class 02-1 vision

class 02-1 vision - The Visual System and Visual...

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School of Mechanical, Industrial, and Manufacturing Engineering The Visual System and Visual Performance
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2 School of Mechanical, Industrial, and Manufacturing Engineering Photometry: Electromagnetic Spectrum
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3 School of Mechanical, Industrial, and Manufacturing Engineering Photometry: Basic Concepts Source Reflective surface Observer Luminous flux - lumens Illuminance - lux - foot-candles Luminance - foot-lamberts - milli-Lamberts
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4 School of Mechanical, Industrial, and Manufacturing Engineering Photometry: Concepts and Units Luminous intensity Power of light emitted by source in particular direction SI units: candelas (cd) Candle emits ~1cd Luminous flux Power of light perceived by human eye (visible light) vs radiant flux (total power) SI units: lumens (lm) 1 lm = 1 cd∙sr Illuminance Luminous flux reaching a surface per unit area Units SI: lux (lx) = lm / m 2 Non-SI: footcandles (fc) = lm / ft 2 Luminance Luminous flux leaving (reflected from) a surface Units SI: cd / m 2 = “nits” Non-SI: footlamberts(fL) = lm / ft 2 Contrast: luminance ratio Reflectance: % reflected Brightness: perception 1 steradian (sr) Source: Wikimedia commons, http://upload.wikimedia.org/wikipedia/commons/thu mb/9/98/Steradian.svg/200px-Steradian.svg.png
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5 School of Mechanical, Industrial, and Manufacturing Engineering Luminance Luminance, milliLamberts (mL) Example 1,000,000,000 sun's surface at noon 1,000,000 tungsten filament 10,000 white paper in sunlight 1,000 earth on clear day 100 earth on cloudy day 10 white paper in reading light 1 white paper 1 ft from candle 0.001 earth in moonlight 0.0001 white paper in starlight Note: 1 footlambert (ft-L) = 0.929 mL, so 1 ft-L ~ 1 mL.
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6 School of Mechanical, Industrial, and Manufacturing Engineering Luminance (2) Threshold of detectability 1 x 10 -6 mL Threshold of pain 3 x 10 4 mL Limits to discriminability 3 - 4 levels
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7 School of Mechanical, Industrial, and Manufacturing Engineering The CIE Color System (C ommission I nternationel de L'E lairage : International Commission on Illumination ) System, developed in 1931, to specify colors Based on experiments conducted in 1920s Idea: any color specified by combination of 3 primaries, e.g., red, green, blue (RGB) x & y axes represent proportions of two “imaginary” colors, “red” (r) and “green” (g), which determine remaining proportion of “blue” (b): s o u r c e s : W i k i m e d i a C o m m o n s , h t t p : / / e n . w i k i p e d i a . o r g / w i k i / F i l e : C I E x y 1 9 3 1 . p n g C h a p a n i s , A . ( 1 9 9 6 ) . H u m a n F a c t o r s I n S y s t e m s E n g i n e e r i n g , N e w Y o r k : W i l e y , 2 2 4 . x = r r + g + b y = g r + g + b
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8 School of Mechanical, Industrial, and Manufacturing Engineering The CIE Color System (C ommission I nternationel de L'E lairage : International Commission on Illumination ) System, developed in 1931, to specify colors Based on experiments conducted in 1920s Idea: any color specified by combination of 3 primaries, e.g., red, green, blue (RGB) x & y axes represent proportions of two
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