Digital Image Processing Color Models

This set of vocabulary flashcards covers electromagnetic spectrum basics, human visual system components, and various hardware- and image processing-oriented color models like RGB, CMY, CIE XYZ, CIE Lab, HSV, and YCbCr.

Visible Spectrum

The range of electromagnetic radiation visible to humans, spanning from $400\,nm$ (blue) to $700\,nm$ (red).

Rods

Photoreceptors in the human visual system responsible for perceiving intensity.

Cones

Photoreceptors in the human visual system responsible for color perception.

RGB Model

An additive color model (Red, Green, Blue) used for displays and monitors where an image consists of three color bands.

CMY Model

A subtractive color model (Cyan, Magenta, Yellow) used primarily in paper printing, where the conversion from RGB is defined as $\begin{pmatrix} C \\ M \\ Y \end{pmatrix} = \begin{pmatrix} 1 \\ 1 \\ 1 \end{pmatrix} - \begin{pmatrix} R \\ G \\ B \end{pmatrix}$.

CIE XYZ Model

A 3D color model defined by the Commission Internationale de l’Eclairage based on the chromatic response of the eye using three standard primaries: $X$, $Y$, and $Z$.

Luminance (CIE XYZ)

The component $Y$ in the CIE XYZ model, which contains all the intensity information and matches the sum of the three human cone responses.

Normalized CIE Coordinates

Values calculated such that $x = \frac{X}{X+Y+Z}$, $y = \frac{Y}{X+Y+Z}$, and $z = \frac{Z}{X+Y+Z}$, resulting in the property $x + y + z = 1$.

CIE Lab (Lab*) Model

A color model with one luminance channel ($L$) and two color axes ($a$ and $b$), useful for measuring small color differences in industry.

a axis (CIE Lab)

The color dimension extending from green ($-a$) to red ($+a$).

b axis (CIE Lab)

The color dimension extending from blue ($-b$) to yellow ($+b$).

HSV Model

A color space representing Hue, Saturation, and Value; it is intended to be a perceptual space suitable for art, recognition, and minimizing illumination change effects.

Hue (H)

The color component of the HSV model encoded as an angle from $0$ to $2\pi$; for example, $0^{\circ}$ to $60^{\circ}$ represents Red.

Saturation (S)

The component of the HSV model describing the percentage of the color.

Value (V)

The component of the HSV model representing the intensity of the color.

YCbCr Model

A fast-to-compute model used in digital TV and compression where $Y$ is luminance, $Cb$ is blue-difference, and $Cr$ is red-difference.

rgb2hsv

A Matlab Image Processing Toolbox function used to convert RGB color values to the HSV color space.

Color Slicing

An image processing technique, often performed in the HSV space, used to assign different colors to the foreground versus the background based on specific Hue values.