fire3d

After using Brazil R/S for some time I decided to get with CGIs architectural adopted format VRay. Honestly, I feel comfortable with the renderer at this point. What I am looking for is more information on rendering passes with VRay. I didn't really have a lot of experience in architectural visualization or composting so I purchased Tim Jones's DVD Environment Creation for Production. Working through his online tutorial http://www.seraph3d.com/CompositingTutorialA02.htm he gives examples of rendering passes with the scanline renderer.

My issues is that I can't get my passes to look correct with VRay. After spending two frustrating weeks with this I am at my wits end. So my question is is there a more definitive guide on rendering passes with VRay?

I did find a nice script by Marc Lorenz to quickly render ambient occlusion in VRay.

http://plugins.angstraum.at/vrayao/index.htm

DavidR

watching this thread

bigroo

I'd say the best (& free) definitive guide to Vray is at http://www.spot3d.com/vray/help/150R1/ and it sure helped me when I first started looking into it.

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All things in nature are dark except where exposed by the light. Leonardo da Vinci

Christopher Nichols

You will find that most people that use Vray will find no use for AO unles they want an extra bit of dirt. Which is why the AO shader in Vray is called a VrayDirt. As far as making passes and compositing back together, I did this a while back

http://www.chaosgroup.com/forum/phpB...ic.php?t=13818

Vray can split out all the relavent layer info and can be reconstructed in comp.

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Christopher P Nichols

martin walker

[quote=Christopher Nichols]You will find that most people that use Vray will find no use for AO unles they want an extra bit of dirt.QUOTE]


Christopher, Im intrigued by that comment. I use AO quite considerably, especially coupled with a direct light I get excellent rendering times for a decent result.

Ive found the v-ray lights extremely slow and grainy, especially in interiors

Id be interested to hear your reasoning behind not using AO and opting for V-Ray lights.

btw....your DVDs where a great help when i first started using V-Ray !

Christopher Nichols

[quote=martin walker]Just keep in mind that the whole AO pipeline was developed for people that don't have the luxury of full GI, such as renderman users. They needed a way of creating the "look" of ambient light without having to calculate it. So elaborate AO pipelines were developed, starting with Pearl Harbor. With Vray GI is practically free, as light, especially diffuse light, bounces around very fast and nicely. I always use these two images as examples of that:




The math is the same in either case, just multiply it by the diffuse color... it is just that you get the proper light bouncing around. Like I said, sometimes people use the AO pass like a dirt pass to darken corner. Never use an AO pass on an interior unless it is for dirt. The only way to get ambient light in an interior is to have it bounce around.

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Christopher P Nichols

martin walker

Thanks Christopher

I think im getting my terminlogy confused, isnt AO the process of using the ambient /environment colour as a "light" which is bounced around by the GI ?

or am I mis-understanding the process ?

AJLynn

The AO Chris is talking about is a pass for faking GI. Basically, when rendering, from each sample point draw a hemisphere over it and randomly shoot some HSphere rays. If they hit something, they return dark. If they don't hit something, e.g. they escape to the environment or hit the max distance, they return bright. Average the darks and brights to get the shading.

So it's not based on actually bouncing any light, it just darkens a surface according to how much of its environment is "occluded" by other objects within a certain distance. It's really good at darkening the inside of your corners, if you have a radiosity render and you need to add a bit of "something", some kinds of dirt, some NPR techniques, but for our purposes when doing Vray renders it's easier, faster and looks better to do real GI instead.

Christopher Nichols

Exactly as AJ tells you, but most people that use AO want you to think that it is in fact the light from the environment. Compared to true GI, it is far from it. I laugh when I read articles that claim they do GI via Ambient Occlusion. That is like saying I drive my car via ridding my bicycle. In order to be consider global illumination, the scene need to be illuminated by everything in the environment, including the scene itself. AO does not collect color, and does not bounce. Again, the GI method that is done is Vray is something that many places wish they had. That is why many mid to high end VFX places are switching to Max and Vray (or other GI rendering) just to have access to fast GI. The only thing that is stopping really big VFX shops is that their pipelines are so tied to their current system. It will take years for them to switch.... plus renderman has so much legacy, it will take years and years for it to adapt as well. Keep in mind that Renderman is a rendering engine that just got multi-threading this year.

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Christopher P Nichols

Christopher Nichols

One more thing.. Dirt is based on the AO thing. In the new Vray, there is a dirt shader. It is pretty cool because you can control distance, angle, falloff, even XYZ. Dirt is great.... Just don't confuse it for an actual lighting pass.

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Christopher P Nichols