading samples’ is unchecked.
Right. If you’re going to go into full-control mode and disable the ‘divide shading subdivs’ checkbox, you’ll probably have to go through your scene and reduce the subdivs value of all your lights, gi, materials, etc, to a lower value than the default of 8 subdivs.
All that said - I do think Vlado is right that simply using the Min Shading Rate is the best way to quickly balance your scene’s Image and Shading samples.
Having the option to fully control v-ray’s sampling by unchecking ‘divide shading subdivs’ is a great feature - but not needed most of the time.
But now I’m confused:
I always used Global subdivs multiplier with that purpose, since it doesn’t affect AA, according to the manual.
Would you guys say that it’s a good idea to use both? Meaning, increasing (or decreasing) the global subdiv multip, AND playing with "Min shading subdivs?
And if I use “global subdiv mult”, how is it affected by the “v-ray is reducing shading samples to compensate under the hood” when “divide shading subidvs” is checked?
No; would be a lot less confusing it you stick to just one of them.
And if I use “global subdiv mult”, how is it affected by the “v-ray is reducing shading samples to compensate under the hood” when “divide shading subidvs” is checked?V-Ray first multiplies the samples, and then divides by the AA subdivs, same as before.
<shrug> Here are my tests with mr; will get to the V-Ray tests a bit later. You can see that increasing the IBL quality initially results in worse noise and faster render times, which is quite similar to what happens with V-Ray. After a certain point, increasing the IBL quality gradually improves the noise and increases the render time. When the render time gets to the same level as the first image, the noise in some parts is better (but worse in others - I think it depends on the HDR image).
It’s a bit difficult to figure out what happens with mental ray, as it doesn’t allow to enter samples for IBL directly - I’m not quite sure how the “quality” maps to the number of samples. I’m also not sure why the unified sampling has both “quality” and contrast/noise thresholds and how they relate to one another (as they both have an effect on the image).
Here are also some tests with the V-Ray scene; however I can’t replicate your results - increasing the dome light subdivs always leads to less noise and longer render times. Maybe it’s due to the particlar HDR image; not sure.
Its not only with IBL. Its the same way with Materials and normal lights.
Basically the way I see vray with samples is
1 - not enought samples >noisy light/material> AA takes over cleaning of images > Long render times
2 - Just enought samples > smooth light/material > AA dont take over cleaning of images > faster render and cleaner
3 - Too much samples > smooth light/material > AA dont take over cleaning of images > Longer render times due to oversampling.
Then again I’m probably totally wrong :- )
Best way is to look at sample rate pass. If you have red in other areas than complex contrasty textures and edge of geometry then you are wasting render time using AA to do the job of materials/lights due to lack of samples.
As RockinAkin said before: > I do think Vlado is right that simply using the Min Shading Rate is the best way to quickly balance your scene’s Image and Shading samples.
As you know, we always want more.
So I’m thinking that it would be nice that the global subdivs multiplier came after the samples division. That way we can control the balance between AA and samples with min shading rate AND, if we need more samples (less noise in shading) we can add them with the global multiplier.
Hmm, I don’t know if that’s really the case. The AA sampler will always try and clean up whatever noise there is between the 2d pixels, it’s in a way not aware of what the dmc sampler is doing and only operating on the combined results of light, material and gi sampling. Rendering goes initial ray > dmc sampling (mat / light / gi) > combine dmc results > Back to the aa sampler to judge based on colour thresh. There’s no way to kind of decouple AA sampling from judging the noise of materials for example and “compensating for noise” as you say it, the aa sampler is almost kind of working on a 2d image so the noise and colour threshold between each pixel is pretty much the only thing is has as information to work on.
What Dadal is suggesting will remove vray from making adaptive decisions (and of course lose a lot of speed benefits) but you’re right, I don’t think it’s possible to do what you’re asking and I’m not sure why you’d really like to do it either
I’d be very interested in an uncoupled AA too. (If at all possible)
I think we all went through what Recon describes. In some cases it would be good to turn V-ray’s “automaticallity” off for a while.
And I think this is key: > I would at least like if it worked predictably.
Ah okay, it might be that you’re thinking that “divide shading subdivs” does more than it really does. All divide is doing is preventing vray from dividing subdiv settings by your max aa number, so it’s kind of hiding a ui thing in an attempt to stop you having enormous ray counts, it doesn’t however change the way vray will work towards final quality in terms of the colour threshold and how your aa samples deal with the results of your DMC samples.
If you got what I think you’re asking for which is having your AA quality totally decoupled from your dmc sampling, you’d first have to figure out how the aa sampling is going to base it’s quality decisions on. Will it be the normals of an object? Will it be colour values that comes back from it’s sampling? If the two didn’t talk to each other at all and left all the control up to you I could see vray trying to make decisions on very little information and giving you some pretty bad results and nasty render times.
Righty - The coupling of subdivs that happens in vray is definitely as simple as just the ui dividing all your subdivs by the max AA - that’s all it does, there’s nothing going on at a core level. Beyond that all the sampling is just vray dealing with noise.
On image A versus image B I totally understand and really what’s happening here is just that there are many different ways to try and achieve a clean image, and it’s probably possible to get a clean image using any of those methods but some methods are better suited to certain scenes than others. The various approaches to sampling really boil down to do I want to spend time optimizing my settings for quicker renders, or do I want to use less controls and have sightly slower renders. Vlado would love to boil it down to just one method of working as it means the ui could be simplified, learning vray could be simplified and we could all move on - the problem is there’s people like me who endlessly fiddle with vray and we’ve gotten used to a different way of working from universal type setups. It’s always really tough to remove a bit of functionality from software, even if it’s a worse way of doing things as you’ll always find someone who relies on it heavily. The autodesk guys for example would love to throw out editable mesh and editable poly as it causes a tonne of problems for them, but so many people use max in such different ways that there’ll be someone that’ll cause uproar if their favourite button gets removed!
In terms of the extra check box, what it did was add in yet another method to optimize vray and while that works really well for some people, it’s adding in another control and Vlado would really love to simplify, not add to the ui. The problem it was put in to resolve, it’s definitely solved (which is only to stop max AA from dividing all your other ui controls) but it might be that you’re expecting it to do something different?
As John said - all it does is stop the AA max samples from dividing your scene’s secondary samples values (lights, gi, materials, etc).
The calculator will show you how the formula changes when you check it on and off.
