25 July 2010
An alpha channel in Adobe Flash Professional stores matte information in order to support transparency. In a 2D image or video element, each pixel stores a color. To add transparency, additional data is stored in the alpha channel with a value between 0 and 1. A value of 0 means that the pixel does not have any coverage information and the result is transparent; a value of 1 means that the pixel color value is completely covered and the result is opaque.
PNG is the only cross-platform bitmap format that supports transparency (as an alpha channel).
When exporting a PNG file, the settings in the Colors section are the same as the Bit Depth option in the PNG Publish Settings tab. Flash sets the number of bits per pixel to use in creating the image based on the export settings:
When you set the publish settings to export PNG files, you can choose from the following options:
Note: The higher you set the bit depth setting, the larger the PNG file's size will be when exported.
The FLV video format also supports transparency if the alpha channel data is included at the time of compression and if a video codec that supports transparency is used. The F4V video format does not support alpha video channels, and therefore F4V video footage cannot be transparent.