Definitive Guide to VRay and Render Passes

[Skip Jones]

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.

[Christopher Nichols]

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

 

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/phpBB2/viewtopic.php?t=13818

 

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

[martin walker]

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]

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 !

 

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.

[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.

[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.

[Justin Hunt]

AO in interiors can add a good feeling of depth and grounding to object, if use subtly. AO can also bring back lost detailing in areas are in deep shadow or are highly reflective.

 

There are some AO shaders that do colour bleed, but only with one bounce. I did come across a website where there were some XSI shaders that did this, I would have to do a bit of tralling to find to though.

 

JHV

[martin walker]

Christopher / Andrew, thanks for your explanation. I was getting the definition of AO confused. I was under the illusion that it was simply a GI calculation using a HDRI or env colour and not lights.

 

This leads me onto another question.

 

I render my exterior scenes with a HDRI or just plain (slightly blue) env(skylight) colour . I get little noise and rendering times are very quick....Ive also tried the same for interiors and get decent results.

 

However if I introduce vray lights, my rendering times increase, I get grainy results....

 

am I missing something, or is it better to avoid using v-ray lights for a global / ambient illumination, and just stick a direct light in here and there to get some shadows ?

[Christopher Nichols]

AO in interiors can add a good feeling of depth and grounding to object, if use subtly. AO can also bring back lost detailing in areas are in deep shadow or are highly reflective.

 

There are some AO shaders that do colour bleed, but only with one bounce. I did come across a website where there were some XSI shaders that did this, I would have to do a bit of tralling to find to though.

 

JHV

 

An AO shader that bounces light is not an AO shader. As soon as it bounces light it is GI. As you noted you find that AO adds depth etc... you also mention XSI, MR, etc... All of this points to the fact that you are using AO to add the illusion of GI. Vray can do super high detailed GI with plenty of contrast and detail in all the corners where there is no need to AO. It can do full GI faster then most rendering engines can start to even do AO. The pipeline that you mention Justin starts to breakdown what is great about Vray. That is that it can do all the lighting correctly without the use of an AO hack. In fact, vray even has a "detail enhancer" in the new build that adds an extra amount of detail and humpf to the edges and corners by applying an extra brute force GI (not AO) with a radius falloff to the Irradiance map.

 

Now... if you want to use an AO style shader to mimic dirt by darkening corner... have at it. But don't confuse it for lighting. Dirt can add depth and grounding as you mentioned, but it is not lighting.

[Christopher Nichols]

Christopher / Andrew, thanks for your explanation. I was getting the definition of AO confused. I was under the illusion that it was simply a GI calculation using a HDRI or env colour and not lights.

 

This leads me onto another question.

 

I render my exterior scenes with a HDRI or just plain (slightly blue) env(skylight) colour . I get little noise and rendering times are very quick....Ive also tried the same for interiors and get decent results.

 

However if I introduce vray lights, my rendering times increase, I get grainy results....

 

am I missing something, or is it better to avoid using v-ray lights for a global / ambient illumination, and just stick a direct light in here and there to get some shadows ?

 

If you are using GI to get your ambient light yes... there are time when you want to use and Vray Light in dome light mode with and HDR (in vray 1.5 currently), can work as well but not in the cases you are outlining... meaning they are slow. I outline the techniques you want in my interiors DVD.

[AJLynn]

I usually use a direct or spotlight light source for a sun when needed, though a Vray Light can also be used - there's a section of Chris's exteriors DVD where he does that and it works out well.

 

Chris- am I remembering wrong or in that DVD do you make a comparison between a GI pass and an AO pass in the highway scene? IIRC it seemed like it could lead to a bit of confusion for people not already familiar with AO vs GI.

[Justin Hunt]

Chris - I know that AO isn't lighting, I never said it was.

 

You are also wrong with the AO shader that does colour bleed, it isn't GI. Basically what it is doing is reading the colour of the surfaces the samples are hitting and returning it back to the AO shader. It isn't a lightray, ie the samples do not originate from a light source, it originates from the AO shader. Think of it acting in a similar way a reflection ray works, only not as accurate or time consuming as it only reads the difuse colour of the hit object. I know I havn't explained myself very well, let me find the web site, it explains it much better.

 

Yes AO is a hack. I have seen plenty of Vray GI render where objects have the apperance of floating, with a little AO - Note I said LITTLE - those objects are grounded. It is just an other way to get detail without the need for lenghy brut force GI calculations.

 

I have been playing with AO in the reflection slot to give the effect of the reflection changing from sharp to blurry according to the distance of objects to the reflective surface. By using AO distance settings I can control how quickly the transition happens. It does add a heap to the render times but helps eliminate the "blurry all over" look that has been used to death laterly.

 

JHV

[Christopher Nichols]

I hear you Justin... but philosophically, completely against you... let me explain. What you are trying to accomplish with AO is what you should be doing with GI... The reason that objects "float" in some Vray renders is that the GI settings are too low. They are not picking up enough samples near the edge. So you suppliment it with some AO. I hate that because it is like you came so close but gave up with AO. Same with the single bounce of light. I think that Vray's GI is plenty fast enough where you don't need to do that, and that you can get a lot more just my increasing your GI quality instead of creating the extra pass. That is why they created that "detail enhancer" setting in the new Vray to get some extra samples right in those areas where and AO shader would get the detail, bit get it correctly with full GI instead of a fak AO. Normally I woudl simply increase the Irradiance map setting, but that allows more freedom. A world where AO is not needed is a better more accurate world of true global illumination, and I will not rest until people realize that....

[Christopher Nichols]

I usually use a direct or spotlight light source for a sun when needed, though a Vray Light can also be used - there's a section of Chris's exteriors DVD where he does that and it works out well.

 

Chris- am I remembering wrong or in that DVD do you make a comparison between a GI pass and an AO pass in the highway scene? IIRC it seemed like it could lead to a bit of confusion for people not already familiar with AO vs GI.

 

I did... I think I made a similar point that I am making here... am I not?

[Justin Hunt]

I understand your view, I am just giving an other way to "skin a cat"

 

Although I dont see it as "Giving up on GI" but rather enhancing GI, just in the same way that we enhance our renders in Photoshop, or is that cheating too?

 

JHV

[Christopher Nichols]

I understand your view, I am just giving an other way to "skin a cat"

 

Although I dont see it as "Giving up on GI" but rather enhancing GI, just in the same way that we enhance our renders in Photoshop, or is that cheating too?

 

JHV

 

Yeap... but I say, enhance GI with better GI (higher detail), not with AO. The cost of doing so in Vray would be the same. But that is my philosophy, as an artist. Everyone has their own set of brushes.

[martin walker]

yeah, think there is a definite confusion / overlap with where AO stops and GI takes over !

 

The AO demo on your DVD Chris, led me to think that AO was simply the first GI "bounce" which included colour bleed / contact shadows etc... but its probably me being stupid rather than your example !!!

[Justin Hunt]

To be fair, I dont use AO with Vray, only MRay.

 

I was talking more in the defence that AO does have a use and benifit when the cost of a highly detailed GI solution is too great.

 

JHV

[jbrckovic]

Hi to all!

 

This thread has interesting title about render passes, but finished with AO. This multipassing is rather interesting to me especially after Christoper Nichols' sentence "Render once, composite many."

I have some questions:

1.Is there any possibility to tweak lighting in composition. Let's say we have 3 lights in scene. Is there any possibility to change each light's intensity and maybe color, but not to render same scene 3 times. (Thinking aloud) Or is it possible to render with high settings once, and to shorten rendertimes render without reflections. But then in composition there will be wrong reflections...

2.Second question is: Which tool to use? AE has sweet UI and lots of plugins but is it capable of composite such a complicated situations?

[Randy liddil]

 

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.

 

 

pretty interesting comment on AO but the company that I'm at has never used it for faking the GI look. Instead, there are several really good ways to make an AO material without using the standard vray dirtmap to use in photoshop as a "linear burn" or "multiply" layer effect which in turn brings out some really good depth and shadow. After this is done an inverted specular pass can be rendered and used as a "linear dodge add" in photoshop which give a ton of control on highlights. Unfortunately, in the 3d world that i'm in, everything is due in a very fast time frame and these passes work really good to get fast control over the renderings rather than trying to do it all in 3ds max.