Ambient Occlusion

[Infrared digital]

Hi

Just wondering what is the best way to render the final image and an AO pass at the same time ?

Up until now I have rendered a completely different model with a dirt map on it and composited to get the effect I need.

Thanks

N

[Neilg]

Use it in the diffuse of your main materials - Put your bitmap in the unoccluded slot, then copy it into the occluded and make it darker with the bitmap adjustments.

You can throw in a few nice tricks with this method too - as an example, a standard grass bitmap blending into dirt/soil near the edges, but using another dirt map in the radius to make the blend a bit less uniform.
You can also do multiple levels of blends with this by putting another dirt with a smaller radius in the occluded slot - say a light concrete blending into a dirty one, then going into a streaky moss which only affects the z/vertical axis.

[Da_elf]

i think the AO pass is to allow him to be able to tweek in post. your method doesnt allow that

[Neilg]

I assumed this - " final image and an AO pass at the same time " meant he wanted to move away from that.

[Infrared digital]

Thanks for the suggestion on the dirt map which is excellent for application to individual geometry but, I want to apply AO to the entire model so - is it possible (and effective) to do this with the final rendered image or is it better to render it out as a render pass in the Render Elements and composite it ?

I am working on an animation so, anything that flickers is out the window.

[percydaman]

I think you need to just bite the bullet and render it out as separate pass. You can of course use the override option. But Ive found better results from having a few different vray dirt mats applied with some different settings to different objects. Vray dirt that looks great on your walls look crappy on your small objects and vice versa.

[tct70]

Sorry to butt in, but I don't really get how to use AO/Vray dirt. I understand what it is used for, but it's the actual process that escapes me. Do you render your scene with very low GI settings and then use AO passes in post - if not how do you light your scenes?

Thanks.

[percydaman]

I use vray dirt as an occlusion pass. IE there to give additional shading and detail. It doesn't require GI, in fact you wouldn't really want it to. Theres more then one way to set it up. One way is to take a standard mat, give it white diffuse and set it 100% self illuminated. Then just stick the vray dirt in the diffuse slot. Adjust parameters to suit. Itll take some testing on your part to get the finer settings.

Oh and I guess technically you wouldn't have to put set the diffuse to white since you have the map in there. I always set falloff to 1.0 as well, otherwise I dont like the way it looks where say to walls meet at the ceiling.

[Neilg]

Thanks for the suggestion on the dirt map which is excellent for application to individual geometry but, I want to apply AO to the entire model so - is it possible (and effective) to do this with the final rendered image

Yes. Pretty much all of my materials have a vraydirt in the diffuse, and you can control it individually to get more control where you need it.

Although I gave the example for individual objects, I meant for you to use it on everything.

Probably not something you want to do on a scene already finished at the rendering stage...

[tct70]

@percy

So, if I'm correct, you rensnder as normal, and then use the AO pass in post for extra detail.

[percydaman]

yup. It gets multiplied over your beauty pass at comp time. I usually set its opacity to 50ish and frequently tint it slightly to warm it up.

[tct70]

Thanks very much!

[Infrared digital]

The AO pass applied in the way mentioned can completely transform a render - thats why I am interested in using it in an animation.

[m_hinks]

I'm very interested in using this method too.

[Arkitec]

Ive seen this done with Mental Ray.... which also has an override materials.... which seems awesome......

But how do I do this in Vray as an element? or am I totally off base.

The only thing I see to do is go to the Vray - Global Switches, set the override mtl: assign a vray material and place a VrayDirtMtl in the diffuse slot and render.....

Is that it?

Assuming this is the case, I then would have to render out an entire irrmap sequence for an animation and then comp it in?

or for single images, just comp in Photoshop with multiple setting under layers?

Am i close?

TIA,

Arkitec