Bizarre grain

Become a member of the CGSociety

Connect, Share, and Learn with our Large Growing CG Art Community. It's Free!

THREAD CLOSED
 
Thread Tools Search this Thread Display Modes
  06 June 2013
Bizarre grain

Working on a shot and using Phys to render. Lighting and reflections are HDR and using Indirect Illumination instead of GI. Getting an odd thing where the entire object is using the same reflective metal but parts of it have 0 grain while other parts have a ridiculous amount of grain. Easily fixed in post but I'd like to know why this is even happening. Even bumped up the blur samples since the reflective metal has blurring. Rounded edges of the gears close to the camera has 0 grain while the engine block and flat front faces of the gears have crazy grain. Any insight is greatly appreciated.

EDIT: Had to pull the video down guys, sorry. The boss doesn't trust you guys as much as I do .
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own

Last edited by Troyan : 06 June 2013 at 08:38 PM. Reason: Proprietary hardware, client asked not for public
 
  06 June 2013
Are you using an HDR with smaller bery bright spots in it? If so lowering the HDR Threshold in Physical Render settings can help. Alternatively you can also clamp the HDR itself.

Either way these super bright HDR spots can introduce a lot of grain.
__________________
http://www.bobtronic.com
 
  06 June 2013
There are some bright spots, but why is the grain only on the engine and the flat parts of the gears and not over all of the metal parts?
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own
 
  06 June 2013
Hi,

Your statement 'Lighting and reflections are HDR and using Indirect Illumination instead of GI' is a bit confusing, as Indirect Illumination is just another term for Global Illumination, or more specifically the natural effect the various GI methods are trying to simulate.

So I am not sure if there is a basic misunderstanding, but apart from that your example does not look very uncommon. The grain happens in the expected areas and is caused by the unified subsampling routine of the physical renderer. That effect also happens for the other renderers. The Anti-Aliasing/Sub-Sampling is getting more difficult as more effects are being layered on top of each other. DOF, Area Shadows, Blurry Reflections/Refractions and AA are all sampling based and demand exponential computing times if layered on top of each other.

You can observe that effect by rendering a reflective sphere with blurry reflections and very 'noisy' bumpmap. Even when you set the bump strength to a value so that it has no or almost no visual contribution to the image, the result will be more grainy than without any bump mapping.

To counter that effect you have either to turn down the number of layered effects or drastically increase the Anti-Aliasing. Also turning down the the number of samples for each effect (except from AA) can help. For the Physical Renderer you should increase the Sampling Subdivisions as far as you can afford while lowering the shadow, blurriness and sss subdivs as low as possible (You could of course increase both, but then the render times will explode).
__________________
There are holes in the sky. Where the rain gets in.
But they're ever so small. That's why the rain is thin.
 
  06 June 2013
Instead of using the GI setting in the render settings and messing with QMC and all that crap along with the Phys Renderer, I'm using the Indirect Illumination setting inside of the Phys Renderer as that tends to create less problems (or no problems, really) with flickering than using the old GI. As far as I'm concerned, they are not the same.

Yes, increasing the sampling would fix this. What AA are you talking about in the Phys renderer? The SSS is at 0. I'd just like to know why there would there be intense grain on some parts and 0 grain on others? Makes no sense.
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own
 
  06 June 2013
It's just confusion over terminology; the old GI effect and physical render's indirect illumination are both forms of global illumination.
 
  06 June 2013
Are you using the default "low" sampling quality?

Looks like grain increases on objects in distance that are most affected by DOF.
 
  06 June 2013
Originally Posted by JoelOtron: Are you using the default "low" sampling quality?

Looks like grain increases on objects in distance that are most affected by DOF.


No, that's medium but even at high there's an unexpected amount of grain. But what I'm trying to get to is why is there no grain at all on the curved surfaces but crazy grain on the flat surfaces near the camera and all over the engine block in the distance? Shouldn't there be grain everywhere?
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own
 
  06 June 2013
I think littledevil is correct in saying that a lot of it has to do with insufficient samples for the DOF effect. I'd try eliminating the DOF and see if that improves things.
 
  06 June 2013
it is hard ot be sure, my guess is also DOf as the front objects do seem to have more as well, not as severe but more noise all the same.

Best is to first turn off effects like motion blur, dof and blurry reflections, and then turn then on one by one and see when it gets introduceed.
__________________
Quote: "Until you do what you believe in, how do you know whether you believe in it or not?" -Leo Tolstoy
Kai Pedersen
 
  06 June 2013
I'm going with the DOF on this one as well.

You likely do not have the sampling subdivisions set high enough. (initial scene sampling)
This one has the most effect on DOF and MB effects.
Also, I would avoid the indirect illumination check box in the physical settings.
It is the same as QMC but has less control over the sampling.
__________________
The views expressed in this post are by no means the opinion of those making the post or of any one person in particular.
 
  06 June 2013
Here it is with no DOF. Same issue. Setting the blurry reflection samples higher does help reduce the grain, but again, why would there be absolutely no grain at all on some parts and silly amount of grain on others? Same texture, reflecting the same environment, same everything. Shouldn't there be uniform grain across everything, especially surfaces that are right next to each other?

EDIT: had to pull this also :P
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own

Last edited by Troyan : 06 June 2013 at 08:39 PM.
 
  06 June 2013
what are you using for environment (images)? All the smooth reflections you have pointed out are curved and perpendicular to the axis of the machine (and at a high angle to the camera). All the grainy areas are closer to pointing at the camera and all are smoother on the bottom than on the top - it looks like you have an image with those qualities being reflected or it's something to do with fresnel
 
  06 June 2013
noticed the same thing BDjones, the flat front facing surfaces are what is more grainy. Personally my guess is actually the direct illumination. There's obviously a fresnel, so perpendicular faces are more reflective and thus may reduce or cancel out the sample from indirect illumination for simply reflective samples. But for front facing surfaces where there is less reflection, more diffuse contribution is seen and that is being illuminated by indirect illumination and clearly doesn't have enough samples.
__________________
Quote: "Until you do what you believe in, how do you know whether you believe in it or not?" -Leo Tolstoy
Kai Pedersen
 
  06 June 2013
There is no fresnel. The scene setup is actually quite simple. I can't post the actual map since it's a purchased map (and it's huge) but I'll post a low res or screenshot tomorrow. There isn't any grain in it. The metal texture simply has reflection with some blurring and specularity set to metal. That's it. I tried it with another reflectivity HDR and although there is less grain, there's still a considerable amount of grain in the flat surfaces and none in the curved. I'll try rendering a reflective sphere and cube in that scene also tomorrow. Phys settings are the preset Medium, although turning it on High helps but it's not nearly as clean as I'd expect.

Thanks for the insights!
__________________
2014 Reel
Company website
Behance Portfolio
HyperactiveVR
I reject your reality and substitute my own
 
Thread Closed share thread



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
CGSociety
Society of Digital Artists
www.cgsociety.org

Powered by vBulletin
Copyright 2000 - 2006,
Jelsoft Enterprises Ltd.
Minimize Ads
Forum Jump
Miscellaneous

All times are GMT. The time now is 09:41 PM.


Powered by vBulletin
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.