Mental Ray Vs Vray ambient occlusion

[stayinwonderland]

So I'm just getting into both Vray and Mental Ray in that order. I like Vray but MR is that bit more standardised and also works with vue should I need some scenery/foliage.

 

I had learned to use Brazil back in the day and found that a few clicks brough some really nice dense shadows. It was great for that overcast ambient occlusion look.

 

In my recent studies of VR and MR I found that such an effect had to be earned and didn't just come as standard. VR has an option to enable it and play with it which is nice. MR however needs to be kind of hacked to get it to work - as though it's an after thought.

So I just wondered what people's opinions were on this?

Focusing on MR, is it common for you guys to stick an arch+des material on every single object and enable AO? Or do you just stick an ambient light in the scene and turn off final gather? If so, does it ever look that stunning? Perhaps you have examples?

[LukeC]

Are you looking to render off an AO pass that you'll comp together in post or include all together in one single render?

 

As I generally render off a pass for comping in photoshop. I use both Vray and MR at work and to be honest I find both pretty much the same.

 

All my scenes are lit with a dome light and a direct or sunlight depended on the scene.

 

For Vray I use a vraydirt texture in a vray light material and adjust the dirt settings to control the size / intensity of the AO and MR I use an Ambient/Reflective Occlusion shader in a Mental Ray material as an override. Both of which with no scene lights on and my scene settings turned down for speed - you can find more detailed descriptions on google.

 

To be honest, I wouldn't consider the way of doing an AO pass as a make or break for either engine. I'd just go with whatever you find easiest to use. As a rough personal summary, I'd say Vray has quicker renders at the cost of a slower setup and MR has slower renders at the sake of making it a bit more simple/forgiving to the user. Its a much of a muchness really.

 

Not sure if that answers your question but its the first day back from the holidays so my brain isn't really in gear.

[stayinwonderland]

Thanks for the response. Good to hear that neither stands out as particularly better.

 

I guess I should use an example. Here are 3 renders:

 

[ATTACH=CONFIG]46485[/ATTACH]

 

This one was rendered using default skanline, a skylight with a target direct and a HDRI in the env map. I love the shadow detail in this and have spent the last couple of weeks learning Vray and MR to achieve the same result but to no avail.

 

[ATTACH=CONFIG]46486[/ATTACH]

 

This is mental ray with a daylight sytem. Can't seem to get a decent overcast look. If I use CIE in the skymodel, the image looks awesome when it's computing final gather, lots of thick detailed shadows, then they all disappear once the actual render completes.

 

[ATTACH=CONFIG]46487[/ATTACH]

 

Vray. Just can't get anything nice with this. I want the overcast look so set the sun to a large size (shrug).

 

So, you mentioned a dome light? I can't find a dome light in the light creation. I think this could be a key factor as I need a primary source of light coming from all angles and casting subtle shadows, PLUS a dim sunlight. Thoughts?

 

Cheers.

[LukeC]

Ah sorry, that was my fault. I wasn't thinking straight this morning.

 

For vray, if you create a vray light and change its type to dome - thats more what I meant. So basically i'd turn off all my lights (so that when it renders you get nothing but black - including any light materials), add a camera then add a dome light and adjust its intensity until I get the level of ambient light I wanted, then add a target direct light as a sun and adjust that accordingly. I use the dome light instead of the GI Environment slot in the Vray-Environment rollout in the render settings. I find it to be less noisy.

 

for MR, I find it easy enough to throw in a daylight system and if I want an overcast day just just disable the sun or reduce its multiplier. You may also need to adjust your exposure control to suit

 

Your vray render looks to me like it may have a gamma issue or possibly multiple lights.

 

Like I said before, a good trick I have found is to disable all lights and build your lighting up again from scratch working from biggest lights first (env then sun, then interior lights for example), that way you dont have any mystery lights playing around in your scene.

 

Hope that helps somewhat, I know my answers are a bit vague, just a tad busy at the moment

[Matt McDonald]

You might want to play with the relationship between the sun intensity and the sky intensity. That's one big thing that I notice, in your mental ray image the sun looks very intense relative to the ambient light.

[stayinwonderland]

Here are a couple of new renders using the dome light as suggest (thank you kindly).

 

[ATTACH=CONFIG]46489[/ATTACH][ATTACH=CONFIG]46490[/ATTACH]

 

This is vray with one dome at a multiply of 75, plus a sun at .2 (i left the sun out of the full render to try and see just how much shadowing i was getting from the dome). Also worth noting the feet had an invalid non VR texture in the full render so i wen to work on that (see foot render).

 

So, it's much better. But... would we not say that the shadows around the feet are still quite absent? The close up looks like it's floating :/

 

Suggestions on this?

 

Cheers

[Matt McDonald]

ok, so now you've got your overall light looking like you want it and now it's time to return to your AO questions. Ambient occlusion really should be applied at the shader level so that AO is applied to surfaces lit only with ambient light. If you apply AO across the whole render you are going to get AO in areas that, while physically close to one another are in direct light and should not have AO applied.

 

For some more reading

http://mentalraytips.blogspot.com/2008/11/joy-of-little-ambience.html

 

Because it's a pain to go through and enable AO on all your materials, and subsequently tweak them until you are happy, use an override material with AO turned on, tweak that one until you are happy with the results and then apply the settings to all your materials.

 

If memory serves, AO in V-Ray is applied as a texture so you can instance it throughout the scene making edits easy. For MR there are plenty of free scripts which will enable AO throughout the scene for you.

[LukeC]

Looking better

 

If your including AO in your render (or rather, not comping it in post), then like ELEVATION said then adding the AO into the material is a good idea. Peter Guthrie has a good tutorial on how to do this with a vray dirt texture

 

On a side note, with your sun (or whatever light you are using for your sun), make sure the shadow bias is set to 0. For some stupid reason this is still not the default in max. Anyway just check your light settings in the light lister (tools - light lister).

[stayinwonderland]

Ok folks, I got a few issues. Firstly, as a side note, it seems odd to have to make a rendering program add shadows in such a convoluted way given that my first render (done with skylight and scanline render) seemed to do it naturally? At least it seemed to.

 

So secondly, I kinda wanted to avoid the texture map approach coz it sort of locks you into that render engine. Wish there was a 'convert scene to mental ray' button. lol. But... if i must. My materials are mainly standard materials, is there a slot to place the Vray AO map in a standard material? Or will I have to scratch ALL my scene materials and replace with VrayMaterial?

 

I looked at the vray dirt article but not sure how this fits into what i'm doing?

 

thanks

Edited January 3, 2012 by stayinwonderland

[Matt McDonald]

There are "convert material to mental ray" scripts out there. Go to script spot and do a search.

[stayinwonderland]

Oh ok, that's really useful to know!

 

Right, so I put a vraydirt material into the diffuse slot of the ground plane and we have some occlusion happening! Is this what you guys meant?

 

[ATTACH=CONFIG]46491[/ATTACH]

 

So just wondering if this is the correct practise and also what's the best practise to put it into my other materials given they all have their diffuse slots taken up?

[LukeC]

hmm, given I do a lot of post work on my 3d, AO passes tend to be done in post so I may be missing something.

 

However, it does seem a bit silly to have to apply a vraydirt to every material to get a bit of depth in the image. Id say play with the Vray AO settings in the render settings dialogue (under Global Illumination from memory). That should apply things globally without having to play with the materials. Someone might be able to give a better answer

[aaronrumple]

I would either run a separate AO pass in Vray (You can do this manually with a material override or with some of the scripts out there.) Or I would use the built in AO feature of Vray. Running a separate pass gives you more control for mixing it in post production.

 

Using the built in AO probably means increasing it increased greatly for your desired result. Go to Indirect Illumination -> Ambient Occlusion -> On: 0.8 as a start value, Radius: Increase this to maybe about 1/4 to 1/2 the height of the model. For grungy architectural real world units, I'd set it to 5' to 10'. Up the subdivs to a higher value to smooth things out. 16 min, 24-32 are probably better. This of course burns in the AO, so if you want to change it, you will need to rerender.

[stayinwonderland]

Thanks for all the info guys. No one got back to me on how/if I should put an AO material on a non vray material diffuse slot?

 

Currently been trying some render tests using the vray dirt on the ground plane only and using GI ambient occlusion with some success. Would still love to get an idea for best practise though.

 

Either way, since starting this thread my rener looks a million times better. Check out what i have so far:

 

[ATTACH=CONFIG]46508[/ATTACH]

 

AO: 30, Radius: 8', Subs: 64

[Matt McDonald]

I wouldn't use the V-Ray AO on a standard material, I'm not sure why you would want to. The V-Ray Power Shader like the Mental Ray Arch & Design Materials are optimized for their respective rendering engines. You can use other material types (like standard) in your V-Ray or Mental Ray scenes but you might be opening the door to trouble.

 

Additionally, even if you put V-Ray AO on a standard material, you aren't going to get AO in scanline and Mental Ray isn't going to like it either.

[aaronrumple]

Thanks for all the info guys. No one got back to me on how/if I should put an AO material on a non vray material diffuse slot?

 

Currently been trying some render tests using the vray dirt on the ground plane only and using GI ambient occlusion with some success. Would still love to get an idea for best practise though.

 

Either way, since starting this thread my rener looks a million times better. Check out what i have so far:

 

[ATTACH=CONFIG]46508[/ATTACH]

 

AO: 30, Radius: 8', Subs: 64

 

I think that is headed the right direction....

[stayinwonderland]

Ugh, spent all night re-making the textures so i could put a dirt map on the diffuse of all the materials via vraycomtex. It's pretty much useless. Just puts dirty noise where there's shadow. But I would like a material that adds dirt wherever you like on a material, just to add a bit of grit.

 

No, I think I must conclude from trying: rending AO, material AO and render pass AO, that the render pass it probably the way to go.

[thomthom]

Id say play with the Vray AO settings in the render settings dialogue (under Global Illumination from memory). That should apply things globally without having to play with the materials. Someone might be able to give a better answer

I'm a V-Ray user - I've often used the GI AO for quick AO effect when I do not need to fine tune in post. Looking for similar effect in Mental Ray I came across this thread. Trying to process all the info, but do I understand it correctly that there is no similar function in MR?

[Fahad1987]

Hello

[Chris MacDonald]

I haven't had the time to read the entire thread, but for an AO pass straight out of VRay without any hacks all you need to do is add a VRayExtraTex render element with VRayDirt as the map in it. This will render out an additional VRayDirt pass along with your render. So no need to re-render with material overrides and so on.

 

I should probably add that VRay dirt is AO but on steroids, you can achieve so much more with things such as the x/y/z bias and being able to add noise maps and so on, especially useful if you are wanting to simulate dirt.

 

Here are a few things that may be of interest;

 

http://www.enrichpro.com/en/richdirt/index.html

 

http://www.peterguthrie.net/blog/2009/10/vray-dirt-tutorial/

 

http://www.ramyhanna.com/2010/04/creating-dirt-pass.html

Edited April 24, 2013 by Macker