Vray2.0 - Fresnel enable causes artifacts

[Pixelperfectg]

I'm finding that enabling the built-in fresnel option on the VRay material, or using a 3ds Max falloff/fresnel map creates artifacts. See attached image.

[Dariusz Makowski (Dadal)]

I had that before

Its not bug I think, more like u bending physic try increase reflection or play with it a bit more, I fixed it this way

From other hand I dont think that tire got a fresnel refelction anyway, more like very low specular only.

[PIXELBOX_SRO]

just set the reflection cutoff to 0 in the material editor in options and it will work

[toby™]

Nice to know, thank you for this hint, PIXELBOX_SRO

[vlado]

Yep, it's because of the default cutoff; if you reduce it, it will be fine.

Best regards,
Vlado

[toby™]

So if physical correctness is taken into consideration, Cutoff option needs to be turned to 0, right?

best regards,
toby

[Pixelperfectg]

Ah, thanks for the info. That cutoff setting indeed fixed the problem. Funny that I've never run into this before version 2.0.

[PIXELBOX_SRO]

ive started runing into this "problem" after i ve switched to LWF....maybe its because the number of "blacks" has reduced in the colorpicker when switching to LWF settings...
anyway, what i do now is that i always use cutoff at 0 for any material that uses darker colors in the reflection slot.

[Jiri.Matys]

And what cutoff treshold mean anyway? I mean the number, there is no units, so its hard to know that number.

[PIXELBOX_SRO]

there is no dimmension so i suspect its a percentage value?
0.01 meaning 1%??

[instinct]

From the docs:

Cutoff - this is a threshold below which reflections/refractions will not be traced. V-Ray tries to estimate the contribution of reflections/refractions to the image, and if it is below this threshold, these effects are not computed. Do not set this to 0.0 as it may cause excessively long render times in some cases.

So i'd say it follows the same rules as other Sampler thresholds (DMC threshold and alike). If the contribution of the reflection is estimated below the threshold it will not be traced to save rendertime. I'd assume this is a value between 0 and 1, with 1 meaning the final pixel in the RGB will consist ONLY of the reflection.

Regards,
Thorsten

[Jiri.Matys]

Still dont know, how this number controls the render. I know when I have to lower it. But why and how much? I think doc isnt clear enough.
Color threshold for example is easy understandable, Its a difference in contrast of two pixels. So when VRay dont AA those pixels, I will lower these value. I know, You can say I dont know how much either, but its much more understandable, because we see those pixels and see the contrast.
Cutoff in VRayMtl is not clear. "below this threshold, these effects are not computed". But what this threshold mean?? Its not contrast of two pixels, so what is it?

[Dariusz Makowski (Dadal)]

Still dont know, how this number controls the render. I know when I have to lower it. But why and how much? I think doc isnt clear enough.
Color threshold for example is easy understandable, Its a difference in contrast of two pixels. So when VRay dont AA those pixels, I will lower these value. I know, You can say I dont know how much either, but its much more understandable, because we see those pixels and see the contrast.
Cutoff in VRayMtl is not clear. "below this threshold, these effects are not computed". But what this threshold mean?? Its not contrast of two pixels, so what is it?

Angle and distance in reflection I believe....

[instinct]

Well according to the docs VRay tries to estimate the contribution to the final image. As written above that would mean that 1 means the final pixel contains ONLY the reflection and 0 it doesnt contain ANY of the reflection. The estimated amount might be based on fresnel, the mask and other material properties (beeing in a vray blend with an additional mask and amount set for example).

That's what i'd interpret into the docs. Only vlado can tell i guess.

Regards,
Thorsten