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Flicker-free FG animation with mental ray in 3ds Max

| Your Rating:
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(Score 4.38 out of 5 after 16 Votes)
| Comments 9
Date Added: 8th March 2012
Software used:

As we can see, the current AA settings (1-16, 0.05) aren't enough to generate nice, fine details. Check on background geometry and you can see how those lanterns and hangar buildings have bad outlines. Also there isn't much detail generated on the front planes in the foreground. We need higher settings. So I would up Min-Max to 4-64 and Spatial Contrast to 0.02. Here is the result (Fig.06).


Still there are little details not generated. Check the lanterns and those buildings in the background. So let's lower the Spatial Contrast setting to 0.01 (for all RGBA) and check the result (Fig.07).


The details look good! For the final animation, I changed the FG point density to 1.0, FG points to 150 and AA settings to 4-64, with 0.012 Spatial Contrast and little bit of glow using a Glare output shader. (Note: those background lanterns have been intentionally given a higher self-illumination value to get the glow. Physically it should be lower as it fades into the distance). Let's see the result (watch in full screen with HD on)(Fig.08).


As we can see, it's flicker-free animation. So whenever it's flickering in mental ray, it's mostly due to bad sampling/AA values. (Note: we must check these using the Diagnostic tool after calculating FG maps. For some reason I find that rendering with FG is much faster than rendering without FG. So use the Diagnostic tool to fine-tune the AA after calculating the FG map).

Final Thoughts

1. Calculate the FG map first, then use diagnostic utilities to fine-tune the FG map and AA settings. Use the Compare tool or load in "Ram Player" with different AA settings and diagnostic images, and compare the differences. Use Trace Depth values according to reflection/refraction amount you need in the scene.

2. A Sampling value for AA Min-Max of 4-64 is the optimal value and will work for most types of scenes. When you need to, adjust the Spatial Contrast settings according to your needs.

3. If you are rendering with mental ray, always render in high resolution like full HD 1920 x 1080 pixels. The above tests were done with 1280 x 720 pixels size because of Vimeo 720p upload limits. I am not saying that you need to render at double or more resolution than the required size to not get that AA flickering issue, but you will always get viewable details with full resolution and 1920 x 1080 pixels size is the minimum for rendering in mental ray.

4. Also, as you increase resolution, you can use higher values with Spatial Contrast settings. In this example, if I would do rendering with the 1920 x 1080 pixels size, which will require 0.017 Spatial Contrast settings. And, of course, the rendering time was just five minutes per frame (for 1280 x 720p res) on i7 930 overclocked 4.0 Ghz.

Reference and resources: Zap Anderson ( and Jeff Patton( Thanks for providing great learning materials for mental ray.


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Readers Comments (Newest on Top)
Hanumant on Wed, 31 July 2013 7:04am
i want to know that did u use daylight system in rendering... what did u use for background sky... I m using mental ray for my walkthrougs... i use daylight system for lighting but cant use any backdrop... becauz when i use it my scene gets too dark... so plz tell me how to use effective backdrop...
Sebastienczaja on Thu, 28 February 2013 9:21am
Good Job!!Thanks!!!
Rawalanche on Wed, 14 March 2012 10:03am
That is usually due to the more contrast in the scene. FG does not anyhow directly accelerate AA, but if there is more even lighting in the scene with less contrasting difference, spatial AA, which works based on color contrast will have to do a bit less work. Especially when it comes to sampling area lights ;) So yeah, unified sampling, glossy reflections rays set at 1, area light samples at 2, Min1 - Max128 Unified sampling, and then all you have to do is keep raising quality parameter until render looks clean. Start at 1, and keep raising it. Value of 4-8 usually ends up being sufficient.
Jignesh Jariwala on Wed, 14 March 2012 6:48am
Good tips Rawalanche! Using less glossy and shadow samples and controlling everything with unified sampling sounds good! I will check that. As for FG, I noticed that when scene rendered without FG then it's much slower than rendered with FG on. (even with AO projected lighting, it's slower than FG)
Rawalanche on Mon, 12 March 2012 3:34pm
Actually, I am using FG all the time, but final gather has absolutely nothing to do with speed of quality of antialiasing. A few tips to optimally use unified sampling: Decrease glossy samples on all of your materials to 1. Set the samples of all your area lights to 2. Set Min 1, Max 128 samples, set cutoff to 0,025 and then control quality of your rendering using quality parameter. It will control quality of everything, including glossy reflections, DoF or Motion blur. When using unified sampling, glossy rays amount on the materials is actually a multiplier, not total ray count like in case of adaptive sampling. Make sure all your materials are modern mentalray materials, preferably Arch&Design. Never use legacy shaders (standard material, raytraced, dgs, etc..) Well tuned unified sampling will give you a LOT faster rendertimes than Min4 Max64 adaptive sampling, as well as more control over final quality.
Jignesh Jariwala on Sat, 10 March 2012 2:57pm
Hi Rawalanche, I have checked "unified sampling" and so far I found it really slow compare to quality of current adaptive sampling. Also if you are raising and getting high render times, it's mostly becoz you maynot be using FG. Using FG I rarely get high render times unless there are lots of raytraced or transperent objects. Anyway tutorial is about, how to find and eliminate flickering using diagnostic tools.
Jignesh Jariwala on Sat, 10 March 2012 2:51pm
Hi Rawalanche, I have checked "unified sampling" and so far I found it really slow compare to quality of current adaptive sampling. Anyway tutorial is about to how to find and eliminate flickering using diagnostic tools.
Rawalanche on Fri, 09 March 2012 9:03pm
Raising AA so high will give you unacceptably high rendertimes. A lot better way to eliminate flickering is to use new Unified Sampling introduced in Mental Ray 3.9, which will give you a lot better antialiasing detail at about the same time, and of course eliminate all the flickering. Also, it resolved rendered Depth of Field and Motion blur a lot faster with less noise ;)
Joshpurple on Thu, 08 March 2012 7:49pm
Great, Thank you :) !
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