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Edit:

Recently I've been rendering a fairly geometry dense indoor scene, with one window. I was finding that even at 524 render samples, the scene was grainy, and also really REALLY slow!

I had a portal over the window and my world resolution was at 2048 (supposed to decrease grain) I was rendering with 3 diffuse, 4 glossy, 8 Transmission, 0 volume and a total of 8 max bounces and 4 min.

The render time was around 7 minutes per frame (grainy) and increasing rendertime wouldn't have been an issue, provided this wasn't an animation. However, I remember a while back, on a "speed up cycles" vid, that AO bounces was mentioned?

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    $\begingroup$ Would be nice to add pictures, imho this post deserves it, would make it awesome. $\endgroup$ – Jaroslav Jerryno Novotny Jun 17 '18 at 21:33
  • $\begingroup$ @JaroslavJerrynoNovotny Done :) $\endgroup$ – Rich Jun 19 '18 at 1:13
  • $\begingroup$ I sometimes render interior scenes with 15 000 samples... 7 minutes?.. That's like making ONE cup of coffee. I would kill for render times like that. Try the Intel AI denoiser from 2.81 experimental builds. It works miracles. $\endgroup$ – Martynas Žiemys yesterday
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Scene Full render 1080 no AO bounces full light samples

So, I went into "simplify" in "scene properties" and added 1 AO bounce. I went from 15 minutes a frame to 47 seconds with NO grain! The catch?

AO Bounces added

An AO bounce, takes light from the world background (I think) and adds this into the scene (interior or not) It also, removes all reflections from glossy or metallic surfaces and replaces them with the world background probe/map.

World probe shows in mirrors

This Didn't help, considering my whole animation was based around a showcase for a product that you use on a MIRROR.

The fix?

Go into the "world Properties" enable "AO" and increase the Distance until these reflections disappear. Then back to scene and increase the light bounces for AO, until your scene looks right.

AO enabled 10cm

changed to 3.55m

You will find your scene is a lot more exposed, however, if you use the "filmic" colour management, and set it to one of the higher contrasts, and then render in a HDR format, you can reduce the exposure and keep the correct contrast ratio.

Changed AO bounces until probe disappeared from mirrors

Full render down from 17mins to under 4 no denoise

Now, I didn't stay at 47 second render time per frame, however I did cut if from 15 minutes, to 4 minutes. Which, is a massive difference!

Full GI post FX Denoise

I hope this helps anyone with a similar issue. Please remember, this is only useful for indoor scenes! an outdoor scene won't have the same noise issues, and fiddling with the AO, will massively increase the world background becoming oversaturated.

If you couple this hint with the Denoising feature, you will get a really good looking render, for a third of the time.

enter image description here

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  • $\begingroup$ To control the brightness, bring down the value for ambient occlusion. The default 1.0 is too high. $\endgroup$ – cegaton Jun 19 '18 at 12:40

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