Glass rendering

[ITdreamer]

Hi!

I am trying to render a glass cup, and it is close to what I need, but I can't get rid of a black tint in top f the cup. I use PBR.

What I need to tweak to get rid of it?

Edited July 20, 2009 by ITdreamer

[deecue]

i could be wrong but is it safe to assume that you don't have your glass in enclosed object (i.e. a box instead of sitting on a ground plane)? If so, it could be reflecting the whole lot of nothing in the 'black' empty sky above.. could be the number of bounces you've got going on as well.. did you turn down your reflect limit in pbr at all?

[ITdreamer]

i could be wrong but is it safe to assume that you don't have your glass in enclosed object (i.e. a box instead of sitting on a ground plane)? If so, it could be reflecting the whole lot of nothing in the 'black' empty sky above.. could be the number of bounces you've got going on as well.. did you turn down your reflect limit in pbr at all?

I use hdr to light the scene, so it is not the reflection of the sky. Reflect limit in mantra ROP is set to 10, I tried to set to 40, but it didn't help.

[ITdreamer]

Looks like it depends on Outside IOR and Inside IOR in glass shader.

1 picture - Outside IOR 1 - Inside IOR 1.52

2 picture - Outside IOR 1.92 - Inside IOR 1.52

3 picture - Outside IOR 1.52 - Inside IOR 1.52

4 picture - Outside IOR 1.42 - Inside IOR 1.52

But I can't understand what I need to do to get rid of this black tint. If the differense between these values is bit then we have a more glossy look, and more tint. It the difference is small then we have poor glossy look, and no tint. How can I get good glossy look and no tint?

Edited July 20, 2009 by ITdreamer

[anamous]

I did this a while ago. Funny thing is: I put a real glass on a lightbox and it showed the same symptoms - it's called total internal reflection. So it's to be expected, normally (depending on the glass, the dark color may be tinted towards green or brown). That's the good or bad news I hacked the glass shader to do the following: if ray level is above 1, return a tinted trace, possibly multiplied by a value larger than one (overbright). That gave me something like this:

YMMV

cheers,

Abdelkareem

[anim]

I use hdr to light the scene, so it is not the reflection of the sky. Reflect limit in mantra ROP is set to 10, I tried to set to 40, but it didn't help.

do you have the same HDRI map specified in glass material's Reflections/EnvironmentMap/EnvironmentMap parameter?

you should do either that or create enclosed geometry around your scene with that map as texture and Constant material or Environment Box Material

if not then there is nothing to reflect/refract in glass if the ray is sampling empty space as deecue said

and IOR has the influence over this because the rays are bent with different angle and therefore returning different color

also what anamous said is very interesting

anamous, your render looks really fantastic, first i thought it is the foto of glass in the lightbox you mentioned

Edited July 21, 2009 by anim

[ITdreamer]

do you have the same HDRI map specified in glass material's Reflections/EnvironmentMap/EnvironmentMap parameter?

Result is the same! :-(

anamous, can you share your tweaked glass shader? I'll try to learn how to tweak glass and liquid shaders, to get such great result.

[ITdreamer]

Here is a small movie with few frames of render.

If you try to jump from frame to frame you will see flickering in some parts of the glass.

Maybe some one knows how to get rid if it?

Cup_of_Tea.mov

[ITdreamer]

Looks like nobody knows how to get rid of that flickering :-(

[DaJuice]

Hi ITdreamer,

This is something you need to fix by increasing the Ray Shading Quality of subdivison/NURBS surfaces when rendering with raytracing/PBR. Or in my opinion, the better option in this case, is to turn off subd-rendering on the cup and instead subdivide the model a couple of times.

[ITdreamer]

Hi ITdreamer,

This is something you need to fix by increasing the Ray Shading Quality of subdivison/NURBS surfaces when rendering with raytracing/PBR. Or in my opinion, the better option in this case, is to turn off subd-rendering on the cup and instead subdivide the model a couple of times.

Оh! Thanks a lot. It is exactly what I was looking for.