Post on 02-Jan-2016
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
Hermann Helmholtz
• German Scientist– 1821-1894
• Verified Young's theory by identifying three types of receptors in the eye in 1852-3
• Invented opthalmoscope
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
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
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