Black pixel artifacts in Karma (Random Walk SSS)

Forums Solaris and Karma Black pixel artifacts in Karma (Random Walk SSS)

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Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 24, 2020 12:14 a.m.

Hi,

I'm getting allot of black pixel artifacts in Karma renders. What is the correct way to deal with this?

Here is a test with the new Random Walk SSS shader. HDRi from HDRiHaven.

Edited by Werner Ziemerink - Feb. 26, 2020 15:00:20

Attachments:
Karma_RW_SSS.png (313.7 KB)
Karma_RW_SSS_02.png (421.2 KB)

Werner Ziemerink
Head of 3D
www.luma.co.za


jsmack: Member; 7759 posts; Joined: Sept. 2011; Offline

Feb. 24, 2020 3:44 a.m.

Either switch to uniform sampling, or set variance to 0 (for interactive renders). Variance sampling is still broken, or at least is completely unacceptable in image quality.

I somewhat disagree with the notion that pixel samples can be non-uniform, it always leads to artifacts. VRay with adaptive dmc always has weird holes in the dark areas because the adaptive sampling didn't use enough samples. Karma is even worse, where the holes are always pure black pixels on any shaded areas.


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 24, 2020 4:20 a.m.

Thanks jsmack. I will give it a go.

Werner Ziemerink
Head of 3D
www.luma.co.za


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 24, 2020 5:15 a.m.

Yep, that worked. Thanks again.

Attachments:
RW_SSS_2.gif (4.6 MB)

Werner Ziemerink
Head of 3D
www.luma.co.za


blackpixel: Member; 182 posts; Joined: April 2009; Offline

Feb. 24, 2020 6:02 a.m.

Just for the record: I wasn't involved in the creation of those artifacts!


jason_iversen: Member; 12456 posts; Joined: July 2005; Online

Feb. 25, 2020 4:01 a.m.

Looks good - is that using the new random-walk SSS?
And yes, we're looking forward (anxious) for a fix to the variance issue too.

Jason Iversen, Technology Supervisor & FX Pipeline/R+D Lead @ Weta FX
also, http://www.odforce.net [www.odforce.net]


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 25, 2020 6:12 a.m.

Yes, that is the new Random Walk.
It is a bit over saturated, because I was too lazy to convert the textures(Aces),
but it works…if Karma does not crash on me every two minutes.

Werner Ziemerink
Head of 3D
www.luma.co.za


Siavash Tehrani: Member; 710 posts; Joined: July 2005; Online

Feb. 25, 2020 9:42 a.m.

Yup, that's looking very good Werner.


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 26, 2020 12:19 a.m.

Thanks DaJuice.

Here is a quick re render with OCIO transform working in the latest build.
The random walk SSS seams to retain details much better. I am a very happy man.

Edited by Werner Ziemerink - Feb. 26, 2020 04:05:37

Attachments:
RW_SSS_4.gif (2.8 MB)

Werner Ziemerink
Head of 3D
www.luma.co.za


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 26, 2020 4:12 a.m.

This is what Multiscatter SSS looks like for comparison.

Attachments:
MultiScatter_SSS_1.gif (1.8 MB)

Werner Ziemerink
Head of 3D
www.luma.co.za


TwinSnakes007: Member; 604 posts; Joined: July 2013; Offline

Feb. 26, 2020 8:15 a.m.

What's the rendertime different between Random Walk SSS and Multi SSS?

Houdini Indie
Karma/Redshift 3D


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 26, 2020 9:21 a.m.

Daryl Dunlap
What's the rendertime different between Random Walk SSS and Multi SSS?

They are both equally slow to clean up, but Random Walk SSS does make it worth it.

I did not check render times as I fired them off before I went to bed.

Edited by Werner Ziemerink - Feb. 26, 2020 09:58:02

Werner Ziemerink
Head of 3D
www.luma.co.za


jsmack: Member; 7759 posts; Joined: Sept. 2011; Offline

Feb. 26, 2020 11:36 a.m.

With uniform sampling, I think everything takes about the same amount of time. Did you notice that the albedo of the random walk sss seemed low? It also seemed like the mfp was much lower in appearance than with the old diffusion based sss. The resulting color seemed pretty far removed from the color parameter, as well as the sss color seeming to have a very different effect than with the other models. Is this just the nature of the algorithm?

Attachments:
full_scatter.jpg (437.4 KB)
randomwalk.jpg (418.2 KB)
randomwalk_triple_mfp.jpg (392.1 KB)
diffuse.jpg (355.9 KB)


dlee: Staff; 419 posts; Joined: Sept. 2016; Offline

Feb. 26, 2020 1:51 p.m.

Do you have scale applied to the object? Currently there seems to be a bug with random walk where it can behave erratically with scaling which might account for larger differences (this will be addressed shortly).


jsmack: Member; 7759 posts; Joined: Sept. 2011; Offline

Feb. 26, 2020 4:06 p.m.

dlee
Do you have scale applied to the object? Currently there seems to be a bug with random walk where it can behave erratically with scaling which might account for larger differences (this will be addressed shortly).

I do, in fact. The shell was modeled in mm or something so I scaled it down by 0.01.


dlee: Staff; 419 posts; Joined: Sept. 2016; Offline

Feb. 26, 2020 7:36 p.m.

The fix is in the upcoming daily build. It should behave better now!


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 27, 2020 midnight

Good the hear. Thanks.

The head I rendered was scaled down 0.01 as well, but would it have made a difference if the object was scaled in Obj level instead of in Solaris?

Edited by Werner Ziemerink - Feb. 27, 2020 00:08:43

Werner Ziemerink
Head of 3D
www.luma.co.za


dlee: Staff; 419 posts; Joined: Sept. 2016; Offline

Feb. 27, 2020 10:22 a.m.

Scene Import would've preserved the transforms, so I assume your renders were affected as well.


jsmack: Member; 7759 posts; Joined: Sept. 2011; Offline

Feb. 27, 2020 12:49 p.m.

Anyone seeing crashes with husk renders containing the random walk? When I render with 256 samples, they go for several minutes and then it exits as if it's done, but no image is output. I assume it crashed because the time elapsed is too low for it to have reached 256 samples. It doesn't seem to have trouble with 16 samples, or interactively. If I render at a low enough resolution it will output, but anything such as 960x540 or above does not.

https://www.dropbox.com/s/y1xfqdef5i1pt8g/random_sss.zip?dl=0 [www.dropbox.com]


Werner Ziemerink: Member; 1265 posts; Joined: March 2014; Offline

Feb. 27, 2020 1:10 p.m.

Yes, I'm getting allot more crashes with Build 392. No image output.

Werner Ziemerink
Head of 3D
www.luma.co.za

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