VRED 2022.3 Ambient Occlusion discrepancy

[MannaTheBerserk]

Hi everybody!

I have a problem with the ambient occlusion render pass.

It is completely different from the AO that comes out of the "Bake Light and Shadows" tool/window.

The render pass looks like a chalk render, which has nothing to do with real ambient occlusion.

Please have a look at the comparison pictures below, so you can have a better idea of what I am talking about.

Thank you very much!

Mauro

[michael_nikelsky]

That looks correct. The AO in the baking module has nothing to do with the AO render pass. The baking module allows you to set a distance for objects to include something. The render pass always uses the full occlusion of an object, independent of any distance. It is a complete fake pass anyways that is only useful for some artistic reasons I guess, it does not have any physical basis and in a full GI render should not exist anyways. It is just a pass that allows you to make regions in your image darker in a composite, for recreating the image you see in the viewport it is not used at all unlike the baked AO. In my opinion you should just forget this render pass exists since all it does is make your renders slower.

[MannaTheBerserk]

Hi Michael,

The Ambient Occlusion pass is used all the time in VFX, to produce punchier contact shadows. All the render engines I have used so far (V-Ray, Arnold, RenderMan... ) can produce either a clean AO pass, with no grey where the white should be, or a chalk render, like the one that comes out of VRED render pass.

In VRED I have no options/parameters to tweak, when it comes to the AO pass.

A render without a proper AO pass looks dull, flat and, despite it not to being physically accurate, wrong. That's why I need to be able to tweak it, in order to have something similar to the baked version (which is still a lot worse than the AO pass coming from the render engines mentioned above), and achieve the contact shadows and the cavities that would otherwise be unrealistically lit (e.g. doors shut lines, tyre tread cavities and dents, walls corners... And so on and so forth).

The render pass makes the render slower only because AO is not part of the beauty, unlike the other passes, but it is needed and it is the most common thing you would see in a standard VFX comp job.

Yes it's for artistic/aesthetic reasons, and not "just". My job as a Viz artist is to make pretty renders and animations. An AO pass is one of the "tools" that helps achieving exactly that purpose.

Besides, it's there, and I would have liked it to be useful the same way it is in other software (unfortunately I am stuck with VRED for this particular job).

If I should forget about it, then the VRED developers should just get rid of it. No reasons for it to be there in this state.

Thanks for the feedback.

Best regards

At the end of the day this does not solve my problem. 

[michael_nikelsky · Accepted solution]

I have created a feature request for having a distance control for the AO pass. 

The gray look in your example surprises me though but I guess that depends on how much of the scene is actually occluding the sphere. For now I would just recommend to adjust the levels of the AO-pass in the compositing tool.

Kind regards

Michael

[MannaTheBerserk]

Hi Michael,

You might be even more surprised, knowing that there was nothing occluding the sphere from the camera view.

The only objects in the scene are the two planes (three if we count the floor) and the sphere itself, and that's it.

Thank you very much for the feature request, that will be super useful for future projects.

I have used levels (and curves) to adjust the AO pass, though they reveal quite a bit of noise. I guess I should increase the samples, in order to get rid of that noise?

Best regards

[michael_nikelsky]

That is indeed strange, it looks like tone mapping is applied to the pass for some reason, no idea why that happens, if you render out passes all the auxiliary passes should not get tone mapped. What rendersettings are you using?