multimedia systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · multimedia systems...
TRANSCRIPT
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Multimedia SystemsPart 6
Mahdi Vasighiwww.iasbs.ac.ir/~vasighi
Department of Computer Science and Information Technology,Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
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To discuss …
o Color Scienceo Color Models in image
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Color Science
Light & SpectraLight is an electromagnetic wave
• It’s color is characterized by its wavelength
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Color Science
Light & SpectraLight is an electromagnetic wave
• It’s color is characterized by its wavelength
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Color Science
o Most light sources produce contributions over many wavelengths.
o contributions that fall only in the visible wavelength can be seen.
o Light from 400 to 700 nanometer (10-9 meter)
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Color Science
o λ vs. Spectral power curve is called spectral powerdistribution E(λ)
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Color Science
Human Visiono Eye resembles a camera focusing image into the retinao Retina consists of an array of rods and cones
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Color Science
Human Visiono The rods when light levels are low gray imageso The cones higher light level color images
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Human Visiono The 3 kinds of cones are more sensitive to R, G & B
present in the ratios 40:20:1
Color Science
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Color Science
Human Visiono brain combines or subtract the excitement between
different cones.
o Yellow is also colorblind-safe!
https://visual.ly/blog/the-use-of-yellow-in-data-design/
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Color Science
Human Visiono Eye is most sensitive to the middle of the visible
spectrum
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Color Science
Let us denote the spectral sensitivity of R, G, B cones asa vector q(λ)
The response in each color channel in the eye isproportional to the number of neurons firing.
These equations quantify the signals transmitted to thebrain
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Color Science
o we actually receive the light that is reflected from a surface. o Surfaces reflect different amounts of light at different s
color signal
Spectral Power Distribution
eye’s cone functions
reflectancefunction
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Gamma Correction
o The RGB in the image files are converted to analog & drivethe electron guns of CRT
o Perfect case:
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Gamma Correction
o The RGB in the image files are converted to analog & drivethe electron guns of CRT
o The CRT light is not linear to the voltage applied, it isproportional to voltage raised to the power, called gamma
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Gamma Correction
o The RGB in the image files are converted to analog & drivethe electron guns of CRT
o This effect can be pre-corrected by applying inversetransformation
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Gamma Correction
o The RGB in the image files are converted to analog & drivethe electron guns of CRT
o The CRT light is not linear to the voltage applied, it isproportional to voltage raised to the power, called gamma
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Gamma Correction