GI material Override

[Travis Serio_cg]

So i've been playing with the GI channel at the material level and I am sort of confused. Does this channel ignore primary rays and only render secondary rays?

attached is a render that i cut a little short, I can get refraction caustics to generate from the GI that I attached, however, I cant see any reflection or lighting changes to the object itself. For example, if i turn off refract caustics there is no difference at all to the render. The only way i can get a visual difference on this glass/diamond material is if i attach Sky... then all hell breaks lose.

Is this a glitch or the way it functions?

[Travis Serio_cg]

Re: GI material Override

ok well after more playing around it seems to me that GI doesnt want to create glossy reflections off of the facets of this model. Only direct light will do it. Is this correct? Should this be correct?

[Travis Serio_cg]

Re: GI material Override

man, i am glad we had this little talk because i figured it out. If there is no diffuse layer, only reflection and refraction, glossy reflection do not work at all.

thanks for letting me think out loud in public lol

[craiggorton]

Re: GI material Override

Travis: thanks for letting me think out loud in public lol

Public: No problem. Think away.

[Travis Serio_cg]

Re: GI material Override

if it makes you feel better... i am confused again. :-[

i've got so much stuff over ridding so much other stuff that i think even vray is confused .

[Travis Serio_cg]

Re: GI material Override

but here's where I am at

What I am after is a glossy reflection on the top surface of some of the facets. Like a nice White reflection on a few of the 75 degree faces. I don't seem to be able to accomplish this using the GI over ride. I think it had something to do with the lack of the diffuse layer, i'll post more once i get even more confused ;D

[Travis Serio_cg]

Re: GI material Override

:P

[Travis Serio_cg]

Re: GI material Override

as you can see the second image shows some better face reflections in the corners. However they are just the scene back ground map reflecting, they are not the GI map from the scene or the materials GI channel. I can't seem to make the GI affect the object unless its an indirect ray cast from a near by object such as a ground plane or adjacent object. Should this be correct?

Here's an example. The ground plane is fully affect by the GI and washes the scene. However, when the plane is turned off, there is no sign at all of GI variations.

[dalomar_cg]

Re: GI material Override

I've been quite busy today, so pardon my lack of timely response. Any way...why are you doing a GI override on your gems if they are causing you so many issues???...why not put the map that you want in the regular slot and all the other things that you don't want to reference the main one(groundplane or what have you) have the other GI one in their own materials...Am I missing things, or is by brain just fried??

btw. Think out load if you need to...just don't wander the halls talking to yourself

ps Refraction caustics from GI are typically very hard to get...they usually require a very bright hdr, but thats just from my experience.

[Travis Serio_cg]

Re: GI material Override

I am trying to build the diamond material to where it reusable in a wide variety of scenes. The problem that I am having is getting the faces to create bright reflections. I am starting to think it is just a limitation of GI lighting.

Here's the overall problem.

Direct lighting in the scene creates perfect reflections on the faces of the gems. They look 3d and all is well. The major problem with the direct lighting is that the direct lighting blocks the materials background map. Well I use the background map to create the dispersion like reflections/refractions in the stones.

My thought was "okay ditch the direct lighting and try to recreate it on the stone material using GI" Here's what I have found so far.

GI will not illuminate this object any brighter than it is. As you can see by the first 4 renders the stones are almost gray and washed out. In the last picture the stone is over exposed and blown out almost completely. I am looking to get GI to balance the two effects but it wont. I get the washed out version when I turn on a ground plane. This leads me to believe that the Glass material only becomes brighter through bounce rays from the ground plane. This is what is confusing me.

[Micha_cg]

Re: GI material Override

The GI should not show any effect at the stones, because GI light affect diffuse materials only and diamond is refl/refr only. For reflection/refractions you need the material based refl/refr environment options or the gloabl ones.

[Travis Serio_cg]

Re: GI material Override

You are correct Micha, it took me half the day yesterday to realize that GI only works on the Diffuse. Man it was crazy for awhile until I realized that. I also realized that GI can never cast visible rays even when using HDRI. It has to be done via reflections from background mapping.

So now between background, reflection, and refraction overrides I might be able to get what I want. lol

This has been a fun but nerve racking experiment.

[Micha_cg]

Re: GI material Override

Experiments are the base for good renderings.

Good luck.

[dalomar_cg]

Re: GI material Override

That makes almost too much sense...good catch Micha

[Andresg_cg]

Re: GI material Override

Travis do you find it hard to render some stones? personally my baugettes look like crap and my french cut stones dont refract well either. So the only stones that do a good job are the rounds asher and princess(maybe) are you using the same background image for all your stones and if so what kind of image are you using. Thanks agian man.