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Bad blue screen key - How to get rid of edges without losing detail?

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Peter Mayer
Bad blue screen key - How to get rid of edges without losing detail?
on Jul 13, 2012 at 9:22:43 pm

Hey guys

We are having trouble with keying our original footage shot on Digital HD 1080i with Keylight on After Effects. As you can see in the images below, we have a live-action plate with superheroes and a very light digital background plate in a UFO.
We have tried out some Andrew Kramer tutorials, but the problem is as follows:
If we shrink our matte, we lose details, especially on the neck area of the red hero, which results in a deformation from the shoulders up. If we do not do that then we get a blue spill in that area.
We also tried to pre-blur the matte, but then the edges around the actors got too soft and seem unrealistic as well.

We have achieved good results on the other areas but it's always with a tradeoff: If the body is good, the neck area is bad and the other way around.
Also using the clip-black/clip-white settings seem unhelpful to cover all areas.
Additionally we want to keep the shadows that are cast on the bluescreen floor.

So here are our questions:

Is there any way to optimise the picture before we go into the keying process?

Is there anything we missed in our efforts? Could you direct us to another good tutorial that focuses on how to retain detail in the edge area?

We would be grateful someone would share some of his or her expertise in that area.

Best wishes
Pete and Torsten









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mathew fuller
Re: Bad blue screen key - How to get rid of edges without losing detail?
on Jul 14, 2012 at 6:08:50 am

Basic principal behind keying. To get a great key in many cases u need multiple instances of ur keyer on one movie clip.

Often u will key the hair with one, the body with another, the facial features with another. This takes patience and often some masking. Dont try to do it all with one instance if ur keyer and u will be fine.

My Work:
http://www.morecompletefx.com


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mathew fuller
Re: Bad blue screen key - How to get rid of edges without losing detail?
on Jul 14, 2012 at 6:09:53 am

Forgot to say. Also u need a keying plugin set like keycorrect from red giant. Essential stuff.

My Work:
http://www.morecompletefx.com


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Peter Mayer
Re: Bad blue screen key - How to get rid of edges without losing detail?
on Jul 14, 2012 at 9:05:58 am

Dear Matthew

Thank you! Yeah we tried to work with multiple instances, but probably need to invest more time in that. So basically you say that we should use one key in e.g. mask 1, the next in mask 2 etc.?

We will also look into keycorrect.

Thanks again, we will post updates on our progress tomorrow.

Cheers,
pete and torsten


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Darby Edelen
Re: Bad blue screen key - How to get rid of edges without losing detail?
on Jul 22, 2012 at 10:14:46 pm

I'd recommend refreshing yourself on Keylight by giving the documentation a read through. Lots of good information in there. If you google search for "keylight documentation" there should be a PDF result from The Foundry.

You may not need to mask separate sections of this image in order to get a good key. However, you definitely will need to key it at least twice, maybe even three times. With your particular image I saw much better results using a lower Screen Balance value (around 50).

While adjusting these properties I recommend viewing the 'Status' which will show you all fully transparent (black), fully opaque (white), and semi-transparent (gray) areas.

Key once for the edges, preserve softness (but don't add any) and don't worry about "holes" in the foreground subject. This instance of Keylight won't need much adjustment in the Screen Matte section.

Key again for the core of the foreground subjects, this is where you'll use Clip White to make sure the foreground is solid. Since this instance is only for the core of your foreground subject, use Screen Shrink to erode the matte by a pixel or two.

The combination of these two mattes should be good enough for your main subjects. I would usually just lay the edge key layer on top of the core key layer unless more complex work is required.

If you need a better shadow key then you could do that separately as well. Most likely your edge key will preserve the shadows pretty well, so you could simply duplicate that and make some adjustments to preserve more shadow. If you'd like to avoid color spill in the shadows I'd recommend just using Generate > Fill with a black color

Also you'll likely need to use the Despill Bias to remove blue spill from your subjects. I like to click to open the color picker and then use the eye dropper from there to select a foreground color (try a point in skin of your subject) for this operation.

Darby Edelen


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