# alpha channel

> English word · Noun

## Definitions
1. A numerical value specifying a level of translucency to be applied to a colour.

## Etymology
Coined by Alvy Ray Smith and Ed Catmull in the 1970s. Smith writes: "We called it that because of the classic linear interpolation formula αA+(1-α)B that uses the Greek letter α (alpha) to control the amount of interpolation between, in this case, two images A and B". That is, when compositing image A atop image B, the value of α in the formula is A's alpha channel.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/alpha-channel