URGENT : Splotches on 7500x7500 render!!!

[R_Cyph]

Hey!
I've got this massive 7500x7500 poster due tomorrow. I'm getting thise odd splotches and I'm not sure whats causing them. I intially used a skylight color and the 7500x7500 render turned out fine. I've since switched to an HDRI map and i'm getting splotches in the lighting. I have feeling its the Irradiance map settings.

1) Does HDRI maps need Higher settings than skylight for the same quality ?

2) what IR min max settings should I use for such a high res ?

3) I intially used such low AA color thresh/rQMC settings due to the high res and using a sky light seemed to be fine at those settings during testing. With an HDRI map now lighting the scene, do I need to increase these as well?


Settings :

IR : -6/-4 medium preset
LC : 1000 .01
AA : 2/4 area filter color thres .005
QMC : adap : .85 / .005 / 8 samples/ 1 global subdiv

I've shrunk down to 10% for you guys to look at, also ignore the gamma issue for the render. Thanks in advance for any advice you can give me

[percydaman]

raise your hsph subdivs. Yes HDRI images require ALOT more samples. blur your hdri map. Try using the search function also, there's NUMEROUS threads on this kind of problem

[Shimakaze]

Hmm do you use a large hdr image? if so try to change it's size to much smaller. like just 200 pixels wide and apply a strong blur filter to it. Use that for the light and keep the original hdr image for the reflections.

[R_Cyph]

raise your hsph subdivs. Yes HDRI images require ALOT more samples. blur your hdri map. Try using the search function also, there's NUMEROUS threads on this kind of problem

ill try raising my hsph subdiv, but i've never had to with HDRI maps before.

I tried searching under HDRI + Irradiance map + settings, but nothing really answered the questions I had :P

are -6, -4 min max settings for 7500x7500? I read somewhere that for everytime you double your res from 640x480, you should descrease your IR min max settings by one. is this correct?


ex. -4/-2 @ 640x480
-5/-3 @ 1200x ....
-6/-4 @ 2400x ....
-7/-5 @ 4800x ....

I used -6/-4 because I was sure if this was 100% correct and it seemed to work for large res on other projects.

[R_Cyph]

on a side note. I'm loving the VRimg format. I can render a 15000x15000 poster no problem. only uses like 2.x gigs of ram

[studioDIM]

Put the HDRI into a VRay dome light, set the light to "store with IRMap", raise samples to 32 or so, leave the rest to the defaults.
Set your IRMap to -6/-2, default the rest to the High preset.

This will use the importance sampling from the dome light to concentrate sampling on the brighter areas, those responsible of the most color variation.
Storing it with IRMap will avoid you a direct GI pass, that could take long and introduce unwanted noise, if you want to keep rendertimes slow.

The irmap calculation will look different, take slightly longer, but if the splotches on the back wall were coming from the hdr they will most likely be sorted.

Lele

Edit: to trade speed versus precision, raise the IRMap max rate to 0 (so -6/0), as that will capture all the nuances and soft shadows from the HDR map.
It's WELL worth it, if you can spare it the time.

[studioDIM]

Quick diffuse-only sample to show the difference.
IRMap Preset "high", modified as -6/0, rest to default.
Secondary, Qmc, all to default.

Dome light with "kitchen.hdr" from Paul Debevec, 32 subdivs, store with IRMap, resolution for the map sampling 256 (instead of 512).

Fixed AA @1for both, one has the hdr as background, and the dome light is off, the other has no BG map, and the dome is on.
In this particular case it's even faster to use the dome, not only cleaner, by a margin.




Lele

[R_Cyph]

Well I can definately see a huge difference there. and Ill use those settings since always seem to know what you're talking about. But, i'm still confused about the min/max settings for the Irr. map. Also you mentioned changing the vraydome light subdiv to 32. doesn't the IRR map settings override this setting?

why -6/ 0? isn't the high preset -3/0 ?

I understand that 0 calculates the Irr map at same res as the render and -3 is supposed to speed things along and calculate all the flat areas faster. is the -6 setting because its such a huge render? ( 7500x7500 ). Please elaborate

[dominiquelaksmana]

i guess that -6 is for those area not needing high sampling. correct lele?
so your background is calculated with -6, and your detail with 0.

[studioDIM]

http://www.chaosgroup.com/forum/phpB...asc&highlight=
A sample of the behaviour of the IRMap when using a high min/max scissor.

http://www.chaosgroup.com/forum/phpB...=153359#153359
A test on how sampling works when using a domelight, embedded in the IRmap and in direct mode, versus pure IRMap and BG, without importance sampling, in an extreme case.

Basically the IRMap sampler is really clever in choosing where to sample, but i feel it works better if i leave it some form of spatial (screen-based, of course) breathing room.
If there are wide, flat areas, this will help a lot smoothing out the splotches, and speed up the IRMap calculation, thanks to the same sample rejection mechanism.
It may be entirely ineffectual if the scene is of "Greeble" look, as the well spaced -6 samples will be overridden by the finer ones in subsequent passes.

As for the dome, it works really nicely with the IRMap.
The sampling in the shadow subdivs is needed to help define the shadow nuances. Try lowering it to 1 and check the difference.
Your IRMap calc will be faster, but the results will be a lot poorer and shadows blurred and jagged.
It's a lot easier on the rendertime to raise subdivs when using the IRMap, than to do that in direct computation mode.
Think of it as the same-ish process as reflection/refraction glossies interpolation.

Lele

[dominiquelaksmana]

i am gonna have a revolution here after this thread. thanks alot lele.

[R_Cyph]

http://www.chaosgroup.com/forum/phpBB2/viewtopic.php?t=18442&start=0&postdays=0&postorder =asc&highlight=
A sample of the behaviour of the IRMap when using a high min/max scissor.

http://www.chaosgroup.com/forum/phpB...=153359#153359
A test on how sampling works when using a domelight, embedded in the IRmap and in direct mode, versus pure IRMap and BG, without importance sampling, in an extreme case.

Basically the IRMap sampler is really clever in choosing where to sample, but i feel it works better if i leave it some form of spatial (screen-based, of course) breathing room.
If there are wide, flat areas, this will help a lot smoothing out the splotches, and speed up the IRMap calculation, thanks to the same sample rejection mechanism.
It may be entirely ineffectual if the scene is of "Greeble" look, as the well spaced -6 samples will be overridden by the finer ones in subsequent passes.

As for the dome, it works really nicely with the IRMap.
The sampling in the shadow subdivs is needed to help define the shadow nuances. Try lowering it to 1 and check the difference.
Your IRMap calc will be faster, but the results will be a lot poorer and shadows blurred and jagged.
It's a lot easier on the rendertime to raise subdivs when using the IRMap, than to do that in direct computation mode.
Think of it as the same-ish process as reflection/refraction glossies interpolation.


Lele

Wow thanks for the info. The render turned out great and rendered faster than using standard methods!!!... how did you learn so much about VRAY? none of this is in the online manuals :P


Last question I promise :

If I store with IRR map, I lose the ability to render out to a direct lighting pass since the light is no stored as GI. Correct?

[studioDIM]

Wow thanks for the info. The render turned out great and rendered faster than using standard methods!!!... how did you learn so much about VRAY? none of this is in the online manuals :P

Heaps of curiosity, and WAY too much time on my hands...

Last question I promise :

If I store with IRR map, I lose the ability to render out to a direct lighting pass since the light is no stored as GI. Correct?

I reckon, yes.
But i'm not very versed in the vray passes.
Better ask someone like Dimo, Instinct, Joconnell or whoever actually uses them in their daily tread of the mill...

Lele

[R_Cyph]

Lele You need to write some more tutorials. Get all that knowledge out to us newbs. Loved your Sun&sky Tutorial btw. VERY imformative.