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 ?
The result of the eye-view ray march is a texture with a pre-multiplied alpha channel.
The transparent Alpha channel means the clips of actors and models permits content producers to insert their own backgrounds to create unique new scenes using their chosen greenlayers actors or models.
DoubleClick Rich Media and Video's Innovation Lab, a brain trust within DoubleClick that brings groundbreaking video and rich media technologies to life, developed two new Rich Media innovations - Video Button and Alpha Channel Video - which were successfully implemented to promote several shows featured in NBC's spring line-up and will remain in focus for the upcoming fall line-ups.
A new subtitle workflow that converts EBU format subtitle files to a flat movie with alpha channel.
In addition, this version offers alpha channel support for blue-screen type special effects as well as embedded cue points and global metadata options.
16-Bit SpectraMatte(TM) chroma keying - Real-time HD and SD chroma keying, enhanced with Avid's intuitive SpectraGraph(TM) UI and simultaneous alpha channel monitoring, gives professionals access to extremely responsive and high quality compositing tools.