Noise from lighting doesn't go away

[KlaasK]

Hi everyone!

I'm trying to render a car in a night environment. But no matter how long I let it render, there is always some leftover noise that doesn't go away.

The bridge on which the car drives is 3d geometry. Around the geometry is a night HDRi with many lights and reflections. Also, the tail light of the car is emissive red. The wheels and bridge have motion blur. Render mode is interior mode. I have rendered on maximum time setting for 10 hours (=230 samples). After about 2 hours the image looks the same as after 10 hours.

Is it the render mode? Or do I need to wait even longer? Any tips would be welcome!

Klaas

[TGS808]

https://youtu.be/XeZSUR-_Svw

[Eugen Fetsch]

The settings in the lighting tab are the key to solve your issue. Try to increase the GI samples or shadow quality and see what happens with a region render. You can try the custom control feature too, that has a "denoising" filter built in. How to control the settings and what they do is very well described in the KS manual.

If nothing helps, try to denoise your image with external denoisers. Like...
"D-NOISE" for Blender (free). It can handle external images using the OptiX AI-denoiser from NVIDIA (Nvidia GPU required).

... or "AI Clear" ($59.99)

Or you can compile and use the "Intel Open Image Denoise" ... This one is also open source (free), works well on low samples images, but you need some programming skills and it's not as convenient as AI Clear or D-NOISE. There is a Blender branch on github that includes this denoiser (https://developer.blender.org/D4304), but again - you would need to compile on your own. 

Hope some of the information is helpful.
Cheers
Eugen

[KlaasK]

@Eugen, thanks for your comprehensive reply!

I will try tweaking the lighting settings first. I unknowingly assumed that huge render times would sort of overrule the lighting settings, but I don't know why . If that doesn't solve the problem, I will have a look at D-NOISE (and the Photoshop tricks from @TGS808's video link).

It may take a while to get new results, but I will post them here when ready!

Thanks
Klaas

[TGS808]

Sometimes those "hot pixels" or "fireflies" never go away no matter how long you render for. The tip in the video I posted works really well. In fact, perfectly I'd say. You can fix the problem in no time with very little work. The video is from Esben Oxholm who, if you're not familiar with yet from this forum, is a KeyShot master. He's without question, one of the very best. If he was unable to fix the "fireflies" with various render settings in KeyShot than nobody likely can. Definitely try his tip.

[Esben Oxholm]

If he was unable to fix the "fireflies" with various render settings in KeyShot than nobody likely can.

Thank you for the very nice words TGS808 and for sharing the tutorial. Appreciate it.

With that said I think a lot of people can fix things in KeyShot I can't. I just do whatever is fastes for my workflow.
I'm fairly proficient with Photoshop and if I know I can fix something with 5 minutes of Photoshop I usually do that instead of spending an unknown time of tweaking and rendering. Works fine for one offs, but if you have to do 50 renderings with the same problem it will suddenly be 250 minutes of Photoshop work and it might be more efficient spending a bit more time in KeyShot to optimize things. Just something worth considering.

But again, as you point out, sometimes it just seems impossible to get rid of the fireflies no matter the rendering settings and render time

Cheers,

[KlaasK]

Ok, apparently turning on caustics was a bad idea .
Going for another run, now with caustics off...

I will also try the photoshop method..

[TGS808]

Thank you for the very nice words TGS808 and for sharing the tutorial. Appreciate it.

Anytime, Esben.   I too am proficient with Photoshop and definitely subscribe to the "right tool for the job" methodology. The fix you provided in that video has never failed me. As fast as KeyShot is, using your tip is faster. And the results are flawless.