In the September issue, we showed you how to build a green screen, then use chroma-keying to trim the subject out of a green-backed video clip to place that subject on a different background clip (Make (and Use) Your Own Green Screen). This month we’ll show you how to get a handle on synchronizing everything between two clips visually and along the timeline, plus color-keying tricks to help you make fun, easy work out of green-screen compositing.
WHAT YOU NEED
> Final Cut Express ($299) or Final Cut Pro (as part of Final Cut Studio, $1,299)
The Interface (as shown above)
1. Browser. Your imported video clips and Final Cut Sequences live here under Project tabs; the Effects tab contains all of Final Cut’s audio and video filters and transitions. Use the icons to change from list to thumbnail view for easy clip identification.
2. Viewer. Double-click a clip to load it into the Viewer and select the Filters tab to access the configurators for that clip’s filters; click the Motion tab to move or resize clips in the frame.
3. Canvas. Preview your composition here, using the Scrubber to scrub or the control buttons to navigate through the frames.
4. Timeline. Drag clips here to get started. The bottom track (V1) is the background, and you can stack as many as 98 more tracks sequentially above it. Final Cut automatically rips the clips’ audio tracks to the Timeline’s lower section.
5. Toolbar. More for celluloid-style film editing, the tools won’t do anything to clips in the Viewer window until you select View > Image + Wireframe to activate Wireframe mode.
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1. Set the Stage
Launch Final Cut and use the default new project that opens with the app, or select File > New Project. Import all of your footage for the project by dragging files into Final Cut’s Browser, and then save your project (if you don’t save it at this point, Final Cut will prompt you that it can’t perform its auto-save magic until you do). Drag the background clip into the Timeline’s V1 track and drag the foreground clip into V2.
You can jump right into the effects now, but eventually you’ll want to reposition the start and end points of the clips or edit them for length (hint: use the Razor Blade tool). Click and drag to move the clips along the Timeline, and for precise placement, highlight the clip and press Option and the left or right arrow key to move one frame at a time. When trimming clips for length, just activate the Razor Blade and click on the clip in the Timeline; highlight the scraps and press Delete to remove them. To manipulate the video in the frame, select View > Image + Wireframe and use the Selection and Crop tools to manipulate the image in the Viewer window.
Press Option-left Option-right arrow to nudge a clip along the timeline; View > Image + Wireframe puts adjustment handles on your clips.
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2. Mask Out the Parameter
If your green screen came up a little short and/or uneven (as ours did), use a matte filter to remove non-green sections of the background before applying the color key. Doing so will save you lots of time futzing with the Color Picker and will result in a cleaner, better-looking composite. Double-click the foreground track in the Timeline to load the clip into Final Cut’s Viewer window.
Now click the Browser window’s Effects tab and scroll down to the Matte section - we used the Eight-Point Garbage Matte. Click and drag the effect’s icon onto the clip (either in the Timeline or Viewer window, both ways work) and press the Viewer window’s Filters tab to access the Matte controls. Click the plus-sign icon for Point 1 and use the resulting crosshair cursor to drag the onscreen point 1 (in the Canvas window), and repeat for all eight points to block out the rough edges. Don’t forget to scrub through the entire clip to make sure the matte fits.
If you have too much background garbage to fit in an 8-point matte, you can always add more matte filters.
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3. Key Out the Color
Knocking out the green background is done with Final Cut’s Chroma Keyer. Double-click your foreground clip in the Timeline to load it into the Viewer window. Now scroll down in the Effects Browser window to the Key Effects and drag the Chroma Keyer icon onto the clip in the Viewer window or in the Timeline. Open the Viewer window’s Filters tab and find the Chroma Keyer’s configurator. Click the button labeled Visual to get to the magic Eyedropper - click its icon and then click on the color (in the Canvas window) that you want to remove.
Missed some? Press the Shift key while clicking some of the remaining background color with the Eyedropper to add to your already selected color (a non-Shift-click will pick a new color instead). Then fiddle with the sliders to adjust the edge’s thickness and sharpness, and if you still don’t like the results, click the Numeric button. As with any video effect, you’ll want to play or scrub through the clip to make sure the background is gone throughout - lighting changes in the clip can tweak the color enough to thwart the Chroma Keyer, but you can add the colors to the key out by returning to the configurator and Shift-clicking color scraps with the Eyedropper.
You can adjust the Color, Saturation, and Luminance bars for a perfect match - or use the Shift-click Eyedropper to auto-match every drop.
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4. A Little (More) Fire, Scarecrow?
Our fire dance would look way hotter with an extra layer of flames in front of the subject - and it’s easy to add them. Just drag the same (or a different) clip from the Browser to an empty track above the two tracks (V1 and V2) that are already there. Final Cut will designate track V3 and the new clip will appear as the top layer in the Canvas window, blocking the other layers - but that’s OK, we’ll remove most of the image anyway, down to just some flames.
Drag the Chroma Keyer onto the clip as before and use the Eyedropper tool to pick up the colors you want - orange and yellow in our case. The trick here is to invert the key, removing everything except the selected colors. To do that, just check the Invert box at the bottom of the Chroma Keyer’s Numeric control pane. Don’t forget that you can hide other layers to get a better look at what you’re working on. Just click the blue Visibility button at the far-left side of any clip in the Timeline.
Checking the Invert box removes everything but the keyed colors.
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5. Move Stuff Around
Final Cut’s motion controls are an excellent weapon in your war on bad footage. To get things moving, load a clip in the Viewer window (double-click it in the Timeline and select the Motion tab). Move the Timeline playhead to the beginning of the sequence and click the Add Motion Keyframe icon on the Canvas window, then move the playhead to where you want the character to stop shrinking (or any other motion to stop) and add another motion keyframe.
With the playhead still on the second motion keyframe, use the Viewer window’s Motion controls to tweak logistics like rotation, scale, in-frame position, cropping, distortion, and more. The effect will gradually take place in the time between the two motion keyframes. Any changes you make to frames along the Timeline will alter every frame back to the previous motion keyframe on the Timeline—but you can add all the motion keyframes you want to control the backspill.
Motion keyframes are retroactive, so always make a new motion keyframe before you start tweaking the motion.
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GO WIREFRAME
If you want to make wholesale changes to a clip’s placement, zoom level, cropping, distortion, etc, that don’t change over time, forget motion keyframes. Select View > Image + Wireframe to activate the Wireframe handlers, whereby you can manipulate the active clip.
