how to eliminate blotchy shadows?

[dynaman]

one of the persistent problems that i can't seem to figure out with vray is how to eliminate blotchiness in ambient shadows. i just saw some beautiful renders on here this morning, so others have figured it out. could anyone give me some tips on settings that will help to get rid of this problem.

in these images below, i'm noticing a lot of blotchiness where the metal glazing frame meets the ceiling. for some reason, i'm also getting some blotches on the wood wall, even though it is receiving direct light.

here are some of the specs from my scene:
- i rendered the irradiance map at high quality; global subdivs set to 4; my light cache was set to 800 in 4 passes.
- most of the GI is coming from environment light and a direct light (sunlight); the cove lighting is generated from a light material

is it possible that geometry could be causing the problem? all the modeling was done in max so it is clean.
as much as i am loving vray, i have yet to produce a final render that i am totally satisfied with. if i could figure out the blotchy areas that would take me much further.
thanks in advance for any suggestions!

OVERALL SCENE



BLOTCHY AREAS AROUND FRAME



BLOTCHY PATCHES ON WOOD

[aphex79]

try to post a image of your settings.. what version do you use?

[dynaman]

here are the settings i used for a 4800x3600 render. hope you guys can find something i'm doing wrong!

[gunny263]

Looks to me like your irradiance map min/max settings are way too low. You are undersampling the points too much which gives you the effect on the wood wall. Try turning your global multiplier down and your IR map settings up to balance out the time/quality.
Try -4/-1 for a starting point and see what you get on the wood wall

[dynaman]

gunny263, thanks for the feedback. but keep in mind these were the settings for a 4800x3600 image. my logic was that if i started at -3 / 0 for a 640x480, then for every time i double the image size i could lower the min / max, therefore, 1280x860 = -4 / -1, 2560x1720 = -5 / -2, and 5120x3440 = -6 / -3.
i'm pretty new to this, so i mention this with all due respect. i could give it a try at -4 / -1, but i can only imagine what that is going to do to my render time...

[RePlay]

Change your interpolation type to delone triangulation.

[alexthg]

could it be that your Hsph too low? maybe set it to 50... or higher, and see the result

and I don't think the blotchyness has anything to do with the global subdiv multiplier (?), so it could come down to 1, CMIIW pls

r u using stored with irradiance map vraylights? or using vraylightmtl for lighting?

[RePlay]

Also check your shadow bias.. see if it is over 0. if so reduce it so its 0.

[dynaman]

could it be that your Hsph too low? maybe set it to 50... or higher, and see the result

and I don't think the blotchyness has anything to do with the global subdiv multiplier (?), so it could come down to 1, CMIIW pls

r u using stored with irradiance map vraylights? or using vraylightmtl for lighting?

i thought the global subdivs effectively multiplied the Hsph, so in essence in this scene the Hsph would be set to 120. there were no vray lights in this scene (except for the glow under the desk). all other lighting was from skylight, direct standard light, or light materials.

Also check your shadow bias.. see if it is over 0. if so reduce it so its 0.

Change your interpolation type to delone triangulation.

where is the shadow bias control? is this in the light setup?

i'll try both these suggestions and see how it looks. probably won't get a chance for another day or so as i'm now on to something else...but i will for sure post results when i've had a chance to experiment.

thanks for the continued feedback...

[mcnamex]

dynaman , try increasing the hsph to 50 and samples to 50 as well

[gunny263]

Try this:

Lower the global multiplier back down as it is a likely culprit of inflated render times and keep your low ir map settings but animate your camera from frame 0 as your final shot and at frame 1, dolly your camera in to cover the wood wall. Turn off 'render final image' when doing this, use incremental add to current map, save it out and reuse it for the final render. This should force vray to add more samples to the wood wall while keeping your render times within reason. You need more samples in that area for some reason and this is a faster way than simply recalculating the entire scene at higher settings.
I really wouldn't worry at all about the artifacts you see where the framing meets the ceiling. Take a look at some real buildings and you see all kinds of 'flaws' in the perfect world of CG. The wood wall, though, yeah - need to nail that one down.

[dynaman]

gunny263 - very interesting suggestion. I never would have thought of that, but it makes sense. i will have to add that to the list of things to try.

mcnamex, i will also try increasing the interp samples to 50, but my suspicion is that in other areas of the image the reveal lines will start to show light leaks.

well, i have a chance to test out a bunch of these ideas in a new project that i'm starting today. i'm doing another view of the lobby, looking 90 degrees to the right so it'll be a good opportunity to put them to the test. i will post results soon.

thanks!