 Color component

A color component is one numerical coordinate used by a color model to describe a colour. An RGB representation has red, green and blue components, while YCbCr has luma and two colour-difference components. Their meanings depend on the model and encoding: a component need not represent a separately emitted primary light. The Microsoft technical guide explicitly separates RGB signals from Y, Cb and Cr and gives their conversion equations.^[ref]

For an original normalized Linear-light RGB example, the triple $(0.20,0.40,0.80)$ contains three component values for one colour sample. Its blue component is $0.80$; that scalar alone does not specify the complete colour. A second triple $(0.70,0.10,0.80)$ shares that blue component while differing in red and green. Likewise, the same numerical triple interpreted in different color spaces need not describe the same physical colour.

A component is also distinct from a storage plane. An eight-bit packed pixel format can place three RGB component codes in three successive bytes for each pixel, all in one image memory plane. NV12M instead uses a luma plane and an interleaved colour-difference plane: two memory planes carry three color components. Chroma subsampling can additionally give the components different spatial sample counts.

An alpha channel describes transparency or coverage rather than another coordinate of the colour itself. PNG consequently distinguishes truecolour samples with red, green and blue components from truecolour-with-alpha samples that carry an additional alpha value.^[ref] Component identity, sample location, numerical encoding and storage layout together determine how an image is interpreted.