Object Motion Blur Strangeness

I have a MAX8 scene where a camera is following a car.  I am using the
scanline renderer and I have Object Motion Blur applied to the chrome 
wheels
of the car.  On frame 1 and all subsequent frames, the chrome rims are
rendered with their appropriate blurring and they appear as dark chrome.

As the camera follows the car, the car crashes and comes to a stop and the
wheels stop rotating too.  The camera continues to move closer and then it
too comes to a stop.  The instant the camera comes to a stop, the wheel 
rims
instantly brighten to a lighter shade of chrome.

Any idea why this is happening?  The helpfile seems to imply that Object
Motion Blur has nothing to do with the camera, yet the intant the camera
stops moving, rims brighten.

As an aside, when rendering with Object Motion Blur on the rims render 
dark.
If I turn OMB off and render a frame, the rims render light.

Thanks!

Sincerely,

Mike Truly
____________________________________________
Truly Media        1.800.829.4990
email:        mike@trulymedia.com
web:    http://www.trulymedia.com

Are your MB samples the same as your MB subdivisions? Are you using multipass 
as well? Are you using an antialiaser other than Area, or material 
supersampling? What kind of material is on the wheels?

My guess is that the motion blur's material samples are being clamped before 
they're integrated, and that when neither the camera nor wheels are moving, 
object motion blur is automatically bypassed, along with whatever's 
causing the premature clamping.

Try sticking extra keys on the camera and/or wheels - even if the last 
stretch of animation is dead flat - as this will convince Max that the objects 
are still moving (albeit with zero speed) and hopefully that switch from 
moving/dim to still/bright won't show up.

Alex,

Thanks very much for the ideas!

MB samples/subdivs...the same (OMB settings at their defaults).  No
multipass.  Area anti-aliaser. No supersampling.  Material is a standard
phong with a bitmap reflection map.

The wheels are rotated using parameter-out-of-range types and a multiplier
curve.  Near the end of the animation, the multiplier goes to 0 and the
wheels stop rotating entirely but the camera continues to move for a bit
then stops.  When the camera stops, the wheel rims brighten.  I looked into
your suggestion of adding keys and the the multiplier curve for the wheels
already had an extra.  Then I tried bumping the first wheel stopping key up
to .001 rather than 0 to keep it moving.  No joy.  I added an extra key to
the camera motion.  No joy.

Unfortunately, adding another key and keeping the camera moving an
imperceptibly small distance doesn't seem to help.  The rims still brighten
when it hits the original camera stop keyframe 553 (even when the camera is
still moving to the new key on frame 600).  It takes 2:37 on frame 553 but
if I choose to render frame 552, it takes :37 seconds.  It doesn't like the
frame with the key.

Here is a link to a MAX file showing the problem.  Render frame 552 and the
rims are dark, render 553 and they brighten.

http://www.trulymedia.com/issues/object_motion_blur_brighten_problem.zip

Thanks!

Sincerely,

Mike Truly
____________________________________________
Truly Media        1.800.829.4990
email:        mike@trulymedia.com
web:    http://www.trulymedia.com