noun
alpha value
In computer graphics and image processing, the component that specifies opacity or transparency of a pixel, often used in the context of alpha channels.
See also: アルファチャンネル
この画像のアルファ値を調整して、背景を透けさせることができます。
You can make the background transparent by adjusting the alpha value of this image.
From English 'alpha' (the first letter of the Greek alphabet, used symbolically in computing) and 値 (value).