Alphakanaal

Alphakanaal, or alpha channel, is a component of digital images that encodes per-pixel transparency information. It enables rendering of translucent objects and smooth compositing of multiple image layers by providing an opacity value for each pixel.

In standard color models, pixels have red, green, blue channels; when an alpha channel is added, the pixel is represented as RGBA. The alpha value usually ranges from 0 (fully transparent) to 255 (fully opaque) in 8-bit images; higher bit depths exist. Premultiplied vs straight alpha: in premultiplied, RGB values are stored after being multiplied by alpha.

Common formats: PNG and TIFF support alpha; JPEG does not. GIF supports binary transparency. WebP and AVIF support alpha; some video formats and image sequences also carry alpha. File ordering of channels (RGBA, BGRA) varies by format and API.

Applications: Used in image editing, UI design, game graphics, film and video post-production, web graphics, where layers are composited. Alpha channels allow masks, feathering, and translucency.

History: Concept matured with early computer graphics; PNG (1996) formalized an 8-bit alpha channel; widespread adoption in image editing and web. Transparent GIF predated PNG with limited transparency.

See also: Alpha compositing, RGBA, Transparency, Premultiplied alpha.