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Anti-aliasing issue -- 3D moBlur

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pyro
Anti-aliasing issue -- 3D moBlur
by
on Nov 4, 2005 at 10:58:24 pm

Hello Maya Cows. Been awhile!

I have a new problem I was hoping to get some help with.

I'm rendering a Text object made from Bevel plus where switching 3d mo blur on causes a dramatic quality change in all AAliasing. Even when the object is only slightly moving...

The problem I am having is that when I render it without 3D MoBlur, the AA looks very nice. However, when I switch the 3D mo blur on, my edges get blocky and somewhat aliased. I've been tinkering with the settings (Maya Software) related to 3D moblur AA and cannot get a good result. In this project, I don't really need to use the 3D moBlur, but I have notice other times when the 3D mo Blur produces unusable results (such as high speed rotations with file textures, etc.)

I was hoping you might have a suggestion to improve the edge AA while 3d mo blur is switched on. Or perhaps, a tutorial with more cogent and in-depth expanations of the settings so I may understand precisely what the settings mean.

Thanks for the replies!


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Sean Fennell
Re: Anti-aliasing issue -- 3D moBlur
on Nov 4, 2005 at 11:18:59 pm

I have some tips that I've used in the past. I should warn you though these settings drastically increase render time...

First thing to know is that the min AA shading value gets overloaded when using 3d motion blur. That is to say not only does it control shading anti-aliasing, but it also controls temporal anti-aliasing which is why its set to 3 in the 3D Motion Blur Production preset. Leave it at 3 and don't turn it lower or it will create terrible aliasing artifacts in the alpha channel.

First thing you should do is increase the Max Shading Samples value to about 12 to start. That will give the AA enough sampling ceiling to give decent smoothness to the motion blur. Increase this value at increments of 1 until you get smooth enough motion blur (its best to judge the alpha channel for motion blur smoothness).

Finally what also greatly helps the smoothness and detail of the 3d motion blur are the 3d Blur Vis and Max 3d Blur Vis attributes. I usually start at 2 for 3d Blur Vis and 4 for Max 3d Blur vis. I rarely have to go above 2 for 3d Blur Vis, and often increase the Max value. These attributes help areas where motion blur is across, over, or behind semi-transparent geometry or when a motion blurred object passes in front of a non-motion blurred object. These attributes help keep a smooth transition in the sampling across those details.

I found that for very high motion blur with a lot of smear these settings help a bit, although may be slightly overkill:

Start by setting the Quality Preset to 3D Motion Blur Production and adjust the following attributes:
Shading: 3
Max Shading: 16
3D Blur Visib.: 2
Max 3D Blur Visib.: 6

If necessary you can lower the Contrast Threshold values to push the AA sampling into the higher Max Shading sample values. Do not increase Shading above 3 unless absolutely necessary, because this is the minimum number of samples allowed to take over all pixels, the higher this number goes the more samples happen ALL the time, even over black or non-contrasty pixels.

Also to give a bit of personal artistic opinion. Too much motion blur, meaning very streaky motion blur because the shutter is open very far or the Blur by Frame is large, starts to look unrealistic and overdone and also takes a LOT longer to render. A little motion blur can go a long way when viewed in motion. Its a perceptual thing, you aren't supposed to SEE it, you're just supposed to feel like it's not missing.


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pyro
Re: Anti-aliasing issue -- 3D moBlur
by
on Nov 7, 2005 at 4:16:22 pm

Thanks for the reply Sean.

I tried your settings and still, the thing was producing aliased edges. When the geometry goes quickly, the blurring looks nice, but when the object is slow or still, the aliasing returns.

In the end, I switched to Mental Ray which gave better AA results. The scene is very simple and the MR did not increase render time noticably. A colleage and I spent an hour trying to resolve this AA issue and made almost no headway until switching to MR.

Any other ideas? Like I mentioned, the issue is more when the text in this case is barely moving. The edges get blocky as though an ovesampling is adding instead of screening the overlays.





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Sean Fennell
Re: Anti-aliasing issue -- 3D moBlur
on Nov 7, 2005 at 4:48:52 pm

I just realized you never posted the settings you used initially. Can you post those settings and I can try trouble shooting it on my end. I don't ever rememeber having problems like this with motion blur. Be sure to post all the aa settings, including edge AA.


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Sean Fennell
Re: Anti-aliasing issue -- 3D moBlur
on Nov 7, 2005 at 4:49:22 pm

oh, and what version of maya you're using. never know, could be a bug.


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Pyro
Re: Anti-aliasing issue -- 3D moBlur
by
on Nov 7, 2005 at 11:08:58 pm

Thanks again, Sean. I appreciate your patience and willingness to take a stab at this!

I do not want to use filtering for these since at standard Resolution, the softening is too much even at low values. The sampled areas are not much more than 70 pixels high and the object at this frame is only moving very slowly. The artifacting is especially noticable as the object slowly moves causing very blocky edges. I'm guessing the oversampling is adding gain to the slowmoving edges. Maya 7.0

This image has nearly perfect SD anti-aliasing. Done with default "Intermediate" preset with NO 3D motion Blur.
Image hosted by Photobucket.com

This is default AA settings with 3D MoBlur. Now the problems occur. The artifacting is unusable.
Image hosted by Photobucket.com

This is your suggested AA settings (minus filtering)
Image hosted by Photobucket.com

This is a Mental Ray redered with MoBlur.
Image hosted by Photobucket.com


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Sean Fennell
Re: Anti-aliasing issue -- 3D moBlur
on Nov 7, 2005 at 11:45:44 pm

looks like you found a solution. I was unable to reliably reproduce this problem over and over. What I noticed though is that setting Shading Samples to 4 instead of 3 aleviated a lot of issues with the undersampling of motion blurred objects. I believe it comes from the temporal sampling which is jittering from frame to frame so setting shading samples to 4 adds more temporal sampling to the motion blur. First time I've ever seen this happen before so harshly though.

You should also take note to how radically different the mental ray settings are from maya's settings. In maya you get two controls for motion blur, the coverage control which is like the threshold for motion blur sample anti-aliasing and the Shading Samples. In mental ray you get over 6. Temporal sampling is a far more refined control for motion blur motion samples, separate from shading samples. In maya coverage is this temporal threshold value, and the shading samples are bundled together with motion samples. I guess it was supposed to be simpler that way, but it can cause artifacts, so lowering coverage and raising shading samples should aleviate the problem.



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