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 sunlight 4874K

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 – ● 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 ● 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