alpha channel

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alpha channel

An 8-bit layer in a graphics file format that is used for expressing translucency. The additional eight bits per pixel serve as a mask and represent 256 translucency levels from entirely clear (0) to opaque (255), with levels in between representing the degree of haziness. See translucency, RGBA and HSLA.

Not All Formats Have an Alpha Channel
The TIFF, PNG and WebP graphics formats support the 8-bit alpha channel, whereas JPEGs have none. GIF supports a 1-bit channel, which means that an area marked as alpha can be either transparent or not but no levels in between.

Layered graphics formats such as Photoshop's native PSD format can have many alpha channels while the image is being composed. When converted to another graphics format, the alpha channels are reduced to one or none depending on the destination format. See alpha blending.

Alpha Channels Allow Overlapping
The alpha region (checkerboard) was created in order to copy the purple and green elements onto the center image. In this example, the alpha channel allows individual elements to overlap other elements, functioning similar to drawing and CAD programs (see vector graphics and graphics).
References in periodicals archive ?
Taking web video to the next level, Flash Player 8 introduces support for 8-bit alpha channel video, allowing Flash developers to create innovative media compositions with interactive, semi-transparent video overlays over video, text, and graphics.
Titles have also been enhanced allowing users to import TIFF and TARGA images with alpha channel.
95) offers an in-depth coverage revealing core concepts on audio, alpha channels, manipulating time, and much more.
Users can now perform keyframeable image control and motion effects, as well as create transitions on up to two tracks of video and two tracks of graphics with alpha channels in real-time.
Key topics include: mastering complex animation and keyframe assistants; creating transparency with alpha channels, masks, and keying; transfer modes, track mattes, and effects tips and tricks; building nested compositions; working with fields, DV, NTSC, PAL, widescreen, and film; and more.
A special feature is the software's capability to handle multi-layer image-processing and 256-scale alpha channels in real time.
This SDK gives developers tools to support viewing files in the MrSID Generation 4 (MG4 [TM]) format, unveiled with the recent launch of GeoExpress 8, which adds support for multispectral data, alpha channels and improved mosaicking.