Importance of Color Painters first used charcoal Early artists used ochre to add red Colors are not...

Importance of Color

• Painters first used charcoal

• Early artists used ochre to add red

• Colors are not always the same from culture to culture

Blackbody Radiators

• A theoretical model of how objects emit radiation based on temperature

• Examples– Incandescent light 2854K– Direct sunlight 4874K

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

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 discrimination of blues

Color Blindness

• Tritanopia– No blue cones

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

Color Gamut

• Only a small subset of possible perceivable colors can be reproduced– Fall into convex hull of

primaries• Two primaries results in a

line• Three primaries results in

a triangle

RGB Color Model

• Additive colors• Three primaries– Red– Green– Blue

• Roughly match the sensitivities of cones

• Used in digital images• Used in emissive color

displays

CYMK Color Model

• Subtractive color model– Starts with white– Reduces reflected light

• Three primaries– Cyan– Yellow– Magenta

• Black (key) is used to reduce brightness without changing the hue

CYMK Color Model

Complementary colors

• Opposites• Enhance one another

because of optimal color contrast