Understanding Motion Blur

I’ve not only seen the wrapping problem, but another. With points that were moving L to R, I got a vertical motion blur. While there was a small amount of vertical movement, it was like 2 down, 10 over and the MB was just wrong. Perhaps you need to look at MB and do it based on pixel tracking of some sort because the spline based MB isn’t work. if there is a way to undo the knots, that would be great.

Steve Oakley

I like the idea of what you guys are attempting to do. If you get these artifacts worked out than I would probably use it most of the time. But I also think a option to use the old tried and true method would be great for times when the new solution doesn’t work out.

The first time I turned on motion blur I got the artifacts you are talking about above with the curves turning in on themselves. The way motor does motion blur seems to me as a solution to a problem that wasn’t there. What about just having a option to calculate motion blur based on rendering multiple sub-frames and combining them?

lets say you animate a spline in aftereffects or fusion or whatever. the program will take the previous and next frame into account and render multiple in-between shapes fading them into the current frame’s shape in order to create a smooth transition from one frame to another. This of course means you have to render 5-10x the amount of mattes per frame, but it creates a very stable motion blur that doesn’t break down when you have a complicated shape. Personally I was very surprised that the roto I made was too complex for a correct motion blur because it was actually very very simple.

—Quote (Originally by diffuse)—
What about just having a option to calculate motion blur based on rendering multiple sub-frames and combining them?
—End Quote—

Please ellaborate a liitle on this… not to sure what you mean.

—Quote (Originally by diffuse)—
The first time I turned on motion blur I got the artifacts you are talking about above with the curves turning in on themselves. The way motor does motion blur seems to me as a solution to a problem that wasn’t there.
—End Quote—

Motion blur in it’s current form was designed for a major project we took on internally and it worked wonders for the subtle blur required on most elements, saving days if not weeks of keyframing to add very realistic motion.

The current functionality is very useful in many cases, provided accurate tracking was achieved.

Nonetheless we are very open to suggestions / recommendations on improvements / additions to the feature.

Motion blur is ideal for adding subtle motion based on accurate tracking of elements, however in extreme cases the tracking causes inaccurate blur and even causes the blur edge to curve in on itself.

Having many points close together, could also cause inaccurcies.

To fix the inaccuracies, manually keyframe the blur settings for the individual points that cause problems.

Motion blur is a great time saver when on needs to add that very subtle blur / lag of a knee bouncing to the beat of music but the normal edge offsets work better on extreme blur. In most cased it should be possible to combine Motion blur with the normal edges to find a combination that works.

We recommend doing a trial or two, alternating between Track and Contour as Motion Blur Source, to gain proper understanding of how it works. (read the below excerpt from the manual)

As described in the *monet *guide (http://www.imagineersystems.com/downloads/monet/MonetGuide.pdf) :
[Layers / Motion Blur - pg 94, current version]

—Quote—
Motion Blur
These controls allow you to create motion blurred mattes. Click on Apply to switch on the feature. You can then choose the Source of Motion with which to drive the blur either from the Track (the default) or the Contour. If no layer keyframes exist on a specific layer, and Link Contours to Track is on, it makes no difference whether Track or Contour is selected as the Source of Motion. However when dealing with layer keyframes there may be an advantage to using Contour as Source of Motion as it will achieve more detail in the blur, since it computes the blur independently at each point on the contour. Please test to find which setting achieves the most desired
result.

*Please note: *when a layer is linked to tracking data by activating Link Contours to Track, and Motion Blur is applied, then the tracking data drives the motion blur regardless of which option is selected for Source of Motion. Selecting Track as Source of Motion computes motion blur for all points on the contour as opposed to computing the blur independently at each point on the contour as is the case when selecting Contour as Source of Motion.

When a layer is not linked to any tracking at all, selecting Track as Source of Motion will result in no motion blur, regardless of whether any layer keyframes exist. The value below the Apply button is used to scale the size of the blur relative to the size of the motion vectors. The default value 0.25 is equivalent to the camera integration time equaling ¼ of the frame time.
—End Quote—

—Quote (Originally by diffuse)—
…curves turning in on themselves.
—End Quote—

This seems to be a bug with the Motion Blur.
I’m attaching samples of the shot we got from Diffuse.

We are trying to track down the issue.

We realise the Motion Blur requires some work, as can be deducted from this thread.

Here is a possible work around, not sure if it will always be an option but it potential resolve the refernced sample.

OPTION 1:
Adjust the weight of the point causing the bad MBlur.
This may or may not work depending on points either side of the point in question.

*OPTION 2:
*- Add points either side of the point in question and select all three points.

  • Control the weights of all three points similtaneously to smooth out the MBlur.

*OPTION 3:
*- Similar to Option2, but minipulate edge offsets to try and smooth out MBlur.

—Quote (Originally by steve oakley)—
I’ve not only seen the wrapping problem, but another. With points that were moving L to R, I got a vertical motion blur. While there was a small amount of vertical movement, it was like 2 down, 10 over and the MB was just wrong. Perhaps you need to look at MB and do it based on pixel tracking of some sort because the spline based MB isn’t work. if there is a way to undo the knots, that would be great.

Steve Oakley
—End Quote—

Steve if you could let us have the project file you are refering to that would be great. Only the project file, I will post snapshots on this thread for further discussions and explanations.

Were you using Track on Contour as source? And was the layer tracked?

—Quote (Originally by Jay)—
OPTION 1:
Adjust the weight of the point causing the bad MBlur.
This may or may not work depending on points either side of the point in question.
—End Quote—

Option 1, snapshot

—Quote (Originally by Jay)—
*OPTION 2:
*- Add points either side of the point in question and select all three points.

  • Control the weights of all three points similtaneously to smooth out the MBlur.
    —End Quote—

Option 2 snapshot 1

—Quote (Originally by Jay)—
*OPTION 2:
*- Add points either side of the point in question and select all three points.

  • Control the weights of all three points similtaneously to smooth out the MBlur.
    —End Quote—

Option 2 snapshot 2

—Quote (Originally by Jay)—
*OPTION 3:
*- Similar to Option2, but minipulate edge offsets to try and smooth out MBlur.
—End Quote—

Option 3 snapshot

NOTE! Motor v1 NEW Motion Blur algorithm.

In short Motor v1 preview/displays motion blur via OpenGL for interactive real-time display, however the rendering now utilizes our more advance Monet motion blur. (The OpenGL preview is essential the legacy Motion Blur as per the earlier posts on this thread and subsequently pertain the issues mentioned on this thread. The new Render Motion Blur however works 100%)

In order to see the Rendered Motion blur go to View Controls (Should be Top Right depending on your GUI layout) and view the Matte for a specific layer. This view represents the actual rendered result - unfortunately only per layer.

Our goal is to GPU render the Motion Blur and drop the preview motion blur.

The idea behind the motion blur feature is that it is interactive: you can see the blurred edge as you adjust your curves. This is done by creating a third motion-blurred curve outside the main and edge curves. Currently it doesn’t work well because of the artefacts. These are caused by the difficulties in handling self-intersecting curves. We will be working on this feature and hope to have a more usable version soon. As Diffuse says one alternative is to average the mattes from nearby and in-between frames, which I think we could do fairly easily. Anyone have any comments on this?