Collage (The Digital Advantage) - Frame-by-Frame Stop Motion: The Guide to Non-Traditional Animation Techniques - page 132

where there is enough fill light in the dark areas. This way you have the
important detail from the image that you can color and contrast correct after
you have the whole composite image put together.
Fig 10.4 Objects that have been
blended together with flat
lighting.
The other important element to consider when combining images is the
placement and “eyeline” of those images or figures. Once you place various
images together in one frame, you want to know if they have a relationship to
each other based on their visual connection and image dialog. If you had two
people being animated separately and you had to put them together, would it
feel like they were addressing each other? One way to gauge this relationship
is to take the most difficult element or person to animate of the composite
and animate it. You can then import this movie into the rotoscope function
of a program like Dragon. When you animate the second element or person
for the composite, the rotoscope function allows you to onionskin or ghost
each frame from the initial footage to each frame of your new animation. You
can see where your new object or person needs to be adjusted, so it has a
relationship with the initial image or person for every frame you animate. This
makes your final composite much more controllable.
One element that can help sell the composite technique is the shadow of the
composited image. It is often difficult to take the shadow of an image, cut it
out, and blend in with a new image. This is because the shadow is not solid,
and when it is cut out, it brings with it the image of the area that it is shading,
which may not blend into your new composite. One solution that many
composite artists use is to create a new shadow for the cutout composite
image in After Effects or Photoshop. The trick they use is to copy the layer
element (of your composite image), flip it, and place it below the original
object or element. Turn the copy black and lower the opacity to 20 or 30%.
Then you need to transform it and angle it so it looks like it's on the ground or
wherever it needs to fall naturally in the new composition.