Color

Understanding Color● What is a color?● How is color perceived?● How can color be represented?

Blackbody Radiators● A theoretical model

of how objects emit radiation based on temperature

● Examples– Incadescent light

2854K

– Direct sunlight4874K

Importance of Color● Painters first used

charcoal

● Early artists used ochre to add red

● Colors are not always the same from culture to culture

Emotional Response to Color● Temperature is

associated with colors– Blue is cold

– Red is warm

● Depends on overall scene illumination

Thomas Young● English Physician

– 1773-1829

● Every color can be matched by adding three primaries

Hermann Helmholtz● German Scientist

– 1821-1894

● Verified Young's theory by identifying three types of receptors in the eye in 1852-3

● Invented opthalmoscope

Retinal Structure

● Eye has photoreceptors for 3 colors

Color Vision● Each cone type is

sensitive to a different range

● Research indicates we can see about 10 million colors

● How can one color be distinguished from another?

● How are colors specified?

Color Vision● Depends on relative

stimulation of photoreceptors

● Depends on wavelength

● Monomers– Same colors

– Different spectra

● Color depends on surrounding colors

Color Deficiency● About 10% have

some deficiency– 9% men

– 1% women

– Most missing red or green cones

● Red and green percieved as brown

● Monochromats have only rods

● Dichromats have 2 of the three cones

● Low light vision is not affected

● Care needs to be taken when creating visual materials for others– Web pages

– Brochures

– Design in black and white, then add color

Color Blindness● Protanopia

– No red cones

– Red, orange, and yellow are shifted toward green

– Violet is shifted towards blue

– severe cases● traffic lights are black● Purple flowers are blue● Problems in extreme lighting

conditions

Color Blindness● Deutanopia

– No green cones

– Green, yellow, and orange are shifted toward red

– Poor discrimitation of blues

Color Blindness● Tritanopia

– No blue cones

Color Blindness

Ishihara Tests

Quantifying Color● CIE

– Commision Internationale d'Eclairage

– began work in 1931

– First chart in 1947

CIE Chart● Revised in 1976

● Spectral colors (pure tones) are around perimeter curve

● Purple line is not

● Neutral color point

● Complementary colors

● Primary hue

CIE Chart

Complementary colors● Opposites

● Enhance one another because of optimal color contrast

Color Gamut● Only a small subset

of possible percievable colors can be reproduced– Fall into convex hull

of primaries● Two primaries results

in a line● Three primaries

results in a triangle

Munsell System● Created in 1905 by

artist A. H. Munsell

● Five hues spaced preceptually equal– Purple, Yellow,

Green, Blue, Purple

– Saturation

– Value

RGB System● RGB Color model

uses three primaries– Red

– Green

– Blue

● Colors are in the interior of cube

RGB Color Space

Macbeth Color Chart● Grayscale

– Light to dark

● Colors– Designed to match

reflectance of natural objects

Subtractive Color Mixing● Uses reflected light● Some is absorbed● Some is reflected● Three primaries

– Red (Magenta)– Yellow– Blue (Cyan)

Subtractive Color Mixing● Du Hauron

– 1869– Les Couleours en

Photographie

Additive Color Mixing● Uses emitted light or

light transmitted through a filter

● Three primaries– Red (Vermillion)– Green– Blue (Royal)

Additive Color Mixing● 3 Flashlights

Hue, Saturation, Value

Hue, Lightness, Saturation● Similar to HSV and

RGB models