Looking for some Karma tips

Forums Houdini Lounge Looking for some Karma tips

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BrianHanke: Member; 433 posts; Joined: April 2018; Offline

Oct. 27, 2020 3:25 p.m.

I've been playing with the new 18.5 Karma and am liking a lot of the new features. Seems much more robust than the 18.0 version.

But…

I feel like I'm still missing how to use it properly. There isn't much in the way of documentation or advanced tutorials and a lot of the Karma tooltips are ??? placeholders. I'm attaching 3 renders from my Houly Speed entry. Mantra came in the fastest by far (never thought I'd say those words!) and the image is very clean. Karma with pathtracing was twice a slow, including tons of noise and some truly dreadful artifacts in the motion blur. I bumped Karma up to 256 samples and variance convergence mode for ultimate quality, leading to the third image at a whopping 17m12s. And it's still noisy compared to Mantra.

In short, I can't shake the thought that I'm really doing something wrong. Any advice from Karma experts would be appreciated! HIP file attached too just in case.

Edited by BrianHanke - Oct. 27, 2020 15:27:03

Attachments:
mantra.png (400.2 KB)
karma01.png (776.2 KB)
karma02.png (716.7 KB)
07 Speed Karma.hiplc (1.4 MB)

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dlee: Staff; 418 posts; Joined: Sept. 2016; Offline

Oct. 27, 2020 4:52 p.m.

Hi. Yes, the reason why mantra render is so fast is because there's no light in the scene, so everything is lit via unshadowed headlight. Karma is automatically creating geometry lights based on material emission on “arches” and “light” geometry, so the lighting is far, far more complex. Additionally karma render has diffuse indirect bounce enabled by default and mantra has it disabled by default. To avoid artifacts around the arches due to motion blur, I'd recommend increasing the minimum sample count on variance pixel oracle (2 isn't enough in this case and causing some buckets to terminate prematurely).

Edited by dlee - Oct. 27, 2020 17:21:10


jsmack: Member; 7747 posts; Joined: Sept. 2011; Offline

Oct. 27, 2020 5:05 p.m.

Your karma comparison isn't fair. In the mantra render, the geometry lights have no effect on the diffuse lighting in the scene, which makes for a very fast render. The headlight is the only light in the scene.

When the scenes are more or less identical, the results are closer.

Mantra 0:55s (4x4 12 max ray samples)

Karma 1:11s (16 samples, uniform sample oracle; variance convergence mode 12 max ray)

Edit:
making the karma scene more like the mantra one, the samples can be increased to get a less noisy result in a similar time.
Karma 0:51s (64 samples, variance oracle 8min; pathtraced)

Edited by jsmack - Oct. 27, 2020 17:19:56

Attachments:
tunnel_mantra_0_55.jpg (425.1 KB)
tunnel_karma_1_11.jpg (520.2 KB)
tunnel_karma_simple_0_51.jpg (363.4 KB)


BrianHanke: Member; 433 posts; Joined: April 2018; Offline

Oct. 27, 2020 5:37 p.m.

Thank you both! The 64 sample Karma image looks absolutely perfect.


BrianHanke: Member; 433 posts; Joined: April 2018; Offline

Oct. 27, 2020 5:57 p.m.

jsmack
making the karma scene more like the mantra one, the samples can be increased to get a less noisy result in a similar time.

Karma 0:51s (64 samples, variance oracle 8min; pathtraced

Hmm, I just tried with 64 samples, variance 8 minimum, pathtraced and this is the result. Doesn't look anything like yours. What am I missing?

Attachments:
karma03.png (883.8 KB)


jsmack: Member; 7747 posts; Joined: Sept. 2011; Offline

Oct. 27, 2020 6:08 p.m.

BrianHanke
What am I missing?

I made some modifications.

Attachments:
07 Speed Karma_mod.hiplc (1.5 MB)


BrianHanke: Member; 433 posts; Joined: April 2018; Offline

Oct. 27, 2020 6:46 p.m.

jsmack
I made some modifications.

Ah, I see, quite a few other things needed to be changed. Very educational, thank you.


jsmack: Member; 7747 posts; Joined: Sept. 2011; Offline

Oct. 27, 2020 7:40 p.m.

BrianHanke
jsmack
I made some modifications.

Ah, I see, quite a few other things needed to be changed. Very educational, thank you.

In karma emissive objects are treated like lights by default, which behaves like adding a diffuse bounce. The rendergeometrysettings disables that. The limits section of the karma lop is further reduced to zero bounces to match mantra default. Since there's no headlight in karma I had to add a light. I just used a distant light with no shadows since there's not really an equivalent to the headlight.
I also modified the materials by removing the diffuse/reflection components from the light sources. Since they are full bright, it just slows down the render to compute lighting as well.

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