Color space

In 1802, Thomas Young postulated the existence of three types of photoreceptors (now known as cone cells) in the eye, each of which was sensitive to a particular range of visible light.

[2] Hermann von Helmholtz developed the Young–Helmholtz theory further in 1850: that the three types of cone photoreceptors could be classified as short-preferring (blue), middle-preferring (green), and long-preferring (red), according to their response to the wavelengths of light striking the retina.

The relative strengths of the signals detected by the three types of cones are interpreted by the brain as a visible color.

In fact, such a definition had been given thirty years previously by Peano, who was thoroughly acquainted with Grassmann's mathematical work.

[5] As noted first by Grassmann... the light set has the structure of a cone in the infinite-dimensional linear space.

The resulting 3-D space provides a unique position for every possible color that can be created by combining those three pigments.

The RGB color model is implemented in different ways, depending on the capabilities of the system used.

The most common incarnation in general use as of 2021[update] is the 24-bit implementation, with 8 bits, or 256 discrete levels of color per channel.

Additional derivatives of CIE XYZ include the CIELUV, CIEUVW, and CIELAB.

CMYK stores ink values for cyan, magenta, yellow and black.

YIQ was formerly used in NTSC (North America, Japan and elsewhere) television broadcasts for historical reasons.

It is most commonly seen in its digital form, YCbCr, used widely in video and image compression schemes such as MPEG and JPEG.

They largely ignored blue light because the added complexity of a 3-component process provided only a marginal increase in fidelity when compared to the jump from monochrome to 2-component color.

The CIE 1976 L*, a*, b* color space is sometimes referred to as absolute, though it also needs a white point specification to make it so.

There are also likely to be rounding errors, especially if the popular range of only 256 distinct values per component (8-bit color) is used.

Those involved professionally with color matching may use viewing rooms, lit by standardized lighting.

A different method of defining absolute color spaces is familiar to many consumers as the swatch card, used to select paint, fabrics, and the like.