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 Every color can be matched by adding three primaries

Hermann Helmholtz German Scientist – Verified Young's theory by identifying three types of receptors in the eye in 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