□□The Alpha Extract/Create button and its associated menu item will change depending on whether only a background movie is open, or both a background and a foreground movie are open.
When only a background movie (32-bit, with alpha channel or a 24-bit chromakey movie) is open, the Extract Alpha function is available.
When both a background and a foreground movie are open, the Create Alpha function will be available.
Extracting Alpha Channel Information
To extract the alpha channel of a QuickTime movie or to create an alpha channel from a chromakey movie, simply open the movie using the Open command from the File menu.
MovieTools creates a new movie of either 8-bit greyscale depth or 24-bit RGB depth, according to the preferences you set, as described below. With 24-bit RGB movies, the alpha channel information is duplicated in the red, green and blue channels.
Once the movie is open, select the Extract Alphaﾉ item from the File menu or click the Extract Alpha button in the main window.
If the movie is a 32-bit movie, MovieTools will open a file save dialog.
If the foreground movie is a 24-bit movie, MovieTools will open a palette that provides a set of control for adjusting chromakey settings.
The chromakey alpha channel function is designed to work from a reference frame that is completely clear, showing only the chromakey background color. The reference frame can either be the first frame of the foreground movie, or you can load a movie or a PICT file as the reference. If you load a movie, the first frame will be used as the reference frame. If you select the ﾒLoad Ref. Frameﾓ button, the ﾒOKﾓ button will change to read ﾒLoadﾓ. Once you load a reference movie or PICT, the button will change back to ﾒOKﾓ, and the reference option buttons will be disabled.
The chromakey function can also work without a reference frame, although the results will probably not be as good as with one, and the process will operate much more slowly. We strongly recommend using a reference frame; the ability to work without one is provided simply for completeness.
The Chromakey alpha palette also has text fields for Hue, Saturation and Brightness, along with fields for Hue, Saturation and Brightness Tolerance settings. If you move the cursor to the preview display, it will change to an eyedropper. You can click anywhere on the image to set the Hue, Saturation and Brightness settings, and the type in a range for Tolerance.
You can also click and hold down the mouse button to drag over the image to set a Tolerance. While you drag, MovieTools will track the high and low Hue values to compute a Tolerance setting. When you release the mouse button, the Hue value will be set to the middle of the Tolerance range. When you click the OK button, MovieTools will open a file save dialog.
MovieTools will automatically append ﾒ.Alphaﾓ to the original file name, but you can rename the file if you wish. When you click on the Save button in the file dialog, MovieTools will begin extracting the alpha channel from the original movie. At the bottom of the window it will show the frame numbers it is currently processing.
In the Preferences dialog, selected from the Edit menu, you can select either 8-bit greyscale or 24-bit RGB for the output movie. You can also set MovieTools to invert the alpha channel in the new movie.
The Alpha Extraction function supports 24-bit chromakey movies with a solid color background or 32-bit depth movies with the alpha channel information in the upper 8 bits.
Creating An Alpha Channel
To create an alpha channel movie for a background movie, start by opening the background movie, using the Open command from the File menu.
Once the background movie is open, the Open Foreground Movie menu item will be enabled, allowing you to open a movie from which the alpha channel will be created.
Once the foreground movie is open, select the Create Alphaﾉ item from the File menu or click the Create Alpha button in the main window. MovieTools will automatically append ﾒ.A32ﾓ to the original file name, but you can rename the file if you wish. When you click on the Save button in the file dialog, MovieTools will begin extracting the alpha channel from the original movie. At the bottom of the window it will show the frame numbers it is currently processing.
If the foreground movie has an alpha channel, or is an 8-bit movie, the alpha channel information or the 8-bit image is copied into the output movieﾕs alpha channel, while the RGB information of the output movie will come from the background movie.
If the foreground movie is a 16- or 24-bit movie, the average of the red, green and blue channels is converted to 8 bits and copied into the output movieﾕs alpha channel.
The output movie is always created as a 32-bit movie with an alpha channel, regardless of the bit depth of the background movie.
#□□□□↵□□□□□□□□□□□□□□↵□□□□□□□□□□□□□□↵□□□□□□□□□□□□□･↵□□□□□N N □□□ﾉ↵□□□□□□□□□□□□□S↵□□□□□□□□□□□□□W↵□□□□□□□□□□□□□i↵□□□□□□□□□□□□□m↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□ﾅ↵□□□□□□□□□□□□□ﾒ↵□□□□□□□□□□□ﾔ↵□□□□□□□□□□□ﾖ↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□^↵□□□□□□□□□□□□□i↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□↵□□□□□□□□□□□↵ﾒ↵□□□□□N N □↵ë↵□□□□□□□□□□□□□W↵□□□□□□□□□□□□□[↵□□□□□□□□□□□□□m↵□□□□□□□□□□□□□q↵□□□□□□□□□□□□□ ↵□□□□□□□□□□□□□ｵ↵□□□□□□□□□□□□□L↵□□□□□□□□□□□□□Y↵□□□□□□□□□□□□□□↵□□□□□□□□□□□□□↵□□□□□□□□□□□□□/↵□□□□□□□□□□□□□3↵□□□□□□□□□□
