How do you implement your Ambient Occlussion Pass?

[TSuess]

According to Master Zap I've been doing it all wrong.

 

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

 

Can anyone tell me exactly how they've adjusted their workflow to eliminate occlusion from appearing in direct light? More specifically, how would one implement this solution for an interior scene? Should we all be running a direct pass, an ambient pass, and an ambient occlusion pass? If so, what is the best way to do this?

 

I need the "Idiot's guide to the proper implementation of Ambient Occlusion".."For interiors"

Edited April 26, 2011 by TSuess

[TSuess]

Based on the total lack of replies to this post I can assume one of two things. That either no one cares and this isn't really an issue or Zap is wrong. Zap contends that ambient occlusion does not occur in direct light. His solution to this problem is one I still don't fully comprehend (see link above). If he is in fact correct then wouldn't a simpler solution be to turn off FG and GI, run a lighting pass in Max, invert and use as a layer mask on your AO pass? I'm still not convinced that AO does not occur in direct light. Maybe I need to better understand what he means by direct light. If I placed a lightbulb in a white room and turned it on would all for walls the ceiling and floor be considered to be in "direct light" In this scenario the effect of ambient occlusion would still be apropriate. The corners should become slightly darker then the standard lighting solution would convey. I understand that Zap's post is 2 years old. I'd be interested to know his thoughts on this subject today. I'm also very interested in the opinions of other Arch Viz professionals. Anyone, Anyone, Bueller?

Edited April 26, 2011 by TSuess

[RevitGary]

I render out a targa image and in render elements tab I add a raw ambient occlusion pass.

When the image is done rendering it creates an AO pass as a separate targa file.

I apply this as a layer "multiplied" in photoshop elements.

[Alex York]

multiplied AO is no good, because "real" AO will be a bounce of coloured light, not just pure black (which is what your multiply operation is doing".

 

I always use AO right inside MR's materials, with the correct colour being thrown around. It's slower to render beauty passes but looks far better.

[RevitGary]

Maybe I am doing something wrong?

I have AO turned on with materials also.

 

My raw AO passes are typically just dark thin crevices in the image.

 

It just bunches these back with a nice dark.

[John Dollus]

zap is correct. As most of us apply the pass, it's behaving like more of a dirt shader than a true AO pass. i also subscribe to Alex's method of including it within each shader as I feel it gives me more control. If the deadline is especially tight (more and more these days), i'll crank it out as a quick dirt pass but I'll always paint a quick mask in post so it's not so globally overwhelming.

keep in mind that the Ao technique was developed as a fast calculating approximation of true GI in the presence of raytracing and not really intended to be used in conjunction with GI methods.

[TSuess]

I just posted a tutorial on how to incorporate AO in your composition as a seperate pass and still account for direct light. I find it much easier than managing your AO settings in each individual shader. Check it out here: http://www.renderededge.com/2011/06/ambient-occlusion-and-direct-light.html