A pixel is a set of channels defining the color at a given point in an image.
Conceptually, a pixel is little more than a color base whose elements model
ChannelConcept. Many properties of pixels inherit from color bases: pixels may be homogeneous if all of their channels have the same type; otherwise they are called heterogeneous. The channels of a pixel may be addressed using semantic or physical indexing, or by color; all color base algorithms work on pixels as well. Two pixels are compatible if their color spaces are the same and their channels, paired semantically, are compatible. Note that constness, memory organization and reference/value are ignored. For example, an 8-bit RGB planar reference is compatible to a constant 8-bit BGR interleaved pixel value. Most pairwise pixel operations (copy construction, assignment, equality, etc.) are only defined for compatible pixels.