corona sky (only) generates a lot of noise?

[snakebox]

Hi everyone,

I am just playing around, and trying to light an interior scene using only corona sky in the environment corona setting. it all works from a lighting point of view, but I find it REALLY hard to get rid of the intense amount of noise in the direct light pass.. like crazy amount of noise.

Not much seems to change between pass 100 and 250. I have tried change the light samples from 2 to 8... but so far im not sure it makes any real difference.
Does Corona sky just generate a lot of noise naturally? or does it need like 3500 passes instead? (seems wrong).

anyway I am using the new 1.1 build released yesterday or so.

I may be missing  something here but if anyone has any ideas please do tell.

Cheers!

[maru]

Hi,
https://coronarenderer.freshdesk.com/support/solutions/articles/5000501983

[snakebox]

Here is my quick test scene,



I ended up trying to use GI/AA at 64, and put light subdiv at 12 (or maybe it was 16).  In the same amount of passes as before, result is way better! but also takes quite a long time. I stopped it just before the 2h mark as you can see.

Also my machine is running at 4.6 ghz (quad core), but windows sees it as a 4.52 and corona still as a 4.0. Anyway, as you can see it's still quite noisy in the darker areas.

I was under the impression that most of the time, light portals actually generate more noise? at the benefit of pushing light in a bit..  I don't have a brightness or albedo problem, just GI noise.

[maru]

Can you show some render settings and materials? Or it would be best if you could share the scene.

[snakebox]

Can you show some render settings and materials? Or it would be best if you could share the scene.

I archived the scene (about a 100mb with maps)

https://www.dropbox.com/s/8cmrx45q99extxo/c.sky.test.zip?dl=0

oh and its saved in max2016 (forgot to save it down and my upload is slow, if its a problem let me know).

[maru]

Would be great if you could resave to max2015.

[snakebox]

Would be great if you could resave to max2015.

No problem, so I do apologies for making this a little messy.

here is the 2015 max file, https://www.dropbox.com/s/e7clje33scka45h/c.sky.test.2015.zip?dl=0

You would still need the 2016 (archive) for the textures, and I just realised that it probably will tell you 2 is missing when you open the file (just ignore them).

Thanks! 

[Dervish]

I checked your scene.

Problems I found.

1. Thick Glass, too many subdivisions, wrong material setup.
2. Some of your materials were setup incorrectly.
Go here: https://corona-renderer.com/resources/materials/ - free basic and complex material setups, learn from them.
3. You had legacy ticked in advanced material options, not sure if that can cause issues.
4. Your backplate was setup wrong. see : https://coronarenderer.freshdesk.com/support/solutions/articles/5000554427-how-to-compose-3d-objects-into-photos-backplates-and-matte-shadow-
5. I found more noise in CESSENTIAL_Indirect, I am using default render settings apart from exposure + compress.
6> Just a 6min render on my noob pc, maybe in one hour it would be clean with a few tweaks - cheats.
Raw renders.

[maru]

4. Your backplate was setup wrong. see : https://coronarenderer.freshdesk.com/support/solutions/articles/5000554427-how-to-compose-3d-objects-into-photos-backplates-and-matte-shadow-

I will check the scene in a while, but I guess this is what you meant: https://coronarenderer.freshdesk.com/support/solutions/articles/5000515605

[maru]

Ok, checked it, here are my notes, fixed scene and 2min renders:

-PORTALS! definitely required here https://coronarenderer.freshdesk.com/support/solutions/articles/5000501660

-geometry errors in the room (shell modifier - always use "straighten corners" option)

-background material was incorrect (light mtl with emit light on??), see above post, use the rayswitch one

-corona sky settings are strange, but this is the point of this topic, so no, the noise was not caused by sky :)

-reset render settings to defaults, then tweaked them a bit (more direct than GI samples)

[snakebox]

Thanks guys, will go through this.

much appreciated.

[snakebox]

Your suggestions makes a lot of sense!  So thank you all for that!

I do have one question.. it has to do with the diffuse value when setting up a simple glass shader.

The guides posted here suggest that you should put the diffuse value at 0.0 and leave colour at mid grey or what ever.

example scenes like this:
https://forum.corona-renderer.com/index.php/topic,8259.0.html

He used 1.0 and used the colour to control the diffuse tint of the glass.  I know that technically glass has no diffuse, and whether you make the value 0.0 or leave it at 1.0 and make the colour 100% black, it should give you the visual result.  How ever, is there a tech-difference in Corona between the two?

cheers

[maru]

I know that technically glass has no diffuse, and whether you make the value 0.0 or leave it at 1.0 and make the colour 100% black, it should give you the visual result.  How ever, is there a tech-difference in Corona between the two?
cheers

Diffuse color is only applied to the surface. So you may want to use it if you have for example dirty/dusty glass.
About 0*color or 1*black - there is no technical difference. It's just a color value. Color is multiplied by level, that's all. You can hover over each parameter in Max ui to see a short description.

For "tint" of the glass you should use absorption color and distance instead of diffuse color, or refraction color depending on the case.