Artefacts In Rotoshape Soft Edges

[user_deleted]

Hi there,

creating soft (feathered) edges on mildly complex rotoshapes (e.g. for moving human limbs) I get annoying artefacts within the soft edges: irregular blotches spoiling the smooth gradient. Tweaking the curves doesn't really solve the problem and would be much too tedious anyway.
Surprisingly, this "effect" is even stronger in Shake 4 than in Shake 3.

Unfortunately, the rotoshape motion blur parameter is no ideal substitute for soft-edged rotoshapes because of its lack of precision.

Anybody else experienced this problem? Any ideas for a solution?

Thanks

John

[user_deleted]

throw a median node after the rotoshape, default settings.

[user_deleted]

Thank you, mikemarcus.

The median node delivers the right effect, but unfortunately, the artefacts are too bad to be completely smoothed out by it. A combination of the median node and tweaking the rotoshape's soft edge curve might work, but the tweaking is a real pain again (as mentioned in the initial post).

I found a post in another forum mentioning that "[...] the edge feather can give funky results". So the whole problem looks like a bug in Shake.

Still, any further solutions are welcome. Thanks!

Cheers

John

[user_deleted]

I am not sure that it is a bug as much as a function (limitation) of the edge feathering algorithm. I usually achieve acceptable results with a combination of median and a slight blur. Check out the foundrys tinder plugins for a better median filter.

With experience you will learn how far you can push the splines without the matte breaking apart.

[user_deleted]

I dont have a real solution for you except that I personally try to avoid the soft edge function
whenever I can. I like to use Percentblur x,y .5 to 1 instead or add this node to the already mentioned
Median, Percentblur if necessary Lookup and Blur again and one more Expand .... a headache

[user_deleted]

Not an ideal solution, but there's something that works pretty well when there's too much banding or even artifacts on the softedge, which is adding more points inbetween.

That could be a pain if you need to animate all points, so just work on your roto as is, and add those points when you're done to get a smoother result.

As I said, not an elegant approach, but it works.

Hope that helps

[user_deleted]

Thank you all for your help!

@mikemarcus: I guess you are right that the edge feather artefacts are more of a feature limitation than a bug. However, this lets Shake appear a bit weak, when a clean gradient between curves can be made in Illustrator or Freehand since very early versions. I'll write Apple a feature/bugfix request ... maybe it'll help. At any rate, tweaking with the median and blur filters does help.

@grasshoppa: To avoid the soft edge is what a compositor friend of mine told me, too. Your alternative solution looks a bit complicated but - I think - illustrates the best thing to do: try various ways of tweaking blur and similar filters.

@bluepixel: Actually, in my case the artefacts especially occur on rotoshapes with a lot of control points. The more points the stronger the artefacts, particularly when the edge points are not drawn away from the main points and curve in a perpendicular direction (which gets sort of nasty in the "corners" of a rotoshape).

Apart from using various blur filters the motion blur parameter in the rotoshape node might not be such a bad option after all. Tweaking the shutter subparameters could match the blurred shape to the plate. I'll give that a try as well.

Again, thanks for your kind and helpful replies.

Cheers

John

[user_deleted]

If you are trying to roto motion blur, what many compositors do is to roto a hard edge and recreate the motion blur once the plate is premultiplied by the matte. That way, you dont bring through any unwanted background.

I tend to use edge feathering for mattes for colour correction etc where I can blur them quite a bit anyway.

[user_deleted]

I don't know why this works and it may be illegal, but normally you turn the motion blur on in the rotoshape by entering 1. Entering a higher number like 2 or 3 seems to smooth out the artifacts. I'm not talking about the shutter.

[user_deleted]

Hey, I was just about to post on this.

Rotoscoping a person with soft edges. Works great. Turn on motion blur and POW, it goes whacky!

It looks like the soft edge works from point 1 of the mask, to 2, to 3, then somewhere along the line it decides to not go to the next point in the mask, but back to point 1! (Or perhaps 2 or something.) You literally see a spike in the alpha channel that shoots from one point back across open space. And the soft edge stops at that point -- it's hard-edged the rest of the way around the mask.

Totally psychotic. I guess I just won't use motion blur, but for some subjects I'd think it's pretty much necessary. (Or I guess manually doing the motion blur with the soft edge is possible.)