Grainy Edges When Keying

[user_deleted]

Hi

I have now and then the problem that when I pull a matte from a shot (for example someone with lang hair standing in front of green-screen), that the edges of my matte are to grainy. And after I render, the edge is realy jittering.
I allready tried a lot to solve my problem (blurring only blue-channel, blur-node after matte, ... --> I always loose to much detail) but I don't have any inspiration left.

If I had one, a degrain-tool would help me maybe. But is there somebody else who can give me some other tips than buy an expensive degrainer?

The images are 2k-film, but I also have it now and then with video.

I also have to say that I make a hard matte with primatte (for inside), and then a softmatte with keylight. And I don't push my keylight that hard (screenRange).

Thanks for help ...
Bert

[user_deleted]

i dont have much experience with this situation, but i'd guess that there's not much you can do except blurring or degraining (which looses detail as well). anybody had luck with the median filter?

some people here got good degraining results with the expensive plug-ins, but personally i've always ended up with an artificial look that i didnt like at all... shouldnt be an issue with a matte though.
if the objects arent moving a lot, you could also try to average frames for a smoother key.

sorry that i cant be of more help.
++ christoph ++

[user_deleted]

i have had this problem and I used the furnace degrain or denoise plugin which worked great. other than that you could try a median node or the frame averaging technique, but in my experience this isn't as good.

cheers,

kim

[user_deleted]

ok,

I seems to me that furnace really has some good tools that are not default in shake (or that you can't build with the default nodes).
I see it a lot in this forum.

i'm gonna ask my boss, hehe

thanks for help

Bert

[director]

Have you tried using the Edge Blending Technique described in Wright's Book?

[user_deleted]

sometimes i use a luma matte on one of the channels, say green if you're on green screen, just for the edges and the use a max with the keylight to add them together. oddly in the manual they use this technique for DV footage but it works pretty well on film to.

[user_deleted]

QUOTE(director @ 11/02/06, 07:51 PM) [snapback]251420[/snapback]
Have you tried using the Edge Blending Technique described in Wright's Book?

QUOTE(silk @ 11/03/06, 06:37 AM) [snapback]251462[/snapback]
sometimes i use a luma matte on one of the channels, say green if you're on green screen, just for the edges and the use a max with the keylight to add them together. oddly in the manual they use this technique for DV footage but it works pretty well on film to.

I'm gonna try them both, and then I let you know.

Bert

[director]

You should see some really good results with a Soft Comp/ Hard Comp.

Step 1. Create the "soft" matte. It has great edge detail, but does not have full density in the core.

Step 2. Do the soft Comp. Composite the foreground over the background with the soft matte. A partially transparent composite is expected at this stage.

Step 3. Create the "hard" matte. It can be made either by hardening and shrinking the soft matte or by pulling a new matte using more severe matte extraction settings to get a harder matte. Either way, the hard matte must be 100% solid and a bit smaller than the soft matte so that it does not cover the edges of the soft comp. You might want to even soften it a bit with a blur.

Step 4. Do the hard comp. Comp the same foreground again, but use the soft comp as the background. The hard matte fills in the solid core of the foreground, and the soft comp handles the edge detail.

...This information came from Steve Wright's Book "Digital Compositing for Film and Video." -pages 121 and 122.

[user_deleted]

I recently had the jittery hair problem and found that preprocessing with a lookup node helped. Use the colour picker to drag around in a good area of the matte right near the hair, drag the average into your colour swatches. Drag inside an area of the hair where the problem is, take the average of that and drag it into a swatch. Compare the RGB values which should be quite similar. Take the 2 green values lets say .4 for the screen and .32 for the hair and plot them on the lookup. Pull them apart so that they become .55 and .2. Do the same with the other 2 channels. Now your image should look more saturated around the edges and will key better most likely as long as the lighting on the hair doesn't change too much.

Good Luck
Pete

Thursday; December 21, 2006
2:03 AM

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