Color Theory and Measurement in Visual Perception and Textile Industry

Object Mode

Color perceived as belonging to an object.

Aperture Mode

Color seen as luminous light in isolation.

Surface Mode

Color perceived on a surface under illumination.

Volume Mode

Color perceived as occupying space.

Three Factors Required to Observe Object Color

Light source (Illuminant), Object (Spectral reflectance or transmittance), Observer (Human visual system).

Color Equation

Color = f (Illuminant × Object × Observer).

Additive Color Mixture

Red, Green, Blue → White.

Subtractive Color Mixture

Cyan, Magenta, Yellow → Ideally Black.

Typical Reflectance Curves for White

High reflectance across all wavelengths.

Typical Reflectance Curves for Black

Low reflectance across all wavelengths.

Typical Reflectance Curves for Grey

Flat intermediate reflectance.

Typical Reflectance Curves for Green

Peak around 500-560nm

Typical Reflectance Curves for Blue

Peak around 420-480nm

Typical Reflectance Curves for Yellow

High reflectance in mid + long wavelengths

V(λ) Function

Describes human visual sensitivity. Peak at 555 nm.

Photopic Vision

Cone-mediated, daylight vision.

Scotopic Vision

Rod-mediated, low-light vision (~507 nm peak).

2° Observer

Small foveal vision.

10° Observer

Larger retinal area.

Significant for large sample measurement

Chromaticity Diagram (CIE xy)

Shows hue and saturation independent of luminance.

Includes spectral locus and illuminant locus

Dominant Wavelength

Matches hue.

Complementary Dominant Wavelength

Applies if intersection is on purple boundary.

Color Appearance Attributes

Hue, Lightness, Brightness, Chroma, Saturation, Colorfulness, Excitation purity.

Tristimulus Values (X, Y, Z)

Computed from spectral data and color matching functions. Y represents luminance.

Color Matching Functions

Real (RGB) may include negative values; Imaginary (CIE XYZ) avoid negatives.

Perceptual Uniformity

CIExyY is not uniform; CIELAB is approximately uniform and used for ΔE.

Chromaticity Coordinates

x = X/(X+Y+Z), y = Y/(X+Y+Z).

Major Influencing Factors in Color Control

Materials, Methods, Machines, Measurement, Environment, People.

Cultural Connotations of Red

Passion (West), Luck (Asia).

Cultural Connotations of White

Purity (West), Mourning (China).

Cultural Connotations of Black

Elegance or death.

Cultural Connotations of Blue

Calm.

Cultural Connotations of Yellow

Optimism.

Cultural Connotations of Green

Nature.

Dominant Wavelength Definition

Defines hue.

Excitation Purity Definition

Defines saturation.

Y Value Contribution

Contributes to lightness.

Munsell System

Hue, Value, Chroma. Notation example: 5R 6/8.

Munsell System Advantages

Perceptually intuitive

Munsell System Disadvantages

Physical Samples may fade

NCS (Natural Color System)

Based on perceptual primaries (R, Y, G, B). Notation example: S 2050-Y90R.

NCS Advtanges

Perception-based design tool

NCS Disadvantages

Less suited for spectral calculations

High Excitation Purity

Vivid Color

Low Excitation Purity

Pastel

Standard Observer

Defined by CIE (1931 2deg, 1964 10deg)

Derivation of Standard Observer

Derived from color matching experiments, represents average human vision

Major Influencing Factors: Materials

Fiber type, dye quality, lot variation

Major Influencing Factors: Methods

Dye procedure, recipe errors, processing conditions

Major Influencing Factors: Machines

Calibration, maintenance, instrument drift

Major Influencing Factors: Measurement

Geometry, illuminant, observer selection

Major Influencing Factors: Environment

Lighting, humidity, temperature

Major Influencing Factors: People

Training, Visual differences

Hue

Basic color family

Lightness

Perceived reflectance

Brightness

Perceived intensity

Chroma

Strength relative to grey

Saturation

Colorfulness relative to brightness

Excitation purity

Distance from white to spectral locus