moyion blur and ao

[royter]

i am rendering an animation with an motion blur and an ao pass.
will i get good results if i don't mtion blur my AO pass in my animation?

[haggi]

Well, you'll get sharp corners and edges. "Good results" depend a bit from what you expect to get and what is "good" for you.

[bart]

Just a hunch that when you turned on motion blur for your AO pass, it got incredibly long to render ...

If you use 3D motion blur, keep in mind that you don't need as many samples for your AO. That is because at any given intersection point, ie, at a spatial sample, the number of time samples are averaged together. Each time sample will intersect your object and run the AO which shoots out samples.

So with a small amount of motion, you could almost divide the original number of AO samples by the number of time samples to get the same quality. Less with larger motion, but still will give you significant time savings.

[royter]

bart you are right, motion bluring the ao pass takes crazy time to render.

i tried to turn off the motion blur for the ao pass, but when i overlay the render and the ao pass of the same frame, they don't correspond spatially, there is a little offset in the camera produced by the motion blur of the original render.

now i already started rendering the animation with the "no deformation" motion blur ( motion blur by : 1.2)
So, i guess that i have no choice but to use the motion blur for my ao pass
with the same 1.2 value.

But the problem is, even if i turn off the motion blur for all my objects, (and turning the "no deformation" motion blur ON in the render globals) it's still taking crazy time to render.

All i need for my AO pass, is to render with same offset frame of my original render but without the motion, is it possible? it would be great.

[bart]

Let me restate this ... you don't need as many samples for your AO anymore, once you turn on 3D motion blur.

How many time samples (Maya 8.5) are you using for motion?
(For previous versions, this is the inverse of the time contrast value.)

Try dividing your number of AO samples by the time samples. Then, if it isn't quite high enough quality of AO, slowly work back up until it passes. I think you will find that you end up with much less AO sampling to get the same quality.

Also, try to make quality judgements not on a single static frame, but on the shot that is in motion. In addition, ensure the judgement includes using the filtering you will eventually use, say gauss 3 3, as that is pretty common.

In my post above, I tried to describe why this technique works.

[royter]

i am using 1 contrast and time sample for my mtion blur.

i think i resolved it by turning the shutter close value of the motion blur to 0.
now, it is rendering a little faster (70 samples for ao).
i don't have motion blur in ao, but it corresponds to my originla render.

i hope it works.

[bart]

Shutter close of 0 is the same as turning off motion blur.

In custom motion blur offsets, there is a back offset value of .5 by default.
This will make key frames sit in the middle of motion blur paths.

Set to 0 if you want the beginning of a blur path to be the beginning of the frame time.

Maybe you could use this to adjust the positioning of your AO pass.

Please remind me which version of Maya you are using.

[royter]

8.5

[ChristopherP]

Just a thought...wouldn't it make more sense to be adding the motion blur in post (via ReelSmart MotionBlur or similar) in such cases!?
I've used it quite often in the past and in 99% of the scenes it works flawlessly...


Cheers
Christopher

[royter]

can you gige more ressources or tutorial links?