A World of Color Session 5 Colors of Things OLLI at Illinois Spring 2018 D. H. Tracy
Course Outline 1. Overview, History and Spectra 2. Nature and Sources of Light 3. Eyes and Color Vision 4. Color Spaces and Color Mixing 5. Origins of Colors of Things 6. Visual Perception: Neurons and the Brain 7. Color Recording and Reproduction, Media 8. Color in Arts and Culture, Emotive Aspects 2/22/2018 World of Color 5 2
Session 5 Outline Colors of Things Wrap up Color Spaces Amber match redux Luminance and color Color Bucket List Photometry Colors of Things How things get their colors Dyes and Pigments Demo of absorption & reflection Paints Colors in nature 2/22/2018 World of Color 5 3
Color Perception Train Source Brain Optic Nerve Object Medium Eye 2/22/2018 World of Color 5 4
Relative Sensitivity Each Cone Type Registers a Signal S M L S M L λ 2/22/2018 World of Color 5 5
y CIE* 1931 Color Space (x & y Hue Coordinates) Chromaticity Diagram *CIE = International Commission on Illumination (Commission Internationale de l éclairage) 2/22/2018 World of Color 5 6 x
Metamers CIE 1931 xy Color Space Chromaticity Diagram Thousands or Millions of Metamers in this case In a sense we are all profoundly color blind we can t distinguish any of them! 2/22/2018 World of Color 5 7
Analysis of the Amber Matching Demo [Last Week] CIE 1931 xy Color Space Chromaticity Diagram Green LED Amber LED (Reference) Red LED 2/22/2018 World of Color 5 8
Analysis of the Amber Matching Demo [Improved] CIE 1931 xy Color Space Chromaticity Diagram Green LED Reference LED Adjusted Reference Red LED Blue LED 2/22/2018 World of Color 5 9
Demo of Color Matching (Improved) Ref Variable 2/22/2018 World of Color 5 10
CIE 1931 xy Color Space y 2/22/2018 World of Color 5 x 11
We ignored Luminance Thinking it had no effect on color 2/22/2018 World of Color 5 12
Dark Adaptation 2/22/2018 World of Color 5 13
2/22/2018 World of Color 5 14
Meanwhile, out West. 2/22/2018 World of Color 5 15
2/22/2018 World of Color 5 16
2/22/2018 World of Color 5 17
2/22/2018 World of Color 5 18
2/22/2018 World of Color 5 19
Luminance Matters 100% 50% 2/22/2018 World of Color 5 20
Luminance Matters 100% 50% 2/22/2018 World of Color 5 21
Luminance doesn t change all hues so much 100% 50% 2/22/2018 World of Color 5 22
Others a bit more Yellow R + G 100% 50% Cyan G + B Magneta B + R 2/22/2018 World of Color 5 23
Novel Color? 2/22/2018 World of Color 5 24
Computer Display Gamuts CIE 1931 xy Color Space srgb Gamut 2/22/2018 World of Color 5 25
Microsoft Office Color Specification 2/22/2018 World of Color 5 26
Microsoft Office Color Model Saturation Hues in Spectral Order RGB Color Space Alternate to RGB: HSL (Hue, Saturation, Lightness) 2/22/2018 World of Color 5 27
Microsoft Office Color Model Saturation Hues in Spectral Order RGB Color Space srgb Gamut Alternate to RGB: HSL (Hue, Saturation, Lightness) 2/22/2018 World of Color 5 28
Gamut of Common Reflected Colors: Pointer s Gamut (Michael J Pointer, 1980) Measured Reflected Light from 4089 everyday objects (man made & natural) -non-fluorescent BUT- There are common emitting sources of higher saturation: LEDs Neon Lights Lasers Fireworks 2/22/2018 World of Color 5 29
Your Color Bucket List^ Pointer s Gamut srgb Daylight Pointer s Gamut srbg^ Blackbodies^ BB These you ve always seen. 2/22/2018 World of Color 5 30
Your Color Bucket List^ Pointer s Gamut srgb Daylight Pointer s Gamut srbg^ Blackbodies^ Lasers and LEDs^ Full Spectrum^ Outer Zone BB We ll look at these as well [Outer zone by mixing spectral colors with white] 2/22/2018 World of Color 5 31
Bucket List: 1. Lasers 2. LEDs 3. Monochromatic Spectral Colors 4. Outer Zone (add White) 2/22/2018 World of Color 5 32
Your Color Bucket List Missing colors: Purples Pointer s Gamut srgb Daylight Pointer s Gamut srbg^ Blackbodies^ Lasers and LEDs^ Full Spectrum^ Outer Zone ^ Purple Line^ BB 2/22/2018 World of Color 5 33
New Color: OLLI Purple Device mixes 402nm laser + 630nm LED Diffuser is frosted aluminum foil For people with artificial lenses, 402nm is very bright 2/22/2018 World of Color 5 34
Photometry and Colorimetry: Measuring Human Color Perception Essential idea: Ask observer to compare two patches of light Are they distinguishable? Essential Tool: Monochromator Isolates single wavelength Side Flicker by Side Monochromator Flicker λ 500 B 10 (microwatts) (nanometers) 2/22/2018 World of Color 5 35
How Can We Measure Spectral Luminosity Curve? 2/22/2018 World of Color 5 36
Determine Eye Spectral Luminosity Curve Monochromator Monochromator Reference Light: Stays fixed λ 500 B 10 λ 650 B 10 Variable Light Are the patches equal in brightness? No. I ll turn up the intensity 2/22/2018 World of Color 5 37
Observer Adjusts Brightness of Second Light Monochromator Monochromator Reference Light: Stays fixed λ 500 B 10 λ 650 B 190 Variable Light Now are the patches equal in brightness? Well, maybe. I can t tell. It s Pears and Apples! How can we sidestep this problem? One way is to use Rod vision (Scotopic) 2/22/2018 World of Color 5 38
Filters reduce intensity 10,000x Observer Dark Adapts for 1 hour Reference Light: Stays fixed Monochromator λ 500 B 10 Monochromator λ 650 B 200 190 Variable Light Neutral Density Filter (0.01% T) 2/22/2018 World of Color 5 39
Filters reduce intensity 10,000x Observer Dark Adapts for 1 hour Reference Light: Stays fixed Monochromator λ 500 B 10 Monochromator λ 650 B 190 Variable Light Neutral Density Filter (0.01% T) What your rods see 2/22/2018 World of Color 5 40
Filters reduce intensity 10,000x Observer Dark Adapts for 1 hour Reference Light: Stays fixed Monochromator λ 500 B 10 Monochromator λ 650 B 190 Variable Light Neutral Density Filter (0.01% T) Do the patches match? No, the variable is a little too dim. I ll turn it up to 200 μwatts. 2/22/2018 World of Color 5 41
Filters reduce intensity 10,000x Observer Dark Adapts for 1 hour Reference Light: Stays fixed Monochromator λ 500 B 10 Monochromator λ 650 B 200 190 Variable Light Neutral Density Filter (0.01% T) Now are the patches equal in brightness? No, the variable is a little too dim. I ll Yes, turn they it up match! to 200 μwatts. 2/22/2018 World of Color 5 42
Filters reduce intensity 10,000x Observer Dark Adapts for 1 hour Reference Light: Stays fixed Neutral Density Filter (0.01% T) Monochromator λ 500 B 10 Monochromator λ 650 B 200 190 Variable Light Conclusion: Since it took 200μW of red 650nm light to match just 10μW of cyan 500nm light Our Rods must be only 1/20 th (5%) as sensitive at 650nm as at 500nm Now are the patches equal in brightness? No, the variable is a little too dim. I ll Yes, turn they it up match! to 200 μwatts. 2/22/2018 World of Color 5 43
And That s How We Measure the Scotopic Standard Luminosity Curve Rods 2/22/2018 World of Color 5 44
And That s How We Measure the Scotopic Standard Luminosity Curve Rods Red Light OK [does not affect rods or dark adaptation] 2/22/2018 World of Color 5 45
How Can We Obtain the Photopic Curve? Answer: The Flicker Photometer Reference Light: Stays fixed Monochromator λ 550 B 10 Monochromator λ 650 B 190 Variable Light Chopper Wheel Alternates Colors Can you see any Color Flicker?^ Yes. Red alternates with green. Better speed up the chopper. 2/22/2018 World of Color 5 46
How Can We Obtain the Photopic Curve? Answer: The Flicker Photometer Reference Light: Stays fixed Monochromator λ 550 B 10 Monochromator λ 650 B 190 Variable Light Chopper Wheel Alternates Colors Can you see any Flicker? Flicker ~ 20 Hz Yes, intensity flickers rapidly. I ll adjust the Variable Intensity.^ 2/22/2018 World of Color 5 47
How Can We Obtain the Photopic Curve? Answer: The Flicker Photometer Reference Light: Stays fixed Chopper Wheel Alternates Colors Monochromator λ 550 B 10 Monochromator λ 650 B 190 100 Variable Light Conclusion: Since it took 100μW of red 650nm light to match 10μW of green 550nm light Our Photopic eye must be only 1/10 th (10%) as sensitive at 650nm as at 550nm Flicker ~ 20 Hz Now can you see any Flicker? No. We have a Luminosity Match.^ 2/22/2018 World of Color 5 48
And That s How We Measure the Photopic Standard Luminosity Curve Rods All 3 Cones Together 2/22/2018 World of Color 5 49
Colors of Objects 2/22/2018 World of Color 5 50
Color Perception Train Source Brain Optic Nerve Object Medium Eye 2/22/2018 World of Color 5 51
Object Coloration: Themes Color depends on illumination spectrum^ Color affected by Photon interactions with object: ^ Absorption Redirection Fluorescence λ IN λ OUT 2/22/2018 World of Color 5 52
Object Coloration: Themes Color depends on illumination spectrum^ Color affected by Photon interactions with object: ^ Absorption Redirection Fluorescence λ IN λ OUT Scattering Plays a Large Role 2/22/2018 World of Color 5 53
Absorption vs. Redirection Absorption Chromophores Dyes Pigments Redirection Refraction (with Dispersion) Interference 1Photon annihilation 2Atom, molecule etc. excited 3 Energy usually converted to heat Diffraction Scatter 2/22/2018 World of Color 5 54
Organic Dyes Absorbing Chromophores Beta-Carotene Indigo Mauveine First synthetic dye (analine) 1856 William Henry Perkin, age 18 Brilliant Blue FCF (Blue #1) 2/22/2018 World of Color 5 55
Carmine Dye Highly Saturated Red Carminic Acid Alum Cochineal K Al (SO 4 ) 2 12 H 2 O Carmine Lake 2/22/2018 World of Color 5 56
Carmine Dye Highly Saturated Red Natural Red #4? Artificial Crab Red candies, soft drinks, yogurts, popsicles, cosmetics etc. 2/22/2018 World of Color 5 57
Absorbance % Transmission Transmission vs Absorption Spectra Red Fabric Dye Low T When Transmission is < 100%, Photon Absorption is happening Absorbance is the flip side of Transmission High Abs 2/22/2018 World of Color 5 58
Metallic Ions Example: More Absorbing Chromophores Dilute Ions in Aluminum Oxide (Alumina) Al 2 O 3 (Corundum) Ruby Cr +3 (1%) Iron+Titanium -> Blue Chromium -> Pink or Red Copper -> Orange Magnesium -> Green Sapphire Ti +4 & Fe +2 (.01%) 2/22/2018 World of Color 5 59
Metals in Glass Usually various metal ions or compounds Sometimes scattering by metal nano-particles 2/22/2018 World of Color 5 60
Gold Nanoparticles Scatter and Absorb via Plasmon Resonances Science of Stained Glass, UW Madison MRSEC 2/22/2018 World of Color 5 61
Color of Things Demo 2/22/2018 World of Color 5 62
Metallic Reflection 2/22/2018 World of Color 5 63 Anish Kapoor, Cloud Gate, Millennium Park
Specular Reflection Polished Metal Obeys Law of Reflection, but absorbs some photons (Aluminum) (Gold) If the surface is rough, we get Diffuse The Reflection Electromagnetic Wave penetrates a short distance into the metal! (Silver) 2/22/2018 World of Color 5 64
Pigments: Solid Particles in Suspension 2/22/2018 World of Color 5 65
Pigment Particles Scatter and Absorb Photons Red & Green photons absorbed by pigment Mixed Pigments 2/22/2018 World of Color 5 66
Examples of Common Inorganic Pigments www.compoundchem.com 2/22/2018 World of Color 5 67