Chapter 27 Color 29-Apr-18 Physics 1 (Garcia) SJSU

Spectrum of Visible Light 29-Apr-18 Physics 1 (Garcia) SJSU

Wavelengths & Photons Particles of light, called photons, each have a wavelength. Red Photon Yellow Photon Green Photon Blue Photon Prism Spectrum 29-Apr-18 Physics 1 (Garcia) SJSU

Newton’s Color Wheel Prism spectrum is a straight line, so why did Isaac Newton describe color using a circular wheel? 29-Apr-18 Physics 1 (Garcia) SJSU

Not in the spectrum. How do we see these? Additive Color Wheel Not in the spectrum. How do we see these? Spectral Colors R M Y Red Yellow Green Cyan Blue Magenta B G C 29-Apr-18 Physics 1 (Garcia) SJSU

Adding Colored Lights Stream of red & green photons looks same as yellow photons (metamerism) YELLOW Eye to Brain or Notice overlap of red, green, & blue is seen as white light Theatrical lighting 29-Apr-18 Physics 1 (Garcia) SJSU

Demo: Seeing Yellow Sodium lamps emit yellow photons Color monitor can only emit red, green, and blue (RGB); creates other colors by selectively turning RGB pixels on or off. 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic Theorists Thomas Young (1773-1829) English physicist Hermann von Helmholtz (1821-1894) German physicist James Clerk Maxwell (1831-1879) Scottish physicist 29-Apr-18 Physics 1 (Garcia) SJSU

Simple Trichromatic Theory Yellow, Green & Cyan photons excite me Yellow & Red photons excite me Cyan & Blue photons excite me MOE LARRY CURLY Inside your eye there are three receptors 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic: Seeing Yellow Yellow, Green & Cyan photons excite me. I’M EXCITED Yellow & Red photons excite me. I’M EXCITED Cyan & Blue photons excite me. Yawn. CURLY MOE LARRY Yellow seen when Curly and Larry excited, either by yellow photons or red & green photons. 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic: Seeing Magenta Yellow & Red photons excite me. I’M EXCITED Cyan & Blue photons excite me. I’M EXCITED Yellow, Green & Cyan photons excite me. Yawn. CURLY MOE LARRY Magenta is seen by eye when Moe and Larry excited, which no single type of photon can achieve. 29-Apr-18 Physics 1 (Garcia) SJSU

Demo: Maxwell Color Disk Disk painted half red, half blue looks magenta when rapidly spinning. 29-Apr-18 Physics 1 (Garcia) SJSU

Mixing Blue & Red Paint Mixing paint or ink is different from adding colors together by light. Mix of blue and red paint produces a blackish brown 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic: Seeing White Yellow & Red photons excite me. I’M EXCITED Cyan & Blue photons excite me. I’M EXCITED Yellow, Green & Cyan photons excite me. I’M EXCITED CURLY MOE LARRY White seen when all three very excited Gray seen when all three less excited 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic: Color Blindness Red , Yellow, Green & Cyan photons excite me. I’M EXCITED Cyan & Blue photons excite me. Yawn. Color blindness occurs if the eye is missing one of the three receptors. Other receptors try to compensate but cannot distinguish some colors. CURLY MOE LARRY Do I see red or green? 29-Apr-18 Physics 1 (Garcia) SJSU

Color Blindness Weakness or absence of one of the three types of cones is the cause of color blindness, leading to a reduced ability to distinguish colors. Classification Incidence (%) Males Females Anomalous Trichromacy 6.3 0.37 Protanomaly (Red-cone weak) 1.3 0.02 Deuteranomaly (Green-cone weak) 5.0 0.35 Tritanomaly (Blue-cone weak) 0.0001 Dichromacy 2.4 0.03 Protanopia (Red-cone absent) Deuteranopia (Green-cone absent) 1.2 0.01 Tritanopia (Blue-cone absent) 0.001 Rod Monochromacy (no cones) 0.00001 29 or 70? 21 or 74? 29-Apr-18 Physics 1 (Garcia) SJSU

Trichromatic: After-Image First stare at RED I’M EXCITED! Yawn. MOE CURLY LARRY Me too, but tired. ME TOO! I’M EXCITED! MOE CURLY LARRY Then stare at WHITE Moe and Curly are excited so what color is seen? CYAN (light blue-green) 29-Apr-18 Physics 1 (Garcia) SJSU

Negative After-image Stare, unfocused, at the red cross for 10 seconds then look at white wall 29-Apr-18 Physics 1 (Garcia) SJSU

Negative After-image Cyan 29-Apr-18 Physics 1 (Garcia) SJSU

Negative After-image 29-Apr-18 Physics 1 (Garcia) SJSU

Negative After-image Cyan Magenta Yellow 29-Apr-18 Physics 1 (Garcia) SJSU

Simple Additive Color Wheel LARRY Newton’s color wheel is a simple formulation of trichromatic theory. White CURLY MOE 29-Apr-18 Physics 1 (Garcia) SJSU

Color Vision in the Eye Three types of cones (color) One type of rod (B/W only) 29-Apr-18 Physics 1 (Garcia) SJSU

CIE Hue-Saturation Diagram Eye is not a perfect optical instrument. Color “wheel” is actually distorted cone shape. Rim is full saturation, center is white CURLY % 50% Larry 50% Curly 0% Moe 33% Larry 33% Curly 33% Moe 29-Apr-18 Physics 1 (Garcia) SJSU LARRY %

Spectral Reflectance Curves White Red                                                        When white light shines on an object, some photons absorbed, others reflected by the object’s surface. 29-Apr-18 Physics 1 (Garcia) SJSU

Name That Color Dark Brown White Red (Burnt Sienna) 100% 0% 29-Apr-18 BLUE GREEN RED 0% 100% BLUE GREEN RED BLUE GREEN RED Dark Brown (Burnt Sienna) White Red 29-Apr-18 Physics 1 (Garcia) SJSU

Name That Color Bluish Green Bright Yellow Blue (Cobalt) 100% 0% BLUE GREEN RED 0% 100% BLUE GREEN RED BLUE GREEN RED Bluish Green Bright Yellow Blue (Cobalt) 29-Apr-18 Physics 1 (Garcia) SJSU

Subtractive Color Absorbing filters or absorbing pigments remove colors from white light. Check Yourself: Yellow = Red + Green Cyan = Blue + Green Yellow & Cyan filters (or pigments) combine to give … Overlapping color filters 29-Apr-18 Physics 1 (Garcia) SJSU

Check Yourself A soap film absorbs red, green, or blue light, depending on the film’s thickness. What colors do we see where red is removed? Where green is removed? Where blue is removed? 29-Apr-18 Physics 1 (Garcia) SJSU

Four Color Printing Magenta Yellow Cyan Black Magenta + Yellow + Cyan Green balloon printed with mix of yellow and cyan inks Magenta + Yellow + Cyan All Four 29-Apr-18 Physics 1 (Garcia) SJSU

Check Yourself Which inks are mixed for the bright red balloon and dark red dress? Magenta Yellow Cyan Black 29-Apr-18 Physics 1 (Garcia) SJSU