Color Models

A color model is a method for explaining the properties or behavior of color within some particular context.

No single color model can explain all aspects of color

Properties of Light

Light is a narrow frequency band within the electromagnetic spectrum

Other frequency bands in this spectrum are AM radio, FM radio and TV, Microwaves, Infrared, Visible, Ultraviolet and X-rays.

Band spread from 10^4 to 10^20 Hz with light being in the order 10^14.

Each frequency value within visible band corresponds to a distinct color. Red lowest freq of 4.3 x 10^14 Hz and Violet highest freq of 7.5 x 10^14 Hz. (VIBGYOR).

Light being an electromagnetic wave has an associated wavelength and frequency; both being inversely proportional.

c = W x F, c is speed of light.
W and c are material dependent and F is constant for all materials.
c = 3 × 10^8 m/s

Light wavelength being small, Angstrom (1A = 10^-8cm) or nanometers (1nm = 10^-7cm) units are used.
Red wavelength is 700 nm and violet is 400 nm

Color = emitted freq + reflected freq

Dominant frequency determines the color of the light, also called Hue

Brightness is another characteristic of light. It is the perceived intensity of light. Intensity is the radiant energy emitted per unit time, per unit solid angle, and per unit projected area of the source. Radiant energy is related to luminance of the source.

Yet another perceived characteristic is Saturation or Purity. Purity describes how washed out or how pure the color of the light appears. Pastels and pale colors are less pure.

Chromaticity is used to refer collectively to the two properties describing color characteristics: purity and dominant frequency.

Energy emitted by white light source has a distribution over the visible frequencies with each frequency component contributing more or less equally to the total energy.

Dominant frequency Ed is shown as a spike in energy distribution curve.

Brightness is area under the energy distribution curve. It is the total energy density emitted.

Purity is difference between Ed and Ew. More Ed means more purity. Ew = 0 then purity is 100% and purity is 0% when Ed = Ew.