Ambient Occlusion Rendering

[richard_rosenman]

Hi guys;

I'm trying to find more info regarding Ambient Occlusion Rendering, particularly for 3dsmax. Anyhow have any info/ideas?

Thanks,
-Richard

[J_Bug]

Hi Richard,

Here is a link that I got some good direction from. Not specifically MAX though...

http://www.andrew-whitehurst.net/amb_occlude.html

and Seraph3D gets into it about half way down this page.

http://www.seraph3d.com/tutorials/compositingtut02.htm

--Jon

[dbuchhofer]

Well, Ambient occlusion is just a skylight with 1 bounce.. you probably want to get more into the Baking side of it?

I've got a fair book at home from a course Renderman in Production from siggraph either 2001 or 2002, but can't find the info online at the moment.

[cocolas]

Well, Ambient occlusion is just a skylight with 1 bounce.. you probably want to get more into the Baking side of it?

I've got a fair book at home from a course Renderman in Production from siggraph either 2001 or 2002, but can't find the info online at the moment.

if you could tell us the name of that book, I would really appreciate it....

paul.

[percydaman]

As its been said before, ambient occlusion in max is kinda repetitive as it has several renderers capable of very quick native skylight. One thing to keep in mind that unless you use final gathering or something like it, its hard to get any color bleeding, which is fine for the simple exterior tutorials you see alot of these days, but for more complicated indoorlike scenes with alot of variation in colors it doesn't work as well. (sorry for run on sentence)

Ive always been more intrigued with the use of occlusion mapping used in conjunction with reflection mapping. Probably not as important these days as raytracers are so much faster, but I still remember back when raytracing was prohibitive to much more then still images.

Anyways, correct me if im wrong

percy

[dbuchhofer]

Hola Paul, its a set of course notes for the course RenderMan in Production..

http://www.siggraph.org/s2002/confer...ses/crs16.html

Doesn't appear to have been put on the Transactions dvd though..

http://www-cg.cis.iwate-u.ac.jp/~fre...rse_notes.html

Its course 16 from 2002.. I recommend the first portion to it to anyone who wants to understand the inner workings of CG a little better.

[cocolas]

thanks much Dave!!

I'll take a look....

paul.

[Seraph135]

As its been said before, ambient occlusion in max is kinda repetitive as it has several renderers capable of very quick native skylight. One thing to keep in mind that unless you use final gathering or something like it, its hard to get any color bleeding

I don't believe you can render colorbleeding as a part of your ambient occlusion pass. GI/skylight and ambient occlusion aren't the same thing, though they do look very similar in most cases. Thats why GI renderers can be used to get a "good enough" kind of ambient occlusion. As far as I'm aware only Renderman and Mental Ray are capable of shader based ambient occlusion at the moment. It requires a special shader built specifically for it.

Tim J

[richard_rosenman]

Hey Seraph135


What is the specific purpose of the shader? How does it work and how is it different from rendering GI image on white with 1 bounce?

-Richard

[Seraph135]

http://www.cgtalk.com/showthread.php...ient+occlusion
http://www.andrew-whitehurst.net/amb_occlude.html
http://www.cgtalk.com/showthread.php...5&pagenumber=1
http://zj.deathfall.com/depthbasedOcc.htm

There are several different ways to do it. The shader based version of ambient occlusion I was refering to is really like a dirt map. Its more of a where would dirt settle kind of approach as opposed to where would light be occluded. The version ILM invented was (someone correct me if I'm wrong) basically a skylight. The information was just stored in a shader. Its also used in combination with a bent normals pass, which to be honest I'm still trying to figure out how it works. :P

Tim J

[GonMAX]

As student of renderman, and user of prman, In my opinion describe that ambient oclussion is a simply skylight with 1 bounce is a very rough description, and also a very rough use of this technique.

Ambient oclussion is more complex than that.

PS: I prefer Vray aproach

[thethule]

As student of renderman, and user of prman, In my opinion describe that ambient oclussion is a simply skylight with 1 bounce is a very rough description, and also a very rough use of this technique

GonMAX, could you elaborate?



Marc

[zasid]

I think post this question at CGarchitect.com

Hi

I suggest to post this question at CGarchitect.com forum I think there u can get some close answers too.bye

[Psy]

This is an interesting topic of which I would like to post of my experiences with max and ambient occlusion. It can be done w/o using vray but realistically, for 3dsmax at least, it's a pain in the ass.

Here's an image I did using AO in 3dsmax


It seriously took about 4 different renders and of course, some photoshop layering to get that. Maybe if you are in desperate need of AO for animations it is worth your time to do it (using AE), but for just still images, I personally think it is a waste.

[kedojo]

I used XSI/Mental Ray for awhile, and came across a pretty useful occlusion shader written by Daniel Rind (it was featured in a really good ambient occlusion tutorial in Highend MAG: issue 4 2004). This was directed at XSI users, but it's general enough that you might find the info useful.

From what I understand, GonMAX is correct - occlusion is quite a bit different than a 1 bounce skylight. The occlusion shader enables the material to cast rays from various points on the surface in order to collect distance values to the nearest object. The smaller those distance values, the darker the pixel is shaded and vice versa. Shading is then based on the proximity of objects, as opposed to being based the number of skylight rays that hit an object (as in a 1 bounce skylight).

The "look" is similar to a skylight which may create some confusion, but the nice thing about occlusion is that you can scale the shading and proximity values to create the desired shading "falloff". This can be useful if you're rendering is passes - you could create a non-occlusion GI pass with very low render settings for speed (which gives you somewhat washed out, non-defined shading) - then overlay an occlusion pass which is setup to darken only the very close proximities thus faking the typical hi-quality GI rendering.

HOWEVER - I've found that if all your doing is a photorealistic GI rendering, don't bother using occlusion - it's easier and just as quick to use VRay's typical GI parameters.

BUT, occlusion shading can be extremely cool for NPR stuff, such as creating a dirt-like effect (in the crevices of detailed models) or simply adding subtle depth to objects...I recently saw a great spot that PSYOP did - it was a promo for their company, using these furry little ball-like animals with occlusion - it almost gave the clip a dreamy watercolor effect.

In any case - hope that helps...I'm no expert though!