Editing RGBA color model (section)

{{Short description|RGB color model with an opacity channel}}
{{redirect|ARGB|the colorspace developed by Adobe in the late 1990s|Adobe RGB color space}}
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[[File:RGBA comp.png|thumb|240px|Example of an RGBA image composited over a checkerboard background. alpha is 0% at the top and 100% at the bottom.]]
'''RGBA''' stands for '''red green blue alpha'''. While it is sometimes described as a [[color space]], it is actually a three-channel [[RGB color model]] supplemented with a fourth ''alpha channel''. Alpha indicates how opaque each pixel is and allows an image to be combined over others using [[alpha compositing]], with [[transparency (graphic)|transparent]] areas and [[spatial anti-aliasing|anti-aliasing]] of the edges of opaque regions. Each pixel is a [[4D vector]].

The term does ''not'' define what RGB color space is being used. It also does not state whether or not the colors are [[alpha compositing#premultiplied|premultiplied]] by the alpha value, and if they are it does not state what color space that premultiplication was done in. This means more information than just "RGBA" is needed to determine how to handle an image.

In some contexts the abbreviation "RGBA" means a specific memory layout (called [[#RGBA8888|RGBA8888]] below), with other terms such as "BGRA" used for alternatives. In other contexts "RGBA" means any layout.