Unusual "stains" on renderings

Started by Aglpr, October 01, 2020, 04:52:42 AM

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Hello everyone!

I had this problem one year ago but never found a solution, but I'm back using keyshot   ;)
I tried to find a similar problem but I didn't, so I try my luck with this topic.
For my first renderings, I didn't have any problem.
But even though I'm pretty sure I kept the same settings for the next renderings (clearly not I guess), I had this really strange treatment of light... Or at least I think it's about the light. The pictures speak for themselves!
If you have any idea what it could be, I'll be so happy to hear about it
(and forgive me about the terrible quality of my renderings)



You sure it isn't a bump map or roughness map that is out of scale?

Anindo Ghosh

Could you please check if you have Caustics enabled in the Lighting tab? If yes, try disabling it just to check if that helps.


Hello there ! Thanks for your answers

For the bump map or roughness I don't think so cause it is visible on several different materials on the model.
But maybe it is a matter of scale indeed, do you think it can be that the model is not correctly scaled (too small I don't know) for the environment, lighting etc ?

And the Caustics is already disabled !

I am quite sure it is something with light, I'll try to play with all the settings once again. But just for info I don't have the same computer anymore, and I also work on a different project right now, and it still does the same unfortunately  :-\

Anindo Ghosh

Would you be able to share a basic KSP file that you're facing the issue with?


Thanks a lot for trying to help me. I've attached my file, hope you can see what's wrong! I've got really basic knowledges so maybe it's super obvious...
I'll leave it temporarily and delete it if it's possible cause it's still my work so I prefer not to leave it unfinished on the internet :)

Anindo Ghosh

Sorry, I don't see any attachment - which could be because I'm looking in the wrong place.


I attached it again, I thought you were the one who downloaded it already sorry !

Anindo Ghosh

I've got it now. I'll have a look tomorrow, and let you know if I can make any sense of the problem. :-)


Thanks a lot for your time really appreciate :)

Anindo Ghosh

The staining seems to be some kind of reflection artifact, due to the light reflecting from the several spherical and disk-shaped objects to the glass surface and back. Letting it settle for a few hundred samples with CPU rendering improves the situation somewhat.

Also, when I switch to GPU rendering, the stains disappear entirely. However, the scene becomes dark, and the overall lighting looks different.

In short, I haven't found a solution other than switching to GPU rendering and then dealing with the light intensity change... or rendering with a couple of thousand samples.


Thanks a lot for your time !
I'll try that, that is strange though, I just know one person who also renders interior scene with keyshot and he never had this problem... And I have the same issue in a basic interior apartment scene with only one window !
Again thank you I'll use that option  :)

(if it's not too much to ask is it possible to delete the screenshot of the work ? I downloaded them to remember already  ;) )


there is no easy answer for this...
type "Blotchy" or "Blotchy surfaces" in the search window and you will find more information here in the forum than you can read today ...

mostly this is caused by using the "interior mode" and "caustics". in this case samples will be the key (we are talking about several thousands of samples!)
maybe you get away better with using the product mode, using less raybounces.

also depending on your lighting setup (emissives ? spots?) and the materials you used.
also an interior scene within a closed cube can cause issues as it may go nuts with the raybounces coming from all directions ... its probably better to leave the front wall open...

like I said, there is hardly ever an easy solution to this but sometimes it can be just switching from interior to product mode...

the person you are refering to has for sure spent some decent time in finding the right settings for interior renderings and knows which buttons to push. I do this very seldom and I always have to spent a lot of time to get the setup right and than I let it cook for a very long time...

so read through the forum and try out some of the ideas from there ...
sorry I do not have a better answer ...



No worries that helps already ! Thank you !
And thanks for the keyword, that was also my problem, I couldn't search for people with a similar issue cause I didn't know how to name this issue
And my computer would not handle thousands of samples I think  :-[
It's such a challenge to be a newbie on rendering softwares, indeed I guess the key is to experiment  ;)
Thanks !