Text and Glass

[Tomm]

Hi all,

I've been trying to render a simple glass logo for our lab and I've been having problems. I'm using Blender 2.59.0 with LuxBlend 0.8.0 on a Windows 7 64 bit machine.

Whenever I attempt to render some blender text objects with transparent material types through LuxRender, I'm getting some odd opaque black surfaces on the letters, as seen here:

A rendering using the 'diamond' setting from the LuxRender Materials Database

This only seems to appear on the letters made mainly from straight surfaces. I've tried a variety of lighting combinations and different camera angle and settings. At the moment I'm using 6 point light sources and a couple of background planes which emit light. I've also tried increasing the subdivision of the surfaces... which helps, but still leaves tiny opaque surfaces (such as on top of the 'T'):

A rendering using the 'Rough Glass' material settings and a higher level of surface subdivision

Even when I use the default 'Glass' material setting, I'm still getting these odd artefacts:

A rendering using the default 'Glass' material settings

Could anyone advise me as to what I'm doing wrong or if there is anyway around this at the moment?

Thanks very much,

Tom

[paco]

Couple of things to check:

1) Are your normals pointing the right way/consistent?
2) Do you have empty space around it or is it totally enclosed? Might be reflecting the black bits of background - try an environment map - although not sure why this would change with subdiv so probably not the cause of the error.

[Tomm]

Heya, thanks for the response!

I've tried rendering with everything enclosed in a box of panels, but still get the same problems.

As for the normals, I have tried rendering both directly from the text object, and when I convert the text to mesh. Checking the normals seems to show them all facing outwards, and all of the box normals around are facing inwards.

[Abel]

Could you share the scene, so that apart from the geometry we could also have a look at your render and material settings?

[jeanphi]

Hi,

What path depth do you use to render? Diamond has a very high IOR so you can easily get trapped by total internal reflection.

Jeanphi

[Tomm]

I think I was using the default 'Max. depth' setting of 48 and 'Shadow Ray Count' of 1 for all of these? I was also getting the same problems with a simple 'Glass' material too.

My scene should be attached to this reply. Thanks again.

[B.Y.O.B.]

You have to use an EdgeSplit-modifier to avoid shading problems with smoothed surfaces.
Also all these point light sources aren't physically correct if you don't use IES-files on them. I don't understand why you need that much of them, they sure slow the rendering process down.
Your whole scene is not what I would use for a studio setup

[jeanphi]

Hi,

Even with IES profiles, point lights are not physical, they just happen to be handy in some very special situations, but they should be avoided.

Jeanphi

[Tomm]

Heya,

I don't normally use point lights for my scenes, as I've got to be as physically accurate as possible, but I was just mocking something up quickly to show as a demo to someone. As for the number of them, you know how it is: I was trying lots of things to get it to work!

Anyway, thanks for the EdgeSplit suggestion, I'll leave a render going overnight to see if it fixes it!

[B.Y.O.B.]

This is a border render with the edgesplit-mod.: