Glass and transparency

[DP]

Can anyone explain to me why vray materials glass seems to get darker when you turn up reflectance? This is a primary reason why i dont use it for transparent objects and it doesnt happen in nature...

[natty]

well i think it because its acting like a real world material.....
the more reflect you use the less you will see threw it .... because you are seeing what it is reflecting and not whats threw the material ....

like a glass ball with a with a mirror surface ...your not going to see threw it are you.


Natty

[cocolas]

well i think it because its acting like a real world material.....
the more reflect you use the less you will see threw it .... because you are seeing what it is reflecting and not whats threw the material ....

like a glass ball with a with a mirror surface ...your not going to see threw it are you.


Natty

hmmm.....that's an interesting eye opener .... thanks natty.

paul.

[DP]

agreed at 100% reflectance you cant see through it but the problem manifests when dealing with less than 100% reflectance.

i agree you see less through it but it doesnt make it darker, you see less because the reflections are stronger, not because its darker. How much reflection you see is also down to the amount of light comming behind the glass as well. If you put a thin pane of glass over a peice of black and white paper you see more reflection on the black parts, but the glass is stll the same reflection strength.
Another example of this is sunglasses, theres a new trend in sunglasses where the outer lens is covered in a graduated film of reflected material. Looking at them you see reflections across the eyes, yet they have no tinting to them at all and are in fact just reflective, which is noticable by the viewer who sees things just as normal but with less glare.

I just dont see why reflection is connected to glass tint in vraymat, its not the same property at all.

Another thing i would like to replicate is when glass reflects an object of varying light and tone. When this occurs its the darker reflections which seem more transparent, the lighter reflections obscuring the transparency.

[Artizen]

i noticed that adding reflection to a vray mat also stops gi from getting through. and as you said makes the glass look darker.
but when you use a normal max mat, adding vray to the reflection doesnt affect the gi, however the glass becomes additive, making eveything brighter behind the glass
the complete opposite of the vray mat.
there needs to be a middleground, a material that doesnt affect gi, or the colour of the object behind it.

[DP]

i agree, i have found glass to be inconsistant and needing to be tweaked depending where it is in a scene when using max materials and vray in the reflection slot

[rgbxyz]

after a considerable amount of time spent on glass- to no avail- I think I should have just gone with the fishies instead of VRay. It's never really right no matter how much one screws with it.

[cpnichols]

You may want to use a fresnel falloff, this is a more realistic effect of glass. At which point the glass only gets darker at the edges, where the reflection picks up, which makes sense in general.

On the other hand, I realize that you way want a better overall control of the individual effects.

[Chris_Jones]

The physical nature of glass and in fact all materials is an photon energy balance, light in gets either reflected, absorbed or refracted.
So if you increase any of these the others have to be reduced, the input energy doesnt grow to accomodate it, that would prove to produce very incorrect looking renders.
So far i have been able to get vray to do exactly what i want to do with glass, what are you trying to place it on, as in what type of glass are you trying to replicate?

On the note of absorbtion, is that ever going to be a parameter in vray for the materials? Or is the value just assumed to be the inverse of the reflectance and refraction energy ammounts?

[3dform]

having done a lot of architectur at the last weeks I came to following result:

The Vray Glas Material (In every way you use it) is wrong and ugly.

I used every way, like HDRI image, fresnel, reflect on back side... etc...

I had so nice results when working with FinalRender in the past, that I'm very sad about no development here. (I won't go back to FR, of course)

YES! The Vray Material gets always dark with refelections, thats because it use a subtractive way to add reflection, making glas darker through this.
Some renders like MentalRay use the opposide effect 'addaptive reflection' to get overbright reflection that look very nice, but unreal.

Only FinalRender used a special code that anylise the brightness behind the glass to influence the amount of reflection. So you see strong reflection when the room behind a window is dark else if the room is bright trough light. THIS IS REALISTIC!

After struggling (really!) with my partners here in the office, we decide to take all glas windows out of the scene, make a mask (with falloffs) and put the whole reflection thing to the postprocessing in photoshop or combustion.

UNFORTUNALY Vray don't over a reflection channel, which would make our live easier...

Well I hope (Since 1 year now) that Vray 1.1 will not only a standalone render, but will improve working with Vray a lot. Else, I see the future of Vray more and more dark (LIKE WITH VRAY GLAS), because with Max 6 we all get in touch with MentalRay.

regards.

robert

[DP]

YES! The Vray Material gets always dark with refelections, thats because it use a subtractive way to add reflection, making glas darker through this.
Some renders like MentalRay use the opposide effect 'addaptive reflection' to get overbright reflection that look very nice, but unreal.

is there a way where the reflections are not either additive or subractive?

Only FinalRender used a special code that anylise the brightness behind the glass to influence the amount of reflection. So you see strong reflection when the room behind a window is dark else if the room is bright trough light. THIS IS REALISTIC!

and this is what we want

After struggling (really!) with my partners here in the office, we decide to take all glas windows out of the scene, make a mask (with falloffs) and put the whole reflection thing to the postprocessing in photoshop or combustion.

yep, for stills this is what we do most of the time

UNFORTUNALY Vray don't over a reflection channel, which would make our live easier...

we have a material we have made which makes an alpha channel of the area left around reflections of geometry in glass. This allows us to get vray to do reflections of balconies etc and then still comp in a good reflection without going over the top of the existing reflection. Unfortunately we cant render this as a pass so we render it out afterwards when needed.

[3dform]

yes it's all not so easy.

I would like to see Vray with some improvements.

1. Material ID support for Vray wrapper and Vray material
2. An Reflection Channel.
3. Better way to control glas

Anyhow you can render reflection with Vray that come from the Max standart raytracer or FinalRender Stage 0. But, these raytracer can't reflect GI.

regards,

robert

[GoncaloP]

For glass I think the best way to deal with architectural images is to increase their Depth, especialy refraction one, and if you need more reflections you can increase the IOR.
Actualy the Architectural glass facades have usualy two types of glasses with different IOR...

Gonçalo

[SteveO]

This is a great discussion on glass.

I have been getting some good results with VRay glass and reflective materials. Recently a client was asking for results which worked against what the software was designed to produce. I sent the following to my client, hopefully to educate.

"The software I use attempts to simulate reality. In the real world, the sun creates an environment where there is light outside and shadow inside a building. When glass has light in front and shadow behind it darkens and reflects. The brighter the sun shines, the darker the shadow behind, which produces greater reflection (bounce) and less transparency in the glass material. This is the natural way of it and what the software is designed to produce. Also, as the sunlight is shining down on a building, the ceilings, which we are looking up at may take on some shadowing and add to the darkening effect."

"In the real world again, we see into buildings when the lighting inside increases beyond the lighting outside - effectively the light shines out rather than shining in. Normally, house lighting is never powerfull enough to overcome the sunlight. We might only see spots of light through the glass (eg the source light bulb) rather that the light cast. So, to light internal areas sufficiently to overcome sunlight requires a huge amount of light. This blaze of internal light affects the whole scene, especially with a white building which is very reactive to light and things can begin to look wierd. In addition, when the building is internally lit (more inside than out) all reflections disappear and the glass can look very flat and dull."

The best way to see what glass looks like in the real world is to step outside and have a look. We find that in daylight, buildings, paricularly houses where rooms are small with one window, glass is dark and reflective. Commercial buildings are much more open and have greater bounced light internally, and often their lights are turned on.

All the best ...

[Phantastica]

I'd like to see regular additive reflections as an option. I don't see how a reflection can be anything less than additive light.

The whole "brighter sun outside, darker interior" sounds more like an exposure thing, which should never be controlled by the glass shader.