Figure 1: She's not been herself lately
©Rich Young, 1996
Rotoscoping and background removal can be easier than frame by frame methods and cheaper than bluescreening using Adobe After Effects 3.1. While Adobe Premiere has transparency tools, virtual clips and filters including extract and color replace, none of these will provide success if the source material has hard shadows caused by poor lighting. A combination of animated "garbage" masks and chroma keying in After Effects can make background replacement feasible even with bad video. Setting only the key-frames and letting After Effects calculate the in-betweens is much quicker than masking every frame of filmstrips or numbered picts in Photoshop. Feathering the mask and chroma keying the rest allows hair to have a more natural look. The method described here uses the standard version of After Effects and is appropriate for multimedia resolution. Higher resolution projects will use professional lighting and bluescreen work as well as the industrial-strength color-difference keys in the AE production bundle (or the improved Ultimatte plug-in). After Effects has numerous keyboard shortcuts, some undocumented, that also make work go much quicker. Only a few of these will be discussed here.
In AE 3.1 you can import media by dragging and dropping them into an
active project window. You can then drop the media into compositions icons
within the project window or drop them into the time layout or comp windows.
Opening the layer in the time layout window enables the masking tools (see
Figure 1). The pen tool is similar in operation to the pen tools in Photoshop
and Illustrator. It can create masks of straight-line segments and Bezier
curves that closely follow the shapes of organic objects. These masks can
be animated simply by setting a keyframe then adjusting the mask in each
frame where movements occur. To set a keyframe, access mask properties by
hitting "m" on the keyboard and clicking the time-vary stopwatch
next to "Mask Shape" (You can set a mask keyframe directly by
hitting option-m). AE will now automatically add a keyframe if the mask
is adjusted in another frame.
Figure 1: She's not been herself lately
The masking tools can take time to master but a few simple rules can
be picked up quickly. The pointer tool is activated by "Q" on
the keyboard. When the pointer tool is enabled the control key temporarily
activates the pen tool. The "G" key enables the pen tool. When
the pen tool is active the command key temporarily enables the pointer.
Clicking on layer adds a "corner" point. Click-again to create
another point. Click-drag adds a Bezier point with an active handle to control
the curve. Double-click completes a mask. The mask can be reshaped by moving
the control points with the pointer. The pen tool converts points to corner
or Bezier points. The curves can be adjusted with the pointer which controls
both handles at once or with the pen tool which alternately controls one
or both handles. You may find that you can set the mask more accurately
with the layer view magnified. This is done quickly by hitting command -
+ (same as Photoshop). Add enough control points here because adding or
subtracting points later will cause problems (interpolation occurs between
the masks' points). You can move the entire mask by selecting all and nudging
with the arrow keys or by command-dragging. Masks can be copied into any
layer frame, so you can store masks in library projects consisting of only
solids.
Hair is the key factor in deciding how to proceed. If the subject's hair
falls straight, a color key would not be necessary. The mask could be placed
just beyond the subject, feathered lightly (feathering occurs on both sides
of the mask) and adjusted in later keyframes if necessary. The feather property,
just below mask shape property (hit the "f" key to access), can
be set in a dialog box by clicking on the underlined numeric or with a slider
by command-clicking on it's name. Move along the time graph at regular intervals
to see if your mask needs adjustment. Remember, the pointer moves points
and controls both Bezier handles while the pen adds points and controls
either or both handles. Be sure not to add or delete points to avoid uneven
interpolation.
Figure 1 shows an instance where hair makes selecting the subject difficult.
In this case a crude mask could be drawn and animated in just a couple of
frames since the woman moved her body only a little. Since the mask renders
first, the shadow is eliminated thus simplifying a color key effect. Since
the remaining background (shown in Figure 2) is fairly uniform and the output
is multimedia resolution the standard AE color key filter can be used. Pick
a representative color with the eye dropper. Bring up the color tolerance
to make enough similar colors transparent and soften with a slight edge
feather (see Figure 3). After this you may need a little color correction.
If you need to sharpen your image, AE now has an unsharp mask filter just
like Photoshop's widely used unsharp mask. Finally, choose Effect>Image
Control>Levels to check the image's black and white points. Compression,
especially Cinepak, is much cleaner with even basic color correction (see
the Photoshop tutorial or Photoshop Classroom-in-a-Book for basics). If
you are delivering to Windows be sure to adjust the gamma (gray) level up
to 1.1 or 1.2 (adjust this down in Premiere). You can preview the setting
by turn off the Mac gamma adjustment in the Montors & Sound control
panel. You should to check this on a few Windows machines to be sure.
Figure2: Results of masking
Figure 3: With new background
As we've seen professionally-priced bluescreen studios and laborious frame editing can be avoided with the relatively simple tools provided in After Effects 3.1. Even so, planning makes every job easier. Remembering these things before shooting your video will produce great results in After Effects or Premiere:
The best news and support for After Effects is on the After Effects Forum
on AOL (keyword "CoSA"). It's a really great community that includes
many of the most knowledgeable users. Adobe tech support is present &
software updates are also there. If you use AOL try System Logs (under the
File menu) to record forum discussions to disk (just blast through with
the right arrow key), close the log and sign off. Also, there are also 2
internet mailing lists with light traffic.
The only book available as of June 1997 is Adobe's Classroom-in-a-Book.
The CIB series books are always good and this one is no exception. It includes
4 extra filter effects, good technical information, and many fun walkthroughs
-- even one with film resolution files. Information is sometimes available
in print. InterActivity (see esp. Chris Meyer's column) and 3D Design magazines
are reliable sources of useful information. Digital Video magazine now has
regular articles on AE topics by semi-regular columnists on the cutting
edge. See Trish Meyer's columns,
for example.
There are several class offered around the country. If you can afford
it, take American Film Institute
class from AE guru Trish Meyer. Another guru, Brian Maffitt, has video/CD tutorials that are quite good. Also,
I teach an Intro class at SFSU's
Multimedia Studies Program.
Even if you don't get the production bundle you'll want to check out the
3rd party plugs. Metatools' Final
Effects & Studio Effects bring high-end particle, lighting, distortion
& stylizing effects to the Mac. The Lens Flare Pack from Knoll Software
has several more lens flares including Warpflash for Star Trek (STNG) fans.
His new Custom Lens Flares will add customizable elements, motion-tracking
and obscuration. There is also Aurorix, Berzerk and Cyclonist from DigiEffects that add more even more lighting, brush, stylizing and distortion effects. Cogicon's TILT imports 3DMF models (Apple's QuickDraw3D format) that can be animated and rendered with lights and shadows. TILT can also use a grayscale layer to displace another layer in 3D space within AE!
Metatools, DigiEffects & Cognicon all have demos that you can download.
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Comments or suggestions welcome at RYoung097@aol.com