How to deal with motion blur when rotoscoping?

[Eugene Lehnert]

How do you deal with motion blur when rotoscoping an object in a scene? For instance if I am replacing a tablet screen where a hand is passing over the screen what is your technique to add the motion blur back?

I have been rotoscoping where there is a solid image of the hand and no motion blur. Then I am trying to add it back with the furnace plugin to detect motion and add the blur. I am using an outline matte to comp the blur back over the edges of the image. I am having problems at the edge of the screen though. The motion blur is longer in the original image than in my comp. I am pushing the motion blur on the furnace plugin to make them match.

Is there a better way to do this?

Thanks

[Anonymous]

Why don’t you use the motionblur parameters in the Shape tab of the Roto node?

[Merrill DataSiteF]

When I use the motion blur parameters in the roto node I get unwanted background images. I could cut more into the foreground image but then I lose more of the subject.

[Merrill DataSiteF]

Maybe this will help explain my problem. I am compositing a new image onto the tablet so I am compositing the hand back over the image. But when I cut into the hand too much it doesn’t match the original motion blur.

[IMG]http://bohemiafilms.com/rotoscope.tiff[/IMG]

So after that I am using the F_MotionBlur node to reintroduce motion blur around the edges of the hand. I’m just wondering if there is a better way to do this?

[Merrill DataSiteF]

[IMG]http://bohemiafilms.com/rotoscope.tiff[/IMG]

[Merrill DataSiteF]

http://bohemiafilms.com/rotoscope.tiff

[Anonymous]

Ah, now I see what you mean.
I would do the following:
1. Create a mask with a natural-looking motionblur, regardless of the background objects mixing with the hand.
2. Shrink a copy of the mask to the point, where all the semi-transparent (blurred) edges are cut away. You can adjust the black point of the mask for it, the mask thus becomes hard-edged.
3. Multiply the hand with the shrunk copy of the mask.
4. Blur the multiplied result as much as to cover all the motion-blurred area of the original footage (you can adjust it more precisely later, looking at the final result)
5. Unpremult the blurred hand. You can see, that the skin color is now expanded.
6. Merge the unpremulted result over the screen image, using the original motionblurred mask.
7. Use the shrunk hand mask to put the screen image with the blurred hand over the source.

[Anonymous]

You might find my top 10 roto tips helpful: http://conradolson.com/my-top-10-roto-tips

[Anonymous]

try the rotoshapes motion blur, then if u have some unwanted background on the edges, maybe try working with the roto’s feather alittle.. to get rid of the background unwanted edges.

[Author]

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