Need Help Getting Smooth Results with VRay SSS

[DanielBrew]

Hi,

I've been trying to use VRay SSS to simulate the effect of a coloured light behind frosted glass or Prespex. I'm quite happy with the initial result but I would prefer it to be smoother - without the blotches. I've looked in the manual but can't find any examples of settings for sss. Does anyone know what I have to change to get more gradual illumination.

The image below shows what I mean.



BTW I'm using sss because I'm getting green dots with glossy refractions.

Thanks,

Dan

[Saulman]

Dan, the lighting on that image is incredible.

I have no idea what you're trying to do with sss, I don't even know what you mean, I'm afraid to say.

Can't you achieve the same effects with maps behing the glass and upping the RGB settings? Bit lame, I know.

[DanielBrew]

Thanks for the comment Saulman!

The image is lit with the up/down pendent lights suspended from the ceiling + a bit of skylight through the window. The pendent light is my model so I could send it to you if you want.

You're right, I could use a map to simulate the lighting but I was trying to learn a bit more about Vray.

Dan

[egz]

Could you post the material settings you have now?

OT: AAARGHH, our delivery of three graphite Herman Miller Mirra chairs - just like the ones in the picture - are four days overdue now. Hopefully they will get here in the morning...

[DanielBrew]

Hi egz,

THe settings are as follows,



I'm just sorry I can't help with your chairs , as office chairs go it's a good choice though.

Dan

[DanielBrew]

I think I've solved it! The size of the blotches is directly related to the number and the size of the lightcache samples!

I need to do some more tests though.........

Dan

[natty]

Hi Daniel ..

The Blotches do look like Lightcache samples, what happens when you render without ? Nice lighting BTW..

[dennis]

isnt there an option to use light cache for glossy rays. Could that be it?

[natty]

what are your lightcache samples set to and what filter type ? nearest ?

[egz]

For SSS to work you should use a refraction glossyness value of less than 1.0. Try lowering it and see if that helps.

[Morbid Angel]

egz, i think for sss to work you need to lower fog value to be less then 1. Refraction glossines can produce similar to sss effect without actual sss.

[egz]

That's if you want the material to have absorption, coloring the rays as they scatter inside the object. The Refraction glossyness amount actually controls the amount of scattering in the SSS when you turn on translucency. With translucency off it is just like frosted glass though, only on the surface.

[DanielBrew]

Hi,

Natty wrote:

The Blotches do look like Lightcache samples, what happens when you render without ? Nice lighting BTW

what are your lightcache samples set to and what filter type ? nearest ?

Yes, the blotches are definitely lightcache samples. I've used relatively low lightcache settings (800) samples and you're right, I used the 'nearest' filter. I've just tried changing the filter to fixed and the result is much smoother, thanks.

dennis wrote:

isnt there an option to use light cache for glossy rays. Could that be it?

Tried unchecking 'use light cache for glossy rays' and that fixed the problem completely. When unchecked the quality of the sss is controlled by the refraction subdivs. However, the render times do increase.

I think for stills and animations using a saved GI solution changing the filter type would be a good enough compromise.

egz wrote:

For SSS to work you should use a refraction glossyness value of less than 1.0. Try lowering it and see if that helps.

I started off using glossy refractions for the effect but I'm having problems with scenes that use materials with glossy refractions. See what happens to my current scene:



The GI disappears and I get either green or red dots. I raised this a couple of months ago in http://www.chaosgroup.com/forum/phpB...559&highlight= but couldn't find a solution. I only ever use VRay materials so it's not Max's raytrace creeping in. If anyone from Chaos reads this could you tell me if this is a bug or is it something I'm doing?

I think I understand sss a lot better than I did 24 hours ago. I have to say, I'm impressed with the speed of VRay's sss - about 40 min on a dual Xeon 2.8 at a resolution of 1200x900 for the stills in this thread.

Thanks again for your help everyone,

Dan

[RErender]

Make sure the fog color of your SSS does not have a rg or b value of 255, it can cause probs.

[DanielBrew]

Thanks, I'll check.