DMC sampler and subdivisions

[Guest]

By giving DMC sampler a lot of samples to work with ahead of actual sampling you are speeding up the process of the sampling it self.

This is what I am trying to work out. I have always assumed more samples would mean higher render times. But it turns out more samples gives more room to adapt and become quicker. Is that a fair description?

[Morbid Angel]

I think less samples takes longer because DMC sampler mutates the samples and adopts them for whats needed, i.e. if there is fewer refl samples it will compensate for that and so on, but in return it takes longer. Its easy to test, if you render with brute force at lower sampling it actually takes longer then if you just give it more samples initially and get a cleaner image.

[Guest]

Surely there is a point where too many samples will make it slower? Otherwise you could just put a really high value in and then leave it at that.

[Morbid Angel]

yes, this is where the tricky part comes in where you need to find a good adaptation value and noise threshold value. For example in exterior day light scene you may not need to lower those values, i.e. leave it 0.85/0.01, its where there is dark conditions like (tron world) for example, you'd need to play with those settings vs how many samples you give upfront. What I ended up doing for a couple of projects now is I just have a global script that goes in and sets all shaders to have a certain subdivision value, same for lights, and then I select specific surfaces which are still grainy and work those a bit more etc etc.

[Guest]

Is that script available for public use? I would like to try this on some existing scenes where the subdivisions are all over the pace.

[Morbid Angel]

--set number of glossy subdivs

refsubs = 64

fn multimat_process mat =
(
try
(
if mat.numsubs != 0 then
(
for i = 1 to mat.numsubs do
(
if mat[i] != undefined then
(
if iskindof mat[i] VRayMtl then
(
mat[i].refraction_subdivs = refsubs
)
)
multimat_process mat[i]
)
)
)
catch()
)





fn singlemat_process mat =
(
if iskindof mat VRayMtl then
(
mat.refraction_subdivs = refsubs
)
)




undo off
(
for t in scenematerials do multimat_process t
for j in scenematerials do singlemat_process j
)


--set the materials to have 0.001 cutoff thresh

refsubs = 0.001

fn multimat_process mat =
(
try
(
if mat.numsubs != 0 then
(
for i = 1 to mat.numsubs do
(
if mat[i] != undefined then
(
if iskindof mat[i] VRayMtl then
(
mat[i].option_cutoff = refsubs
)
)
multimat_process mat[i]
)
)
)
catch()
)





fn singlemat_process mat =
(
if iskindof mat VRayMtl then
(
mat.option_cutoff = refsubs
)
)




undo off
(
for t in scenematerials do multimat_process t
for j in scenematerials do singlemat_process j
)

[Morbid Angel]

I think there are a few free scripts for mass controling vray mats and vray lights out there too...this is just what I got, kind of crude.

[Guest]

Awesome thanks for sharing

[Morne]

Dmitry, with your DMC settings, what do you typically use for GI? Brute force with defaults for primary and secondary? Or IRMap and Lightcache?

[Morbid Angel]

Dmitry, with your DMC settings, what do you typically use for GI? Brute force with defaults for primary and secondary? Or IRMap and Lightcache?

brute force mostly. Don't render much interiors though. I figured that its simpler to turn on brute force and let it just render, then fight with the settings, that time you spend trying to solve it usually equals to just rendering with brute force Obviously not for complex multibounce scenes, but typically most of our stuff is either exterior or hdr based.

[Morne]

brute force mostly. .... I figured that its simpler to turn on brute force and let it just render......typically most of our stuff is either exterior or hdr based.

Do you just use the default for brute force?

[Morbid Angel]

not quite, you treat brute force like any other rays that require samples, for instance if you set your lights to be of 64 subdivs to get a clean result, you would do the same with brute force.

[Morne]

Ouch! Sounds expensive in render times. But I geuss only 1 way to find out and that is to try your settings and see how much I need to tweak to still get acceptable render times. I want to rerender an old project of a fighter jet and see if it comes anywhere close to your F18 in your reel flying off into the sunset. That is just AWESOME!

So to summarise, depending on the scene, this could possible give good results?:

Your average settings for animation based on the type of projects you do:
Set all your lights to 128 subdivs
Set all your shaders to 128 subdivs (in glossy reflection)
Set your DMC sampler to 2/16
Set your DMC sampler settings to:
Adaptive amount 0.7
Noise 0.01
Global subdivs 2.0

GI: Primary and Secondary to Brute Force - set samples same as whatever subdivs you used for materials and lights

That's it? Anything else?

[Morbid Angel]

thats about right. The global subdiv multiplier though its a tricky value, I'd only really work with it if you need to achieve a very high quality grain. On the last project we had some extreme grain requirements, so our renders were grain free and for that our samples had to go even higher, its all about what you need in terms of quality. In terms of render time though, when you have 350 16 core xeons at your disposal its not really an issue

[Morne]

In terms of render time though, when you have 350 16 core xeons at your disposal its not really an issue

mama!