Funky shadows

[tfinlay]

First, I apologize for not showing the entire image, but this is proprietary and I can't share it.

This is a cropped image of a final rendering.  The moulding you see here is the default Nickel Satin finish in Keyshot.  Wherever I have this material in my model producing some shadows below it, I often get some funky looking shadows like you see off to the right.

I have attached screenshots of my render settings also.  Can anyone tell me what might be the problem/where to look?

[DriesV]

Firstly, why have you unchecked "sharp shadows" in advanced settings? By default it should be on. I typically get better (more accurate) results with this option turned on.

Secondly, why is your overall sampling at such a high value (128)? Very rarely a material needs such high sampling. I never have felt the need to go over 64.

Thirdly, have you tried increasing the global illumination (GI) quality? By the looks of your posted image, your problem seems to be related to GI splotches. Raising this value from default 1 to 2 or 3 can help when you get splotchiness in your image. Be warned that render time increases accordingly. A value of 4 would seem ridiculous overkill in most cases to me. 

I personally would try this:

• lower sampling to 64 max.
• enable sharp shadows
• raise global illumination quality to 2

Maybe try the latter if the first two suggestions don't help much.

Final suggestion:
I have run into GI issues before with the "advanced control" rendering mode. Going with "max. time" or "max. samples" has been the solution in 99% of times. Those modes seem to handle final rendering differently. Depending on the scene it might take longer to get rid of image grain, though.

greetings,
Dries

[DriesV]

A little test with a 'problematic' scene of my own.

These are three images rendered with exact same settings, but with varrying GI levels (1-3-5).
You'll notice diminishing light/dark splotches around the OPEN/CLOSE markings.

greetings,
Dries

[tfinlay]

1)  I don't know why its unchecked... probably got turned off when I was playing with settings.  I'm extremely inexperienced with rendering, so I was just trying different things.  (As a side note - the sound is out of sync with the video on many of the Keyshot tutorials, so I gave up watching them)

2)  I thought higher sampling was better?

3)  No, I didn't realize the slider indicated the Quality of Global Illumination... I thought it was the level (the name is misleading)

I do not have the option to do max. time (network rendering).  I made the changes you said and tried it.  Definitely improved the look.  I also tried max. samples.  See images below:

EDIT:  First image might be 64 samples.  I forgot.  Oops.

[DriesV]

...
2)  I thought higher sampling was better?
...

Higher samples give you a smoother surface. That's all.
Sometimes you want just that, but at other times you might want a 'rough' look instead. In those occastions a lower sampling value of f.i. 8 introduces "sampling imperfections' that might give you just that sandy look. It's an efficient way to create 'unsmooth' surfaces.

A lot of times a very high level of sampling doesn't make much sense. High sampling doesn't make a whole lot of difference on highly reflective surfaces f.i. As a rule of thumb: higher roughness >>> higher influence of sampling on appearance (smoothness of surface).
This point is also proven by your images. I don't see much difference -concerning material appearance- between the 128 samples image and the 'improved' 32 samples image. In fact your 32 samples image looks better because of improved GI. 

Dries

[tfinlay]

Cool.  I appreciate the help!