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Chromakeying: When to Rotobrush?

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Ian RosaaenChromakeying: When to Rotobrush?
by on Apr 3, 2013 at 2:11:15 pm

1. Adobe has a keying tutorial,, in which they suggest using the Rotobrush as a "best practice."

I've not seen the Rotobrush suggested in any other keying tutorial. My guess is that rotoscoping may do a better job than using Keylight alone, provided one has the time.

2. Adobe's tutorial did not address edge problems. If one used the Rotobrush, would one fix the edges as suggested in

Thank you.

Ian Rosaaen

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Dave LaRondeRe: Chromakeying: When to Rotobrush?
by on Apr 3, 2013 at 2:30:31 pm

Well, I view Rotobrush as a last resort for problem chroma key footage.

There's no good substitute for a chroma key shot that:
1) has adequate separation between subject and background to minimize light spill,
2) is lighted properly with separate lighting on subject and background with no hot spots and a couple of stops darker than the foreground,
3) uses as featureless background as possible (no wrinkles, cracks, etc.), and
4) is recorded in a video codec that retains good color resolution (aka color sampling).

Even if all those conditions are met, sometimes you just have to build yourself a matte using various layers, animated masks keying to separate the subject from the background, and in those instances Rotobrush will help a lot.

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

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Ian RosaaenRe: Chromakeying: When to Rotobrush?
by on Apr 3, 2013 at 3:16:53 pm

Excellent. Thank you.


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Todd KoprivaRe: Chromakeying: When to Rotobrush?
by on Apr 3, 2013 at 8:43:31 pm

The Roto Brush tool is a great way to make really tight garbage mattes, which are often the only way to make a keying job manageable (especially if the green screen is uneven in color or lighting).

Using the Roto Brush tool is just a more modern way of getting a super-tight garbage matte as is suggested here:
That old video just uses Auto-Trace, because it came out before Roto Brush existed.

Todd Kopriva, Adobe Systems Incorporated
After Effects quality engineering
After Effects team blog

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Ian RosaaenRe: Chromakeying: When to Rotobrush?
by on Apr 7, 2013 at 4:02:28 pm

Thank you all for your help.

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Roland R. KahlenbergRe: Chromakeying: When to Rotobrush?
by on Apr 5, 2013 at 4:52:25 pm

The Rotobrush is not an ideal choice for creating chroma screen mattes because it's too slow. Auto-trace is just slightly faster.

To create tight junk mattes quickly -

1) apply multiple instances of Color Key until you've removed all the green/blue. Start with an instance of Color Key that is furthest away from the subject. As the colors get keyed out, work your way into the subject area. Set Color Tolerance to about 15 and the Feather and Thin properties to about 5 each.

Do not be concerned if you key into the subject. These areas can be retrieved by applying Simple Choker with a negative value -which will be done in the next step.

2) When you have keyed all the color and reached the subject,
apply Simple Choker and set its value to -25 (or a value that makes the green/blue visible. You will end up with your subject enclosed by a green/blue outline.

By creating a tight junk matte such as this, you will only have to key out a smaller area. This makes the keying task easier for the keying plugin as it will very likely have fewer stray (colored) pixels to work against.

3) Apply Keylight and pickwhip on the green/blue. As you hover over the Comp Panel, hold down the CTRL key to sample the underlying color from a wider area - you will notice the eyedropper increase in size when you do have the eyedropper in the Comp Panel and the CTRL key is held down. As you hover, add the ALT key to get a preview of the area that will be keyed.

Hover over until you find the spot that gives you the best key. This is an extremely important part of the keying process - picking the best spot to select the keying color.

4) When keying, look at creating at least two mattes (a) a core matte and an (b) edge matte. You are looking at two keying passes, one for each matte.

With the next version of AE, you may want to look at using Refine Edge to create edge mattes. More info on Refine Edge here >


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Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects ACE/ACI (version 7)

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Ian RosaaenRe: Chromakeying: When to Rotobrush?
by on Apr 8, 2013 at 2:25:18 pm

Wow! Good stuff. I'll study it. Thank you.


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Ian RosaaenRe: Chromakeying: When to Rotobrush?
by on May 12, 2013 at 3:39:00 pm


I've done everything up to, "Apply Keylight and pickwhip ..."

I don't know how the pick whip would be applied. Will you please elaborate?

Thank you.


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