A 3 or 4 dimensional representation of chrominance and luminosity used
primarily for reproduction in media, or description of color. Some common
colorspaces for everyday applications are RGB, HSL, YUV, and CMYK.
Though extremely useful, L*u*v* and L*a*b* (developed by the
CIE) are less prevalent in modern tools
than other colorspaces. While RGB, HSL and others are computationally inexpensive,
they linearly represent components. As the responses of the human retina
are non-linearly related to light intensity (more like a logarithmic
response), this can lead to a non-uniform perceived difference for a unit change in
a linear colorspace (A change in a component value from 1% to 5% would appear, to
a standard observer, to vary color or luminosity more or less than a change from 91%
to 95%.). L*a*b* and L*u*v* are constructed to be perceptually uniform. The CIE settled on two standards with L*a*b* for
subtractive color (inks and dyes), and L*u*v* for additive color (lights). The
limited success of L*u*v* and L*a*b* can predominantly be attributed to the
suitability of gamma corrected RGB to most applications, as it is perceptually
uniform in luminosity.
Still, L*u*v* and L*a*b* are not the most elementary ways to represent color, as
they require a white point. As white is not concretely defined, all standard
colorspaces except XYZ are application specific. For default L*u*v* and L*a*b*
uses, the reference white is that of a black body radiator at 5000 degrees Kelvin.
As this is not required, two color values with identical component values in a
colorspace other than XYZ are not necessarily identical.