CS426 Video 11 - Colour Physics and Chromaticity Diagrams

Flashcards covering key concepts from the Color Physics and Chromaticity Diagrams lecture, including color representation, the CIE diagram, color spaces (RGB, CMY, HSI), and related topics.

CIE 1931 Chromaticity Diagram

A diagram representing the range of colors visible to the human eye, useful for color specification and comparison.

Primary Colors

Red, Green, and Blue. When projected, their intersections create additional colors.

Complimentary Colors

Colors produced at the points of intersection of primary colors (Red, Green, Blue).

Color Creation

Using three sources of light (red, green, and blue), we can create the effect of nearly every color.

Color Channels

Multiple images created by a color camera, one for each sensor (e.g., Red, Green, Blue).

Negative Red Signal

A slight problem in color matching where some colors need to be matched by subtracting some red signal.

Colour matching functions

Functions showing the amounts of three primaries needed to match all wavelengths of the visible spectrum. Note the negative r values.

X, Y, Z color matching functions

CIE color matching functions that replace R, G, B. Y is also designed to be equal to the luminous efficiency function of the eye (measures Intensity).

P(λ)

Spectral response of source we would like to match.

C

The color our eyes will see when viewing spectral response P.

Colour representation

The response of the retina to a colour can be created by a weighted combination of just three colour intensities.

X

Red Signal

Y

Green Signal

Z

Blue Signal

Chromaticity Values (x, y, z)

Values that are independent of intensity. x = X/(X+Y+Z), y = Y/(X+Y+Z), z = Z/(X+Y+Z)

Chromaticity Diagram

A diagram produced by setting X+Y+Z=1 and viewing the plane produced, which gives a representation of visible colours. x, y values.

Monitor Gamut

Displayable colors for a monitor, usually inside a triangle on the chromaticity diagram.

Spectral Locus

The boundary formed by all monochromatic (spectral) sources on the chromaticity diagram. Horse-shoe shaped.

Line of Purples

The locus on the edge of the chromaticity diagram formed between extreme spectral red and violet; contains non-spectral colors.

Gamut

A triangle formed by three points on the boundary of the chromaticity diagram, representing the range of colors that can be recreated using those sources.

RGB Colour Space

A linear colour space that uses single wavelength primaries. Based on additive primaries, Cartesian coordinate system, Black at the origin, Gamut depends on LCD/Phosphors.

Adative Primaries

By adding weighted combination of Red, Green and Blue light most colours can be reproduced. This technique is used on CRT screens.

CMY (Cyan,Magenta,Yellow) Colour Space

C=G+B, M=R+B, Y=R+G and W=R+G+B thus C=W-R M=W-G Y=W-B also W=W+W because ink can’t make the paper more reflective

Subtractive Primaries

Methods used in printing, in practice it is very difficult to obtain a good black using CMY inks only so a black ink is also used.

HSI (Hue, Saturation, Intensity) Colour Space

A color space defined by Hue, Saturation, and Intensity.