Color perception Color perception Wrong representation sensibility wavelength

Color perception

Wrong representation

sensibility wavelength

Complementary colors

Wrong representation

Color Models : Color Spaces HLS : Hue, Lightness, Saturation Primary wavelength Perceived luminance Purity or vividness

Color Components (cont. ) • Lightness 2/24/99 • Saturation 12

Compute Complementary colors • • Color = (R, G, B) Complementary(color) = ( 1 - R, 1 - G, 1 - B) Adjust brightness an saturation http: //www. colorjack. com/sphere/

sensibility energy wavelength

Color Models : Color Perception C alone cannot be constructed as the superpositions of POSITIVE amounts of the THREE primary colors (r, g, b)

Color Models : Color Perception

Color Sensitivity & Image Detection • Most sensitive to the center of the spectrum – blues & reds must be brighter than greens & yellows • Brightness determined mainly by R+G – expressed on a scale of luminance • light energy corrected for wavelength sensitivity • Shapes detected by finding edges – combine brightness & color differences for sharpness • Implications? – hard to deal w/ blue edges & blue shapes 2/24/99 17

Color Sensitivity (cont. ) • As we age – lens yellows & absorbs shorter wavelengths • sensitivity to blue is even more reduced – fluid between lens and retina absorbs more light • perceive a lower level of brightness • Implications? – don’t rely on blue/black differences for text or small objects! 2/24/99 20

Focus • Different wavelengths of light focused at different distances behind eye’s lens – need for constant refocusing (causes fatigue) – careful about color combinations • Red objects appear closer than blue objects • Pure (saturated) colors require more focusing then less pure (desaturated) 2/24/99 21

Color Guidelines • Use harmonies of Complementary colors • Avoid simultaneous display of highly saturated, spectrally extreme colors – e. g. , no cyans/blues at the same time as reds, why? • refocusing! – desaturated combinations are better pastels 2/24/99 22

Summary • Color can be very helpful, but • Pay attention to – how colors combine – Borders and contrast • Be sensitive to people with limitations – people with color deficiency – color blindness, near/far sighted, and focusing speed 2/24/99 23