The Visual System and Visual Performance School of Mechanical, Industrial, and Manufacturing Engineering
Photometry: Electromagnetic Spectrum School of Mechanical, Industrial, 2 and Manufacturing Engineering
Photometry: Basic Concepts Source Luminous flux - lumens Observer Luminance - foot-lamberts Illuminance - milli-Lamberts - lux - nits (cd/m 2 ) - foot-candles Reflective surface School of Mechanical, Industrial, 3 and Manufacturing Engineering
Photometry: Concepts and Units Luminous intensity Luminance ● ● Luminous power / unit solid angle Luminous flux leaving ● ● SI units: candelae/candelas (cd) (reflected from) a surface ● Candle emits ~1cd Units ● ● Luminous flux SI: cd / m 2 = “nits” – ● Non-SI: footlamberts(fL) Power of light perceived by – ● = lm / ft 2 human eye (visible light) Contrast: luminance ratio vs radiant flux (total power) ● ● SI units: lumens (lm) Reflectance: % reflected ● ● 1 lm = 1 cd∙sr Brightness: perception ● ● Illuminance ● Luminous flux reaching a surface ● per unit area Units ● SI: lux (lx) = lm / m 2 – 1 steradian (sr) Non-SI: footcandles (fc) = lm / ft 2 – Source: Wikimedia commons, http://upload.wikimedia.org/wikipedia/commons/thu mb/9/98/Steradian.svg/200px-Steradian.svg.png School of Mechanical, Industrial, 4 and Manufacturing Engineering
Luminance Luminance, Example milliLamberts (mL) 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. School of Mechanical, Industrial, 5 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 School of Mechanical, Industrial, 6 and Manufacturing Engineering
The CIE Color System (Commission Internationel de L'Elairage : International Commission on Illumination ) System, developed in 1931, to specify ● . 4 colors 2 2 , y g Based on experiments conducted in e n ● l p i W . 1 1920s 3 : k 9 r 1 o y Y Idea: any color specified by x w ● E e I C N combination of 3 primaries, e.g., red, : e , l g i F n green, blue (RGB) / i i r k e i e w n / x & y axes represent proportions of two g i g ● r o n E . a “imaginary” colors, “red” (r) and “green” i s d m e p e (g), which determine remaining i t k s i y w S . proportion of “blue” (b): n n e I / / s : p r o r t t t h c x = a , s F n r + g + b n o a m m m u o H g C . ) y = a 6 i 9 d r + g + b e 9 1 m ( i k . A i W , s : i s n e a c p r a u h o C s School of Mechanical, Industrial, 7 and Manufacturing Engineering
The CIE Color System (Commission Internationel de L'Elairage : International Commission on Illumination ) System, developed in 1931, to specify ● . 4 colors 2 2 , y g Based on experiments conducted in e n ● l p i W . 1 1920s 3 : k 9 r 1 o y Y Idea: any color specified by x w ● E e I C N combination of 3 primaries, e.g., red, : e , l g i F n green, blue (RGB) / i i r k e i e w n / x & y axes represent proportions of two g i g ● r o n E . a “imaginary” colors, “red” (r) and “green” i s d m e p e (g), which determine remaining i t k s i y w S . proportion of “blue” (b): n n e I / / s : p r o r t t t h c x = a , s F n r + g + b n o a m m m u o H g C . ) y = a 6 i 9 d r + g + b e 9 1 m ( i k . A i W , s : ● “Safety” colors indicated i s n e a c p r a u h o C s School of Mechanical, Industrial, 8 and Manufacturing Engineering
Munsell Color System ● Developed in early 1900s ● Early use was for soil research ● Specifies color in terms of ● Lightness/Value ● Hue (“color”) ● Saturation/Chroma source: Wikimedia Commons, http://en.wikipedia.org/wiki/File:Munsell-system.svg School of Mechanical, Industrial, 9 and Manufacturing Engineering
Federal Standard 595C - Colors Used in Government Procurement FED-STD-595 ● Color description & Reds communication system ● Developed 1956 by US government ● Means of specifying colors to contractors, vendors ● Federal Standard 595 Oranges Color Server: http://www.colorserver.net/ School of Mechanical, Industrial, 10 and Manufacturing Engineering
Anatomy and Physiology: The Eye Illustration by Mark Ericksen, St. Luke’s Cataract and Laser Center, StLukesEye.com School of Mechanical, Industrial, 11 and Manufacturing Engineering
Anatomy and Physiology: The Eye (2) Sclera: white of the eye, fibrous, Vitreous Humor (lens-retina chamber) ● ● protective Shape ● Iris Choroid: vascular layer, connective ● ● tissue between sclera and retina Light control ● Focusing Optic Nerve ● ● Cornea Nerve signals to brain ● ● Protection Optic Disk: blind spot ● ● Focusing Retina ● ● Pupil: opening Rods: black & white, night vision ● ● Lens Cones: color, day vision ● ● Macula: area of greater acuity Focusing (ciliary muscles) ● ● Fovea: greatest actuity (highest Accommodation ● ● concentration of cones) Conjunctiva: clear, covers sclera, lines ● Eye Muscles eyelids ● Eye movement Aqueous Humor (cornea-lens ● ● Convergence chamber) ● Shape ● Nutrition ● School of Mechanical, Industrial, 12 and Manufacturing Engineering
Rod and Cone Cells Rods Cones Location periphery macula/fovea Acuity - (lower density) + (higher density) Sensitivity + (scotopia) - (photopia) Color - + Adaptation rapidly lose sensitivity little affected by intensity Wavelengths sensed insensitive to red School of Mechanical, Industrial, 13 and Manufacturing Engineering
Visual Performance ● Brightness ● Visual Angle ● Visual Acuity ● Color ● Visual Field School of Mechanical, Industrial, 14 and Manufacturing Engineering
Brightness ● Relative amount of light reflected from an object produces a sensation of lightness or brightness. ● Brightness is related to the luminance of light as well as a subjective response to color School of Mechanical, Industrial, 15 and Manufacturing Engineering
Visual Angle (VA) S VA = 2 arctan (S/2D) Object VA D Viewer Eyepoint School of Mechanical, Industrial, 16 and Manufacturing Engineering
Visual Angle (VA) S VA = 2 arctan (S/2D) Object Object VA (degrees) Quarter at arms length 2.3 Quarter at 10 ft 0.5 Toyota Corolla at 100 yd 2.9 VA 100 ft Douglas Fir @ 300 yd 6.4 D Viewer Eyepoint School of Mechanical, Industrial, 17 and Manufacturing Engineering
Visual Angle (VA) S VA = 2 arctan (S/2D) Object Object VA (degrees) Quarter at arms length 2.3 Quarter at 10 ft 0.5 VA Toyota Corolla at 100 yd 2.9 D 100 ft Douglas Fir @ 300 yd 6.4 Mt Jefferson at 72 mi (H) 0.4 Mt Jefferson at 72 mi (W) 1.6 Cell Tower Pole at 300 yd (dia) 0.3 Cell Tower Antennae at 300 yd (H) 3.9 180 ft Cell Tower at 300 yd (H) 11.4 Viewer Eyepoint School of Mechanical, Industrial, 18 and Manufacturing Engineering
Mt. Jefferson/Cell Tower Comparison NB: lower portion of tower clipped by bottom of photo School of Mechanical, Industrial, 19 and Manufacturing Engineering
Mt. Jefferson/Cell Tower Comparison Object VA (degrees) Mt Jefferson at 0.4 72 mi (H) Cell Tower 3.9 Antennae at 300 yd (H) Cell Tower Antennae > 9x Mt Jefferson 180 ft Cell Tower 11.4 at 300 yd (H) 180 ft Cell Tower > 28x Mt Jefferson NB: lower portion of tower clipped by bottom of photo School of Mechanical, Industrial, 20 and Manufacturing Engineering
Cumulative Probability of Detection School of Mechanical, Industrial, 21 and Manufacturing Engineering
Visual Acuity ● Ability to resolve detail ● Often, inverse of smallest visual angle (in minutes) that can be resolved ● e.g., Acuity = 1 ● Observer can resolve/detect a feature of 1 minute VA School of Mechanical, Industrial, 22 and Manufacturing Engineering
Variation in Visual Performance Across the Retina School of Mechanical, Industrial, 23 and Manufacturing Engineering
Minimum Separable Acuity ● Also called gap resolution ● Smallest VA eye can detect between parts of a target (visual object). School of Mechanical, Industrial, 24 and Manufacturing Engineering
Minimum Separable Acuity as Function of Contrast School of Mechanical, Industrial, 25 and Manufacturing Engineering
Minimum Perceptible Acuity ● Also called spot detection. ● Eye’s ability to detect smallest possible target. School of Mechanical, Industrial, 26 and Manufacturing Engineering
Minimum Perceptible Acuity as Function of Contrast and Background Luminance School of Mechanical, Industrial, 27 and Manufacturing Engineering
Vernier Acuity ● Smallest lateral displacement of one line from another that can be detected. School of Mechanical, Industrial, 28 and Manufacturing Engineering
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