Glass opacity

[Tommy L]

I am getting okay at making glass materials in Viz but am struggling with one aspect. The problem is i dont know how to make a material more transparent when in shadow and more opaque when light is shining upon it? Its needed for animation as well as still, so cant do all in photoshop. I think its something to do with a 'fresnell' map as a falloff in the opacity channel, but thats a bit of a guess as i dont know what a fresnell is! Can someone explain a quick slution or point me toward a good tutorial please?

Cherrs all,

Tom.

[IC]

When the fresnel effect is applied to a surface, it becomes more reflective as the viewing angle changes.

This idea can also be applied to transparency and is achieved by using incidence angle gradients in these channels.

[Iain Denby]

. The problem is i dont know how to make a material more transparent when in shadow and more opaque when light is shining upon it? .

 

Interesting. I don't know of any material (glass or other) that becomes more opaque when in shadow.

[nisus]

Hi Tommy,

 

I suggest you download the architectural glass script at www.Scriptspot.com and analyse how different glass types are set up.

You'll learn how to use the falloff shadow/light settings and how to make 'deep' falloff effects (combined shadow/light, fresnel,...)

 

rgds

 

nisus

[Tommy L]

The glass doesnt become more opaqe, the light bouncing off the surface creates, essentially, an image on the glass (reflection) stopping you see whats behind it, ie, more opaque.

Another way to look at it is this. If you are in a room at night with the lights on, people can see in but it is difficult for you to see out. The reverse is true in daytime. This effect in architectural renderings is important for realistic external shots. I would like to know if there is a property (other than an opacity map created by an alpha channel in a clone of the light source) that can control EITHER the value of the reflection in the raytrace channel OR the opacity channel of the glass.

Sorry that doesnt make it very clear, but hope someone has had the same thoughts and come up with an answer.

Cheers, Tom.

[Tommy L]

Cheers Nisus. Top plugin.

[rivoli]

i wouldn't add any falloff or map in the opacity slot of a glass material. i've seen someone doing that for plastic (a plastic bottle for instance), that is, given the fact that plastic seems to absorb more than glass, it might be a good idea to put an intense darkening falloff in the transparency slot.

but, as long as glass is concerned, as IC said, more or less "opacity" depends on reflection and camera angle. in fact dark areas such as shadows can increase reflections, if i understande correctely your point, but i still think that changing opacity wouldn't be correct in a strickly "physical" way. that doesn't count that much since CG is neither real nor physical correct, but anyway, i just did a couple of tests just to see how much a glass surface gets more or less reflective depending on camera angles.