18_nature1

18_nature1 - UCSD: Physics 8; 2008 Natural Light The...

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UCSD: Physics 8; 2008 1 Natural Light Natural Light The Physiology of Color The Physiology of Color The Natural Appearance of Things The Natural Appearance of Things
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UCSD: Physics 8; 2008 2 Linear spectrum vs. color Linear spectrum vs. color wheel wheel The spectrum spanning blue to red wavelengths has The spectrum spanning blue to red wavelengths has been shown as a line: red to violet ROYGBIV been shown as a line: red to violet ROYGBIV But we can draw a color wheel But we can draw a color wheel —what’s up w/ that? —what’s up w/ that? Magenta is not in spectrum but from mix of blue and red ends of spectrum
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UCSD: Physics 8; 2008 3 BLUE
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UCSD: Physics 8; 2008 5 Color wheel physiology Color wheel physiology Color wheel is purely a physiological phenomenon Color wheel is purely a physiological phenomenon receptors in our eyes are cyclic in nature red / green receptor and blue / yellow receptor best experienced via afterimages – fatigue of receptors Opponent color scheme Ewald Hering 1874 Opponent color scheme Ewald Hering 1874 Red / green receptor fires more for green , less for red red light inhibits the red / green receptor, while green light stimulates receptor. Nicely accounts for afterimage phenomenon, but . . Color perception is also trichromatic, with separate Color perception is also trichromatic, with separate red red , , green green , and , and blue blue cone receptors cone receptors People choose different colors as “pure green”: A given color has different meaning for different people
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UCSD: Physics 8; 2008 7
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UCSD: Physics 8; 2008 8
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UCSD: Physics 8; 2008 11 Cones in Retina Detect Color Cones in Retina Detect Color QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. With adaptive optics, Austin Roorda and David Williams (1999) were able to determine the packing arrangement of all three cone classes for the first time in the human retina. Figure shows the cone arrangements for two color normal subjects. These are pseudocolor images in which we have falsely colored the cones to be blue, green, or red in order to represent which photoreceptors are S, M, and L cones, respectively. All three cone classes were randomly distributed in both subjects. In addition, the relative number of L- and M-cones differs greatly between these two subjects. The subject on the left has a L to M cone ratio of 3.79 while the subject on the right possesses a L to M ratio of 1.15, yet both subjects possess normal and similar color vision. QuickTim TIFF (Uncompress
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UCSD: Physics 8; 2008 12 Opponent Color Receptor Theory Opponent Color Receptor Theory
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UCSD: Physics 8; 2008 13 After Images caused by neuronal processing in retina After Images caused by neuronal processing in retina The L cone fires more on red and less on green It encodes +R-G When stare at red for 30 seconds, the L cones (most
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This note was uploaded on 04/10/2008 for the course PHYS 8 taught by Professor Tytler during the Spring '08 term at UCSD.

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18_nature1 - UCSD: Physics 8; 2008 Natural Light The...

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