V-Ray reflections : how to attenuate them ?

[edgy_k]

Hi,

I have a problem with my reflections on glass that is driving me crazy.
I attached a pic of the render. As you can see on the right of the image, the glass façade looks almost like a mirror : absolutely nothing is seen through, wich doesn't look realistic at all.

Here are the glass material settings for this particular image :
Diffuse = black - refraction = white - reflection = mid gray and fresnel ON

But I actually tried various tests with different values (fresnel on or off, changing the reflection value even to very dark values, etc...) and the result is always the same.

I already searched the forum here, and in other places for similar situations and found a few. But none of the suggestionss worked for me.

So any help would be greatly appreciated
Thanks

[Mechadus]

Hey there

I have encountered similar problems a few times myself... Glass for some reason always seems to give me more trouble than it should. I have found there are some really good tricks to making glass look like it should tho:

1 - I always turn off cast and receive shadows in the object properties for the glass objects, and I check 'Invisible to GI' in the Vray object properties. This lets more light thru the glass, and brightens everything behind it (like it should be doing)

2 - I set my reflection amount to something like 40,40,40 in the reflection color (setting this to a darkish blue-green color adds some nice effects too)

3 - Recently, I have gotten out of using refraction for glass like windows and shower stalls, because it seems that even when the IOR is set where is should be, it still really really distorts the glass. Ive had a few clients complain about this so now here is my ghetto-tastic solution: I put a gradient (not a ramp) in the opacity slot of the vray glass material Im using, and I set all 3 swatches to the same color - usually almost white. This makes the material clear with no refraction, but you still get the wonderful raytraced reflection...

Just my 2 cents, but I hope this helps


Nick Kropat

Sr. 3D artist
www.3dwebmedia.com

[kippu]

what about fog color and its value ...something like 0.01 or less ...depends on the scale

[Mechadus]

Fog color may be the answer also... I really never use the fog in my glass materials unless I need something like a colored glass bowl or something... For regular windows I normally just try and stick with diffuse colors (mostly because of render times). Totally worth a try tho

Nick Kropat

Sr 3D Artist
www.3dwebmedia.com

[edgy_k]

Originally Posted by Mechadus

Hey there
Just my 2 cents, but I hope this helps

Many thanks !
I tried your settings : turned off cast and recieve shadows + unchecked the visible to GI. Also I put the amount of reflection to about 40,40,40. And there's indeed a change : I can now see some things through the glass, especially in the lower part, and they nicely blend with the reflections. But in the upper part it one keeps reflecting the environment 100%.
Do you activate fresnel reflections for the glass ?

Also I'll try the second method although I'm not sure I understood well : What you basically do is totally deactivate refraction (0,0,0) and then control transparency through the opacity slot. But why put a gradient there ? Can't a solid color do the job ? Also, I never use the opacity slot because I seen many complaints about vray handling of opacity being very slow. Does that method affect rendering time ?

Originally Posted by kippu

what about fog color and its value ...something like 0.01 or less ...depends on the scale

Originally Posted by Mechadus

Fog color may be the answer also... I really never use the fog in my glass materials unless I need something like a colored glass bowl or something... For regular windows I normally just try and stick with diffuse colors (mostly because of render times). Totally worth a try tho

I have never touched the fog parameters in my life Do they have to do with reflections ?? I thought these served for giving a tint to the glass. Anyway, the defaults are white and value of 1.0 Should I change these ?

[alfienoakes]

glass with fresnel refections is generally considered to be the most realistic..

But.. dont just rely on the default IOR (index of refraction) this is generally set at about 1.5 / 1.6.. and it will be locked at that. Try using the following settings for your glass, but play with the IOR setting.. take it up to about 5 - 6 and try rendering again..

Reflection - pure black
Refraction - pure white
Fresnel reflections - on
IOR - about 5 and work back.

Post the results, and the settings you are best pleased with...

Andy

[edgy_k]

Hey I never thought of using "unusual" IOR values. I'll give a try to your suggestion and post a pic here when it's finished rendering.

[kippu]

fog color gives a tint and the value of 1 if decreased lets in light inside ...

Fog color - the attenuation of light as it passes through the material. This option allows to simulate the fact that thick objects look less transparent than thin objects. Note that the effect of the fog color depends on the absolute size of the objects and is therefore scene-dependent.

Fog multiplier - the strength of the fog effect. Values above 1.0 are not recommended.

from the help files .... lets see if that helps

[edgy_k]

well, maybe I'm totally wrong but to me the fog seems useless for arch viz. What I understood from the help and especially the examples is that it is very useful for a correct representation of things like glass sculptures. But I don't feel the need for that extra accuracy in teh case of simpel flat glass planes. So I guess putting it to a minimal value in order to deactivate it should be the way to go for my kind of renderings.

[edgy_k]

Here's the first attempt I made with Mechadus suggestions (first method)
It definitely resolved the problem, as the glass no longer looks like a mirror.

The second one (with IOR 5) is still rendering. I will post the result when it's finished.

// Update //
I attached the rendering with the IOR setting of 5, fresnel ON, refract = pure white and reflect = pure black... and well the problem is completely gone... as there are no more reflections any more Putting reflections to pure black wasn't a good idea.