eee508_HVSColorModels

eee508_HVSColorModels - Vision & Perception so e cept o...

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Vision & Perception Simple model: ¾ simple reflectance/illumination model Eye illumination source i ( n 1 , n 2 ) ¾ image: x ( n 1 , n 2 )= i ( n 1 , n 2 ) r ( n 1 , n 2 ) reflectance term r ( n 1 , n 2 ) where 0 < i ( n 1 , n 2 ) < f 0 < r ( n 1 , n 2 ) < 1 EEE 508
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Vision & Perception Imaging on the retina (back of eye consisting of photoreceptors) Focal point of lens Eye 2m Retinal image 17mm 20mm 100m EEE 508
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Vision & Perception Visible range of electromagnetic spectrum is 350 nm to 780 nm. O 380nm 780nm J rays x rays ultraviolet visible infrared microwaves radio EEE 508
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Vision & Perception Simple model for HVS eye brain optic nerve HVS HVS Input (spatial pulse) What we see Output What we think we see Approximate HVS with a LTI system ¾ NOTE: The HVS is really a non-linear system. Primarily a BPF/LPF EEE 508 NOTE: The HVS is really a non linear system.
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Vision & Perception Light: electromagnetic radiation that stimulates our visual response ¾ expressed as a spectral energy distribution C ( O ); 380nm d O d 780nm – wavelength in visible spectrum Spectral distribution of a colored light C ( ) represents amount of energy present at each frequency wavelength EEE 508
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Vision & Perception Color vision model (3 receptor absorption model) ¾ 3 types of cones: each has a different peak absorption frequency Typical absorption spectra (also called sensitivity curves) for the three cones (not to scale EEE 508 (not to scale)
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Vision & Perception Let C ( O ): spectral energy distribution of a “colored” light source C ( ) max max min EEE 508
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Vision & Perception Color sensation described by ±² >@ ±²±² 3 , 2 , 1 , max min ³ i d C S C i i O D ¾ i [ C ( )], i=1,2,3 , called spectral responses ¾ If C 1 ( ) and C 2 ( ) produce responses such that i [ C 1 ( )]= i [ C 2 ( )] for i = 1,2,3 ´ C 1 ( ) and C 2 ( ) perceived to be identical Color sensation – perceptual attributes 1. Brightness – perceived Luminance 2. Hue – color 3. Saturation – amount of white light diluting the color EEE 508
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Vision & Perception The following curves show the relative spectral response functions of each of the 3 types of cones: 0.2 R G bed B on of light absor ch type of cone 400 700 550 O (nm) 0 0.01 Fracti by eac ¾ Eye’s response to Blue light is much less strong than is its response to Red or Green EEE 508
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Vision & Perception Luminance and Brightness ¾ The luminance or intensity of an object with light spectral distribution I ( x , y , O ) is f d V L where V ( ) is the “relative luminous efficiency function” of the HVS Bel shaped curve = sum of 3 previous curves ± ² ± ² ³ 0 ) , , ( , y x I y x Bell-shaped curve = sum of 3 previous curves. EEE 508
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Vision & Perception Luminance versus Brightness ¾ Brightness: 9 subjective perceptual measure (depends on observer’s judgment) 9 perceived Luminance 9 depends on luminance of the surround (lateral inhibition, contrast) ¾ Luminance: 9 objective quantitative measure (Unit: watts/m 2 or watts/steradians) 9 id d t fth l i fth d i b j t independent of the luminances of the surrounding objects Note: the illumination (Luminance) range over which HVS can operate is roughly 10 10 (normalized unit, e.g. milli-luminance = milli-unit of luminance) or 10 orders of magnitude on log scale.
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This document was uploaded on 03/11/2012.

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eee508_HVSColorModels - Vision &amp; Perception so e cept o...

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