Physics of Color

Mixing Colored Light the lower-frequency red end The frequencies of white light can be divided into three regions: the lower-frequency red end the middle-frequency green part the higher-frequency blue end Low and middle frequencies combine to form yellow to the human eye. The middle and high frequencies appear greenish blue (cyan). The low and high frequencies appear bluish red (magenta).

Mixing Colored Light The low-frequency, middle-frequency, and high-frequency parts of white light appear red, green, and blue. To the human eye, red + green = yellow; red + blue = magenta; green + blue = cyan.

Mixing Colored Light This amazing phenomenon is due to the way the human eye works. The three colors do not have to be red, green, and blue, although those three produce the highest number of different colors. For this reason, red, green, and blue are called the additive primary colors.

Spectrum of Visible Light

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 called Cones

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 OR MOE LARRY Yellow seen when Curly and Larry excited, either by yellow photons or red & green photons.

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.

Maxwell Color Disk Disk painted half red, half blue looks magenta when rapidly spinning.

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

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 OR MOE LARRY Do I see red or green?

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 21 or 74? 29 or 70? Those with a red/green deficiency will see a 21 Those red/green deficient will see a 70

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)

Negative After-image Stare, unfocused, at the red cross for 10 seconds

Negative After-image Cyan

Negative After-image Stare, unfocused, at the flag for 10 seconds

Negative After-image Cyan Magenta Yellow

Additive Complements LARRY After-image of red is cyan because Larry gets tired so when white light excites all three Stooges, Moe & Curly stronger than Larry. R MOE CURLY C Cyan = White - Red

Trichromatic: Opponency Yellow, Green & Cyan photons excite me. I’M EXCITED Yellow & Red photons excite me. I’M EXCITED Oh, Shut The F*@% Up! CURLY MOE LARRY Shine Red & Green photons (or Yellow photons) Yellow seen when Curly and Larry excited, which can annoy Moe, who then opposes them.

Simultaneous Contrast Does the gray bar look slightly bluish? Are the two gray bars the same shade of gray? Yes, the presence of a nearby color affects perception of both hue and value, shifting both towards complement