Apple Motion 4 - Manual (Page 241)

Note: Form objects, buttons, and JavaScript objects that are present in an imported PDF
file do not appear in Motion.
Multi-Page PDF Files
You can import multi-page PDF files. When you do, an additional parameter called Page
Number appears in the Properties tab when the PDF object is selected. A slider appears
and allows you to set which page is displayed in the Canvas. This parameter can be
animated to display different pages over time.
Important: Multi-layered PDF files are not currently supported. To import a multi-layered
illustration, export each layer as a separate PDF file and import these as a nested group
of objects in Motion.
More About Alpha Channels
Ordinary video clips and image files have three channels of information, one each for the
red, green, and blue channels. Many video and image file formats also support an alpha
channel, which contains additional information that defines areas of transparency. An
alpha channel is a grayscale channel where white represents areas of 100 percent opacity
(solid), gray regions represent partially opaque areas, and black represents 0 percent
opacity (transparent).
When you import a QuickTime movie or an image file into your project, its alpha channel
is immediately recognized by Motion. The alpha channel is then used to composite that
object against any other objects that are behind it.
There are two different ways of embedding alpha channel information into files, and
Motion attempts to automatically determine which type of alpha channel a particular
object uses:
• Straight: Straight alpha channels are kept completely separate from the red, green,
and blue channels of an image. Media files using straight alpha channels appear perfectly
fine when used in a composition, but they may look odd when viewed in another
application. Translucent effects such as volumetric lighting, or lens flares in a computer
generated image may appear distorted until the clip is used in a composition.
• Premultiplied: This type of alpha channel is multiplied with the clip’s red, green, and
blue channels. As a result, objects with premultiplied alpha channels always look correct,
even with translucent lighting effects, because the entire image is precomposited
against a solid color. Most commonly, premultiplied alpha channels are multiplied
against black or white, but Motion can also resolve alpha channels that have been
premultiplied against other colors.
241 Chapter 6 Creating and Managing Projects