View Full Version : Match-moving motionblur

04-27-2008, 02:13 AM
I used a Sony EX1 with 180 deg shutter to capture some camera movement in 3D.
A shutter setting like this will result in some motionblur.
When match-moving with SynthEyes I put a few manual trackers before the automatic process is started guiding the automatic process. When motionblur is visible I put the trackers in the middle of the blur.

When rendering a test object in LW8.5 with normal motionblur with 50% shutter applied the test object seems to shift a little up/down/left/right during playback at frames with motionblur. LW8.5 calculates the motionblur between the current and previous keyframe.

When rendering a test object without rendering motionblur the test object is locked - just like the preview in SynthEyes. This proves to me that the scene has been solved correctly and the problem must be related to the way LW handles motionblur.

Is there a way to render the motionblur before AND after the current keyframe?
Putting the SynthEyes trackers at the end of a motionblur would make it very difficult to solve such a scene accurately. So that is not a real option.

jin choung
04-27-2008, 03:25 PM

good question and interesting info.

i have no idea except for maybe trying a post render motion blur (real smart) using vectors and seeing if that works...?

good luck and i hope you get an answer.


04-28-2008, 06:10 AM
Or try to put your trackers at the head of the motion blur? To match what LW does, I think you'd have to consider motion blur to work that way.

04-29-2008, 05:18 AM
Edit: Never mind I answered my own question.

04-29-2008, 08:03 AM
Consider motion blur is the result of slow shutter speed, but also slower film speed or low lighting. So we need to consider these aspects to match it as well.

In previous LW versions, Mblur is calculated between the current and previous keyframe as you've said, what has more sense than the current implementation which is the contrary (Mblur is calculated between the current and next keyframe), since Mblur is a sample/record/registration of what has happened, not what will happen. We should have the option to choose between backward and forward motion blur (and export both motion vectors). We can reverse mBlur by setting negative values in MBlur, but this doesn't provide exactly same results for legacy scenes (what screws up some spinning light rigs).

Anyway, in this case this may happened because you have set trackers by hand in the midle of the blur zone (not in one of the extremes). In a case like that, you gonna need forward&backward mBlur, at the same time. If you don't want to track this again (as Nangleator has suggested), an option is to go with Jin Choung's suggestion. Other is to render twice (negative/positive mBlur). Another way (LW.9x only) could be to mddscan the motion and add a DP's MDDPointer in the ItemMotion Node Editor and a slight shift/offset to the motion (with an 'add' node) so that it can match with your real footage.


05-01-2008, 02:13 AM
Tracking the start or the end of a motionblur accurately is almost impossible because the tracked point fades out.

Also the length of the blur depends on the motion strength - this would change the shape of the tracked points and you lose the tracker.

I agree that LW should have an offset for the motionblur: before - at - after current keyframe.

I'm afraid waiting for a solution in LW10 is the only thing we can do.

In the meantime I set the shutter to 1/100 s (90 deg at 25fps) or faster.
It's a pitty we can't use Lightwave motionblur for better integration of CGI with video.

05-01-2008, 11:54 PM
That sounds like if solution was in blur length or shutter efficiency in your case.


12-17-2009, 04:47 PM
The problem is that LW's motion blur lacks a proper phase control. Ideally we could have our motion blur centered around a keyframe like it is in tracked footage, half the blur behind our frame, and half in front.

The workaround is to enable fractional keyframes (yikes! I hate that!) Then go to the graph editor (the old "Shift Keyframes" rounded off decimals in my tests) and select all the keys for your camera. Shift them 0.25 frames forward in time. Then render with your 50% motion blur. Note you really want to shift them by half the motion blur amount. So at 75% blur it would be 0.75 * 0.5 = 0.375

After you do this you can turn fractional keyframes back off (lock your camera). Now, magically, your scene should track correctly again.

NOTE: This will mess up the display in the OpenGL views (without motion blur). You can duplicate your original camera before the adjustment and use it to work with, switching to the corrected camera when you want to render.

What a PITA! Newtek, how about a phase control for MBlur? (Of course a phase control would change the phase for object motion as well, which is not always what you want, since it can make objects blur the frame before they move, or the frame after the come to rest.)

12-18-2009, 04:59 PM
Ironically, LW's motion blur was reversed to match other renderer's blur... renderers that also offer shutter open/close and center-on-frame options for motion blur...

12-21-2009, 08:54 AM
I'm afraid waiting for a solution in LW10 is the only thing we can do.

Reelsmart motion blur is definitely worth a shot, even without exporting vectors it works very well on rendered shots...I seem to recall that it can also remove motion blur from shots but not 100% sure.

12-21-2009, 12:39 PM
pftrack can analyze and output 2d vector motion. if you need extreme control in post..

12-22-2009, 02:48 PM
Reelsmart motion blur is definitely worth a shot, even without exporting vectors it works very well on rendered shots...I seem to recall that it can also remove motion blur from shots but not 100% sure.

For sure on that one - we got it recently and it's a real bonus. Download the trial and try it, if you can.


12-28-2009, 12:22 PM
RealSmart works well, and using motion vectors our of LW with RealSmart's Vector Blur works well as well. However, the method I describe above works perfectly.