Ambient Occlusion not working properly (too bright)

[AndreasResch]

Hey guys,

I have an odd problem with ambient occlusion. The scene looks great in the preview rendering as well as the actual rendering. As soon as I turn Ambient Occlusion ON in the World settings, the scene gets very bright - both in the preview rendering and the final rendering. I have no clue why that happens.

Here’s a quick comparison of the same scene with and without Ambient Occlusion ON.

I use Cycles as renderer. The scene uses a simple HDRI for lighting. AO settings are nothing special - Factor is at 1 and Distance is at 5mm. Blender version is 2.75 Stable.

Maybe someone can clear this up for me.

Thanks,
Andreas

[IkariShinji (Thies Schulz-Holland)]

Perhaps you know ambient occlusion from Blender’s Internal renderer:
Cycles AO is not a “multiply” AO, but an “add” AO. If you want to use AO to just darken creases etc., render out an AO pass and combine it with the beauty pass in post. Using a much larger AO distance might also help (more in the several meters range rather than in millimeters).

[AndreasResch]

@IkariShinji

Perhaps you know ambient occlusion from Blender’s Internal renderer:
Cycles AO is not a “multiply” AO, but an “add” AO. If you want to use AO to just darken creases etc., render out an AO pass and combine it with the beauty pass in post. Using a much larger AO distance might also help (more in the several meters range rather than in millimeters).

Thanks a lot.

So the Distance value applies to the render pass even if the AO checkbox is not checked - correct?

Cheers,
Andreas

[IkariShinji (Thies Schulz-Holland)]

Sorry, I had feared that you might misunderstand me because of my bad wording. And here we are…
AFAIK the AO pass has no connection to Cycles’ AO world settings.

What I meant was: You can either…
a) …use an AO pass without the world AO settings or, if you don’t want to do that,
b) …use the world AO, but with a much larger distance setting. It will still be (too) bright, but perhaps not that overpowering.

[marcoG_ita]

Sorry, I had feared that you might misunderstand me because of my bad wording. And here we are…
AFAIK the AO pass has no connection to Cycles’ AO world settings.

This is wrong

@AndreasResch

So the Distance value applies to the render pass even if the AO checkbox is not checked - correct?

Yes, distance affect AO pass even if World AO is not in use.
If you want to use World AO directly in your render and avoid overbright scene, i’d suggest to lower the Factor to 0.1 or even 0.05, not 1.0 absolutely.

[IkariShinji (Thies Schulz-Holland)]

@marcoG_ita

Yes, distance affect AO pass even if World AO is not in use.

Sorry, but I can’t seem to find any information about this - neither in the Blender manual nor in the wiki. Where is this documented?

[marcoG_ita]

Don’t know about the manual. You can test this in few seconds, turn on AO pass, keep World AO disabled, render 3 times with different AO distance, lets say 0.1, 0.5 and 1.0… AO pass will reflect that distance you’ve set.

[AndreasResch]

@marcoG_ita

Don’t know about the manual. You can test this in few seconds, turn on AO pass, keep World AO disabled, render 3 times with different AO distance, lets say 0.1, 0.5 and 1.0… AO pass will reflect that distance you’ve set.

Thanks for the confirmation, Marco. There had to be an AO setting somewhere and as the input in the wolrd section is still active even when the checkbox is unchecked, I thought that must be the setting responsible.

Cheers,
Andreas