Precautions for TAs Take control of the projector fan –Turn on the fan – don’t let students do this! –Turn off the fan only after the projectors cooled down. Announce that students: –should not control the fan at all –should dim projectors when not in use

Lab 14: Additive Color Mixing 1.Hue, Brightness (  intensity), Saturation (% white) 2.Calibration of Light Meters 3.White 4.Chromaticity Diagram or Color Triangle 5.Locating R, G, B on the Color Triangle 6.Adding Two Primaries: Blue and Green 7.Red Added to Green; Red Added to Blue 8.Complementary Hues 9.Color Matching 10.Matching Pigments 11.Spectral Colors – The Need for “Negative Intensities” 12.Are There Other Additive Primaries?

Caution keep the fan running all the time. –light bulb (500W) needs a continuous cooling dim/brighten slowly dim the projector when not in use

White Light Newton's dispersion experiment White light Color light

Real Spectrum UVIR = 570 nm (yellow) Light = Electromagnetic wave (nm) nm = m White light  a mixture of infinitely many wavelengths

Over-simplified Spectrum BGR Type IType IIType III Sensitivity (arb. units) Sensitivity of cone cells  RGB primaries Additive primary colors: Red, Green and Blue

Color Triangle Any colors in the color triangle can be obtained by adding (i.e. overlapping light) RGB primaries fraction of red (r) fraction of green (g)

Color Triangle Fraction of red and green in the mixture determines the location of a mixed color fraction of red (r) fraction of green (g) (r, g) = (2/3, 1/3)

Adding R, G, and B Example: S = 100R + 50G + 0B Notation: S = aR + bG + cB 1.Total intensity of light I = (a + b + c) = ( ) = 150 units 2.Fraction of each color r = g = b = Note: sum of fractions  r + g + b = 1

fraction of red (r) fraction of green (g) 100R + 50G r = 0.667, g = 0.333, b = 0 r = g = Orange

Adding R, G, B Example: S = 255R + 0G + 128B 1.total intensity of light I = (R + G + B) = ( ) = 383 units 2.fraction of each color r = g = b =

fraction of red (r) fraction of green (g) 255R + 128B r = 0.67, g = 0, b = 0.33 r = g = 0 Reddish Magenta

fraction of red (r) fraction of green (g) Mixed color lies on the line connecting two colors Mixing two colors Color Triangle Rule Fraction of colors  exact position

fraction of red (r) fraction of green (g) Any colors on a straight line from W: Same hue but increasing saturation Same Hue - Different Saturation Note: Purity = Saturation

fraction of red (r) fraction of green (g) Orange and Brown W and Gray R and less intense R Same Hue - Different Intensity Same (r, g)  Same location

Area of Human Color Vision Spectral colors lie along the edge of the horse shoe shape, outside of color triangle

fraction of red (r) fraction of green (g) W Y SY Complementary Colors SB Complementary color: SB & Y – equidistant from W Complementary hue: B & Y

References Image of dispersion by prism, (1994)

Color Triangle fraction of red (r) fraction of green (g)