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Lesson 11. Alpha Channels and Masks > Creating an Alpha Mask

Creating an Alpha Mask

Director offers the Mask ink, which causes a bitmap to blend with the image below it pixel by pixel according to a separate reference map. This map, the mask cast member, behaves in a manner analagous to the alpha channel described earlier. A mask has two advantages: you can work entirely within Director, and you can use 8-bit images for the graphic plus a 1-bit image for the mask (resulting in a faster download time). The downside is that the image creation tools of Director are less comprehensive than the tools supplied by programs dedicated to creating graphic images.

The Mask ink, combined with a mask image, determines exactly which pixels of a sprite are transparent and which are opaque. In its simplest form, the mask is a black-and-white only image. The black areas of the mask make the corresponding pixels of the image opaque. The white areas make the image transparent.


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