Is Ambient Occlusion really necessary?

This is my latest blender creation. ( Inspiration: Blender Compositing breakdown by Timmy).
I’ve a slow computer and I’m very impatient too and prefer fast renders. So, for this scene I used Blender Internal(as usual) and No GI as it takes a long time to render with AO & Env Lighting enabled. So, my question is that is it really important to have AO in your scene. If yes than suggest me some way to fake it. Also, give me feedback about the render. Thank you.

Blender internal doesn’t do GI so I am not sure what you are talking about there. However if you feel that an AO pass is too slow then you are presumably using way too many samples. On my (multiple) computers I hardly get any slowdowns at all from either AO nor environment lighting.

As for ways to fake it. If you have a scene where nothing is animated (moving or deforming) you could bake dirty vertex colors (Tutorial here) and use that as an AO map.

Also I do not see any render.

Sorry to say it but if you are very impatient 3d might not be right for you.

If speed is desired ditch blender internal and use yafaray the resurfacer there is much faster incl. AO.

What he refers to are the approximate occlusion modes in bi and the env light with raytracing

I have to agree with cekuhnen on this:

And I agree with NinthJake:

I don’t see a render, perhaps your post count is too low to attach images…

I’ve also had 3-4 computers rendering for 3 weeks solid to produce just 10 seconds of video.

If you want to render faster, spend money and buy faster computers. It’s a simple trade off, the more muscle you put into the job, the faster it gets done…


hey guys! thanks for such quick support, I was thinking to check back after a week! And, I had some problems with this forum coz I’m new. I had to google search my own post, seriously! But now I’ve managed to upload the render. Please give your valuable tips & critiques.

And my question here is that what is the role of AO in a scene, like when I see at AO pass, its just soft shadows at crevices, corners etc. I think it can be easily replicated by simply setting up lamps around the scene and you get your model lit up with soft shadows. So why enable AO and waste time. Sorry guys, if I’m unable to make you understand what I’m saying. Thanks again.

Yeah, sorry I though Env light + Amb Occ= GI. My bad. Thanks for the tutorial link.

If you’re happy with the result, then no, you don’t need it. The whole point of AO is to help approximated GI algorithms (final gather, irradiance caching), because they need many samples to give you details (which costs a lot of time). So the workflow is - tune your GI to get a result without splotches and then add the fine details using AO. But blender internal’s GI is very poor, so the more you might want to use AO.
On a side note - simply multiplying black and white AO over the whole image is wrong, but that’s what’s usually done.
Finally, brute force pathtracers such as cycles, don’t need AO (in fact it’s something redundant for the GI, because it has all the detail due its brute force nature). So using AO in cycles is more or less just a matter of artistic taste.
For further reading check this

Suggestion to fake it, and render it in less than one second.
SSAO, Screen Space Ambient Occlusion.

I would rather do the pass in Cycles, get it right. But if time is limited and you’re done with the image, clone the .blend file and flip to game engine and apply the SSAO GLSL shader to the camera.

thanks friend, that explaination was really helpful and that article link was great too. I think I’m getting closer to my answer. For now, I think I’d not give much thought to AO and simply lit up my scene the manual way without any automation. that’ll will be great for learning lighting too. also if you can give your opinion(and everyone around here) about the render, is something missing or something is way over, things like that…

bake the ao…
big companies do this too…

only the amateurs does re-render everything and crying of the slowness :slight_smile:

well yeah, I looked forward to baking ao but the problem was then I had to bake an ao texture for every single object in my scene which is not a solution for bigger scenes. I tried texture atlas to bake the whole scene into one single texture and then apply using the atlas UV, but then I lost my original UV for battery texture. I don’t know if I’m thinking & doing it right. Do suggest me if you’ve a solution to this.

just bake AO with few samples… and then use blure with vectores in comp.

AO is used in archviz exteriors to add shadows around small objects(say window frames),so you can use lower quality GI(photon mapping) -search archviz ao tutorials.-this is in general, not specific to Blender the above render the difference wont be much.AO pass layer is used in multiply mode(@20% opacity) over GI render.

I think you are supposed to multiply it over the ambient pass and than add that result to the rest of your passes, I don’t think you can get an ambient pass from Blender though. cdog had the link to the masterzap tutorial that explains it all.

That render looks real to me, but I’m not an expert in rendering nor lighting. In any case, I really like it! As for whether AO is essential…not sure really, but I’m easily impressed and love the results of using AO - especially after spending weeks working on a model in a dull(by comparison) view port.

Just some advice for entering the field of CG: Learn to budget for your hardware and upgradges. There are tricks such as baking which can help speed things up, but in general we are pushing our hardware far beyond what its meant to do. Using a low spec computer is like using a Smart car instead of a Pick up truck for hauling heavy goods: you need space and power. Rendering is probably one of the most demanding tasks you can put on a computer, so investing in a good computer is recommended. As this 3D stuff is expensive, it pays to spend some thought on a long-term savings plan of some kind.

Anyway, its just a thought. Out of curiosity, what are your system specs?

hi tyrantmonkey,i have written about one workflow for archviz,if you notice i start my reply “AO is used in archviz exteriors…”

It’s not about what style of rendering you are doing in terms of archvis, animation etc. Most people tend to multiply AO over the whole render or other passes but if you are looking at the correct workflow than its just with the ambient light.

Old school render engine have an ambient light (BI has this) which is that omni direction shadowless light and that is what you multiply your AO with. The occlusion of the directional lights in your scene is the shadow the cast.

That link like I said explains it better, it explains where that ‘dirt’ in your render comes from if you multiply it over other passes.

Moved from “General Forums > Blender and CG Discussions” to “Support > Lighting and Rendering”

It also might be worth noting that, technically speaking, AO is already faking it.

thanks Sam for the appreciation, and for the tips too. my system specs are really poor, its a pentium 4, no gpu, 2gb ram, takes over an hour to render this.