Light and Colors CS 148: Summer 2016 Introduction of Graphics and Imaging Zahid Hossain http://lighthouse8.com/wp-content/uploads/2012/08/true-colors.jpg
What is Light ? http://en.wikipedia.org/wiki/Electromagnetic_radiation 2 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
What is Light ? Electric field Magnetic field http://en.wikipedia.org/wiki/Electromagnetic_radiation 3 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
What is Light ? http://en.wikipedia.org/wiki/File:EM_spectrum.svg 4 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Important Facts C = 299,792,458 m/s ( In Vacuum ) Material Speed (multiple of c ) Air 0.9997 Water 0.75 Fused quartz 0.686 Crown glass 0.658 Dense flint glass 0.60 Diamond 0.41 http://wiki.answers.com/Q/What_is_the_velocity_of_light_in_space_and_in_different_materials 5 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Important Facts C = 299,792,458 m/s ( In Vacuum ) Material Speed (multiple of c ) Air 0.9997 Water 0.75 Fused quartz 0.686 Crown glass 0.658 Dense flint glass 0.60 Diamond 0.41 Explains refraction ! & total internal reflection http://wiki.answers.com/Q/What_is_the_velocity_of_light_in_space_and_in_different_materials 6 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Refraction Refractive Index Snell’s Law http://upload.wikimedia.org/wikipedia/commons/1/13/F%C3%A9nyt%C3%B6r%C3%A9s.jpg 7 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Total Internal Reflection When Light travels from denser medium to a lighter medium, the incident angle above a critical angle may cause when: 8 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Wave Particle Duality 9 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Wave Particle Duality 10 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
What have we lost ? • Diffraction • Polarization • Interference 11 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Photon [foh-ton]: A quantum of light that has a position, a direction of propagation, and a wavelength. 12 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Energy Carried by a Photon Speed of Light ~ 3 x 10 8 m/s Frequency (Hz) Planck Constant: 6.63 x 10 -34 J.s Wavelength (m) 13 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Spectral Power Distribution Intuitively: Photons for each wavelength can be counted to give a histogram http://www.lamptech.co.uk/Images/Illustrations/SO%20SPD%27s.jpg 14 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Colors 15 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Types of Cones http://web.stanford.edu/group/vista/cgi-bin/FOV/wp-content/uploads/2012/02/rec.spec_.sens_.png 16 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Measuring Light Perception Sensitivity “This cone sees green light” 17 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Measuring Light Perception Power distribution Sensitivity “This light is orange.” “This cone sees green light” 18 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Measuring Light Perception Multiply and integrate 19 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Measuring Light Perception Multiply and integrate 20 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Cone Responses Power distribution 21 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Cone Responses Sensitivity 22 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Cone Responses Tristimulus values 23 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Conclusion There is an infinite number of wavelengths, but we only see three integral values. 24 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Conclusion There is an infinite number of wavelengths, but we only see three integral values. 25 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Metamers [met-uh-mers] Spectral compositions that create the same tristimulus values. 26 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Implication for Displays We can simulate visual effects of any wavelength by stimulating cones independently. 27 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE Primaries • Red: 700 nm • Green: 546.1nm • Blue: 435.8 nm 28 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Color Matching Experiments 435.8 nm 546.1 nm 700 nm “Match this color.” One wavelength 29 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE RGB Color Matching Spectral Tristimulus Values http://en.wikipedia.org/wiki/CIE_1931_color_space 30 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE RGB Tristimulus Values 31 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE RGB Color Matching http://en.wikipedia.org/wiki/CIE_1931_color_space 32 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Color Matching Experiments 435.8 nm 546.1 nm 700 nm “Match this color.” One wavelength How do you do “Negative Light” ? 33 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE XYZ http://upload.wikimedia.org/wikipedia/commons/8/8f/CIE_1931_XYZ_Color_Matching_Functions.svg 34 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE XYZ http://upload.wikimedia.org/wikipedia/commons/8/8f/CIE_1931_XYZ_Color_Matching_Functions.svg 35 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE XYZ Tristimulus Developed in 1931 36 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
CIE RGB to XYZ Conversion Positive for visible wavelengths 37 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram Projection of X,Y,Z on the plane z is redundant because 38 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram Given x,y and one tristimulus value (typically Y, hence named CIE xyY) one can recover X,Y and Z like the following 39 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram: D65 D65 – Mid day light Corresponds to 6500K, (actually ~6504K.) (x,y) = 0.3128, 0.3290) D65 40 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram: Complementary Color Color A and B are complementary If Combine(A,B) can produce White Or Gray 41 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram RGB are vertices; can achieve colors inside the triangle by combining them 42 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Chromaticity Diagram RGB are vertices; can achieve colors inside the triangle by combining them 43 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Gamut [gam-uht]: The set of colors representable using a particular display device or color space. 44 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Describing a Display: HDTV Vertices are primaries, possibilities are inside triangle http://upload.wikimedia.org/wikipedia/commons/8/8f/CIExy1931_sRGB.svg 45 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Preception and Color Spaces 46 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Perception of Color 420nm 450nm 590nm 620nm 47 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Perception of Color 420nm 450nm 590nm 620nm 48 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
Perceptual Uniformity • A distance metric in a perceptually uniform color space would corresponds to the visual difference between colors as perceived by human. 49 CS 148: Introduction to Computer Graphics and Imaging (Summer 2016) – Zahid Hossain
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