V-Ray renders blank background very (too) slowly

[noel_d3]

Hi,

Something makes me lose much time in production : V-Ray renders blank background very slowly

I thing that it's probably due to a background antialiasing process

For example, for one simple pass of mask :
with some objects in white self-illum on black background without lighting
it passes much (too much) time to render the black even if nothing is behind !
then I am obliged to render thise pass in scanline which render it instantaneously where Vray spends severals minutes!
the real problem it's if I use Vray motion blur for color pass I'm obliged to use Vray (with MB) for my mask pass,
it's even longer to render where there is blank...

if you could do something in a forthcoming version ..

thanks for your work on Vray,
the plug which has reconcile me with 3ds max

best regards

Leon

[sv]

i think if you tick "optimise atmospheric evaluation" (or something similar) in the settings tab, this has some sort of effect.

I'm not entirely sure what it does, but i think it should speed up rendering of blank environment spaces.......

[noel_d3]

That does not work,

A simple example to test it :

Reset for create a new scene, increase the antialiasing ( for example QMC min 4 max 8 )
render the blank background ...
and wait

[instinct]

well of course it does...if you set qmc to 4/8 that means a minimum of 4 samples...and those are sampled no matter if there is nothing then background (well, there COULD be something in any of the 4 samples so of course all 4 have to be sampled before we know it IS background only)

Or am i off the track there ?

Thorsten

[Da_elf]

your correct as far as i know

[noel_d3]

well of course it does...if you set qmc to 4/8 that means a minimum of 4 samples...

sorry I'm not here for demonstrate this probleme but just for underline it and for ask if an optimisation is possible in a forthcoming version

but if you want you can take a fixed rate or any parameters you want,
with the motion blur you can wait a long time for render the background where there is nothing ...

Even without motion to blur it's never immediate as in Scanline

[Morbid Angel]

This is the issue that is aparent not only in vray; brazil and mental ray have it too, under extremely high aa settings.
This has also been brought up before. And I believe its not possible to solve it at this time. However perhaps in the future, vray will have an option where it can detemine before render where there is no objects in space, and simply by pass it all together.

[instinct]

Well this option would be the region render option :P

sorry I'm not here for demonstrate this probleme but just for underline it and for ask if an optimisation is possible in a forthcoming version

Well i came here to underline the fact that it is impossible to get around that with those sample settings. you might have more luck if you set samples to 1/8 and tweak the adaptive settings in the rqmc sampler rollout. cause that determines when it will take min samples and when it'll take max samples. with a setting of min samples 4 you FORCE vray to use at LEAST 4 samples...how should that be faster ? You want at least 4 samples quality in every pixel. So a pre-render visibility check would not help, as it would have to be as exact (sub-pixel accurate). So it wouldnt make things faster...rather slower i assume

Thorsten

[noel_d3]

perhaps in the future, vray will have an option where it can detemine before render where there is no objects in space, and simply by pass it all together.

Yes I think that it's the best solution ! .. at first

PS : region render is not adapted for animation

[flipside]

Yeah this problem is very annoying, and it also happens with qmc aa set to 1/4

[noel_d3]

... yes and especially for integration in video where we often render small objects on black bottom with camera motionblur

on this subject thank you flipside for your HDRI maps ^^

[plastic_]

i can't believe that it's a hard problem to solve.
even if there is no way for the renderer/sampler to quickly detect black areas, a prepass could be used. like, if the lighcache/prepass of the current bucket only contains black pixels, there should be nothing to render either?

[instinct]

well that´s not really true...a prepass is at a very much lower accuracy....so there could be let´s say a quarter pixel that HAS geometry...so that pixel wouldnt be rendered and you would loose all the quality you wanted to force in with high qmc sampling settings. As mentioned above the only way i see is sampling a rather big bounding box in 3d BEFORE rendering anything and using that. Similar to region render, but adaptive to object extends with a few pixels safety region....but am not sure it would work...might be something is till overlook