Noise in very simple corona material!

[mga1981]

Hello friends, I have a problem with too much (I think) noise in this otherwise very simple material. Illumination is made of Corona white environment and Corona sun. Arc plane is used for background image. I used a very low resolution (800 * 600) for examples only. I have planes (portals) on each window.  How do you think, where is the problem in my scene?
Here is everything that i think you need to see about these material:

[PROH]

Why don't you use Corona Sky in environment slot?

[mga1981]

Because it makes allot more blueish tint to my scene. Is there any difference except tinting if i use corona sky?

[maru]

How does the background material look (light mtl settings?). Did you follow this guide?
https://coronarenderer.freshdesk.com/support/solutions/articles/5000515605

Be careful with blend materials+bump maps+uhd cache. They may cause troubles.

I think the portals could be places more efficiently (red lines):
(remove the old one "inside" of the balcony)

[mga1981]

I followed exactly the same guide for background image, material setup is in the picture with other materials. I'll try to repositioning my portals to your suggestions. I already tried to assign non blend material, simple Corona material with 100% reflection and 0.9 reflection glossy, no bump. The result is the same. Are you suggest to try not using uhd cache?

[Juraj]

Because it makes allot more blueish tint to my scene.

You can put CoronaSky into ColorCorrection node and desaturate it. The natural tone works well with full intensity of Sky since it counter balance naturally warm Sun.

(Alternatively, you can use CoronaSun color temperature, but imho it works stupidly, because instead of coloring Sun in changes both Sky+Sun to identical temperature, that's just weird...why would anyone want fully flat single color light for both direct+indirect)

[mga1981]

Because it makes allot more blueish tint to my scene.

You can put CoronaSky into ColorCorrection node and desaturate it. The natural tone works well with full intensity of Sky since it counter balance naturally warm Sun.

(Alternatively, you can use CoronaSun color temperature, but imho it works stupidly, because instead of coloring Sun in changes both Sky+Sun to identical temperature, that's just weird...why would anyone want fully flat single color light for both direct+indirect)

Thanks man, I'll try this approach. I think indirect lighting causing the problem with noise in my scene. What else I can do?

[Juraj]

How is your glass (windows) material setup ?

And curtains ?

[PROH]

The albedo on the brick wall seems a bit to high - try to lower it slightly and see if it helps.

Another thing I noticed, is that the bitmap in your backplate material is set to "Screen". This means that it'll show just like if had put it in the "Direct visibility override" slot. So why use a backplate? Does it emit light? Seems like you haven't used a Rayswitch for the backplate, so does the backplate affect global illumination and/or prevent/reduce the amount of light coming in?

[mga1981]

Guys i think i've found my problem, maybe the curtains make all my trouble, i tested with only Sun+Sky with desaturated color map for the sky. No geometry on windows, only portals, and seems curtains is causing the problem, i'll post material for them to give me some advice how to make them right. My glass is double sided so i don't need thin(refraction) checked.

[pokoy]

First make sure you stay away from jpegs. They might have compression artifacts, this may affect transparency sampling. Not sure but who knows.

I'd also set both reflection and refraction level to 0, it seems you don't need them as they're black anyways?

[Juraj]

Is your opacity map for curtain set to "None" in filtering ? It should. Also you can give it some translucency, every fabric is translucent to some degree, you'll get more light through.

No need to stay away from jpegs, unless you heavily compress the quality (3-4), even then the "compression artifacts" are purely visual, in B&W none. There is thread here I think by Headoff comparing different formats for alpha mapping but the conclusion
doesn't warrant any drastic difference to them. I use jpegs for everything without single issue.