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Cut out existing footage

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Kyle ConnerCut out existing footage
by on Jun 8, 2010 at 4:52:43 pm

I created a 2 minute video for my boss, and now he wants to update it by cutting out the individuals who are speaking and put footage behind them like the were shot on a green screen. Does anyone know of a faster way then to create masks and attempt to cut out each individual frame?

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Dave LaRondeRe: Cut out existing footage
by on Jun 8, 2010 at 5:02:12 pm

[Kyle Conner] "Does anyone know of a faster way then to create masks and attempt to cut out each individual frame?"

Got AE 10, aka AE CS5? That's your only hope of speeding up the process, using a new feature called Rotobrush.

When you tell the boss it could take about two weeks of 8-hour days to isolate the people using rotoscoping -- which is what you're currently doing -- the prospect of an AE upgrade looks a little better.

You'll need a 64-bit operating system (Snow Leopard, Win 7) and enough RAM to assign 4GB to each core, plus more RAM if you want to actually run the operating system and keep other applications open.

Or the boss could opt for Plan B: "Forget about this newscast look, Kyle."

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

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Steve RobertsRe: Cut out existing footage
by on Jun 8, 2010 at 5:12:32 pm

FYI: CS5 works on Leopard, 10.5.7+.
I'm on 10.5.8 on a Macbook Pro and the trial runs fine so far.

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Jeffrey KaplanRe: Cut out existing footage
by on Jun 8, 2010 at 5:05:56 pm

Unless you have CS5 which features the new rotobrush tool - the only fast way to rotoscope is to do so EFFICIENTLY by "keeping your points to the joints."

In-Depth Tips on Rotoscoping:

Use as _few_ spline curve points as possible to mask the shape -- the less points you have to move, the less time the tedious process will take.

Create as few keyframes as possible to minimize edge jitter and retain fluid motion. If you set keys every frame, it's likely that you'll run in to jittery edges, though sometimes you _have_ to set keys every frame with fast motion. Depending on the source material, you may have a 30 frame clip to roto ... It may be conducive to start with a mask on Frame 0, then one on Frame 30. From that point you could add more keys at Frame 15. Then Frames 7 and 22, etc. (See Point 5 before you do this technique, though.)

Try to keep specific points in your mask corresponding to specific parts of your source material. For example, if you have three points that make up the armpit, elbow, and wrist joint of the edge of someones arm, make sure that you keep the armpit point going to the armpit in each frame. This can be difficult sometimes if there is a lot of movement, but if you don't stick to it, your points will "crawl" around the edges of the object and will cause funky edges and make you have to create more keyframes than is neccesary.

Use multiple masks to generate a matte. There is no reason to try and get the outside edges of a complex shape (such as a person) to fit all in one mask. Make seperate masks for the head, arms, torso, etc. as appropriate and add them together.

Try to pick "natural" keyframe points from the source material and fill add detail as needed. A basic example of this would be if you needed to cut out a person jumping on a trampoline. Obviously, your starting point for keyframes are at the apex and bottom of their jumps. Then you fill in more keyframes in between these points to make the mask more accurate. This is probably a better way to deal with roto than the aforementioned process of just cutting the clip in half over and over (the 0, 30, 15, 7, 22, etc. business) because it pays attention to the natural points of the clip that require keyframes.

Get some good music to listen to. Use the force. Try not to go crazy if you do it all day.

Side Note: A full two minutes of rotoscoping the full figure will take an unfathomable amount of time - you may want to discuss another alternative with your boss so you can enjoy your weekends. Reshooting the speakers in front of a green screen would take less time then rotoscoping a two minute clip.

Jeff Kaplan
Point 360 WEST
Animation & VFX Department

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Kyle ConnerRe: Cut out existing footage
by on Jun 8, 2010 at 5:16:24 pm

Unfortunately the subjects aren't able to be re-shot on a green screen. We now have a portable greenscreen to shoot newer subjects on, but of course he wants the old ones changed out. The technique I've been using is multiple masks with as few keyframes as possible, but was hoping there was a faster way. I'll look into CS5 and try to show him the savings. Thanks for the responses.

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Steve RobertsRe: Cut out existing footage
by on Jun 8, 2010 at 5:40:14 pm

[Jeffrey Kaplan] "Try to pick "natural" keyframe points from the source material and fill add detail as needed. "

This is sooooooo important. Watch the footage over and over to find those natural points. Any time "saved" by avoiding this step will be spent later on as you need to add more and more unnecessary keyframes.

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Michael SzalapskiRe: Cut out existing footage
by on Jun 8, 2010 at 7:56:07 pm

Great tips here!
Some more AE specific tips on rotoscoping available here
Such as:
  • Immediately after beginning to draw a mask, press Alt+Shift+M (Windows) or Option+Shift+M (Mac OS) to turn on keyframing for that mask and set a keyframe. This way, you won’t edit a mask frame-by-frame for several minutes (or longer) and then realize that you lost all of your work on previous frames because you forgot to click the stopwatch to make the mask path animated.
  • Draw your masks on a white solid layer with its Video (eyeball) switch off, above the (locked) footage layer. This way, you run no risk of accidentally moving the footage layer when you manipulate the mask, and you can also much more easily apply tracking data to the mask. (You apply the tracking data to the invisible solid layer that holds the mask.) This also means that you don't lose your cached RAM preview frames each time you manipulate the mask. (See Toggle visibility or influence of a layer or property group and Lock or unlock a layer.)
  • Turn on the Preserve Constant Vertex Count preference. (See Designate the first vertex for a Bezier path.)
  • When possible, transform (rotate, scale, move) the whole mask or a subset of the mask vertices instead of moving the vertices individually. This is both for efficiency and to avoid the chatter that comes from inconsistent movement across frames. (See Move vertices in free-transform mode.)
  • Manual motion tracking is less time-consuming than manual rotoscoping. The more effort you spend getting good tracking data for various parts of your scene and object, the less time you'll spend drawing and fine-tuning masks. (See Tracking and stabilizing motion.)

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

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