Corona AO is different in version 10? Help!

[Julieta]

Hi all!

I'm very used to using Corona AO to apply dirt effect on different surfaces. So far it has always worked as expected.
However, ever since I updated to V10 I noticed it's not giving the same results and therefore, I wanted to ask you what it is that I'm doing wrong.
I attach the setup and the result I get. The result I want/expect from this operation is more of a gradient. I think you will all agree that it doesn't look realistic for dirt stains to have such sharp edges.

Disclaimer: In the picture I uploaded you'll see I checked on the "Use legacy color spread" but I get the same results when this is checked off. The only way to have a softer gradient is to adjust the direction offset in Z to less than 2, but that's not what I want since then I start having dirt on the other axis.

Thanks in advance for your help.

[hurrycat]

It seems to me like you have clamped the noise texture (min/max values). Are they set at defaults?

[Julieta]

Hi! Thanks for your reply.
I attach three images

1) my noise values for the previous render preview
2) the result I get with default noise map (without editing it)
3) the result I get with no distance map at all (this doesn't seem normal to me, or at least I didn't get these results before, I used to get a nice gradient)

Thanks in advance

[romullus]

Are you sure that AO with exactly those settings would look any different in older Corona versions? TBH i never use direction offset much greater than 1, because usually that leads to really bad results, much like in your pictures and that was true in versions prior to 10.

[hurrycat]

Yes this definitely seems off, on Corona 9 you indeed get a nice gradient. I don't remember having the Quality value, maybe it's in newer versions, but have you tried setting it higher?

Color spread can produce sharper results like the one you're showing, but I think you would need higher values than 0.2 for that.

I would lastly make sure the units and your geometry normals are correct, maybe try the AO on a different piece of geometry, and report back.

Also, it seems like there are 2 corona AO applied on the cube you're showing, one which seems correct at all the edges and one concentrated at the top face - maybe there is some geometry overlapping at your scene?
EDIT: I now noticed the Z direction offset - maybe try removing that!

[pokoy]

Julieta - for the devs to have something to work with, it would be great if you installed v9 again (uninstall v10 and all chaos components...), rendered a few examples (and saved the files), then installed v10 and re-rendered exactly the same example files, with identical settings everywhere. Otherwise it's difficult for you to make a point and for the devs to see the differences.

[Julieta]

Hi hurry cat, romullus and pokoy.

Thank you all for your replies. I'm pretty sure that I had always used values higher than 1 without having these sharp edges, however I can be mistaken and that can be the reason for these results. I don't know.  Unfortunately it's not possible for me to uninstall Corona now.
The file I'm using is a new file and the example is just a box with a generic Physical mtl with an AO on. So there shouldn't be any hidden geometry.
Anyhow, I'd like to ask you, in the attached example I set my Z offset to 1. How do you avoid this "lighter" effect on the sides? is there any way to do it, I feel this may feel fake in certain situations.

Thank you once again,

Julieta

[romullus]

Your pointed areas are certainly possible to get rid of AO without cranking directionality offset to unreasonable heights. You just need to experiment a little bit with color spread and/or ray directionality. Maybe tweak your noise map too. I'm attaching simple scene where offset is 1 and dirt effect is strongly prominent in only one direction.

Edit: you can also insert colour correction between AO and material and further tweak brightness and contrast and steer effect to your desired direction.

[Julieta]

Thank you very much Romullus, so kind of you to show me that!
Effectively, I must keep tweaking. Would you mind sharing the setting of the noise with me?

Thanks once again :)

[romullus]

There is a Max scene attached in my previous post, you can download it and see how the shader is set up.

[Julieta]

Ahh I apologize! I had not seen it. Thank you very very much for your help :)

[romullus]

You're welcome!

[maru]

Corona 9 and 10 running, literally, side-by-side. :)

[pokoy]

Corona 9 and 10 running, literally, side-by-side. :)

Great, thanks for showing this.

What's new in v10 about the spread parameter? I don't remember seeing this mentioned anywhere...

[TomG]

"Use legacy color spread – If enabled, the color spread will be computed as in the older versions (prior Chaos Corona version 10). However, in that case "quality" parameter will not only affect the noise but also the look of ambient occlusion. If set to false, the color spread is less prominent, but the look of ambient occlusion does not change with the "quality" parameter."
https://docs.chaos.com/display/CRMAX/Corona+AO+Map

"Modified how color spread is computed in CoronaAO map to avoid different results when changing sample count. Sample count was also renamed (and remapped) to Quality"
https://blog.corona-renderer.com/chaos-corona-10-released

"Modified how color spread is computed in CoronaAO map to avoid different results when changing sample count. Sample count was also renamed (and remapped) to quality."
https://forum.corona-renderer.com/index.php?topic=38385.msg211526#msg211526