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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
To discuss …
o Color Scienceo Color Models in image
Color Science
Light & SpectraLight is an electromagnetic wave
• It’s color is characterized by its wavelength
Color Science
Light & SpectraLight is an electromagnetic wave
• It’s color is characterized by its wavelength
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)
Color Science
o λ vs. Spectral power curve is called spectral powerdistribution E(λ)
Color Science
Human Visiono Eye resembles a camera focusing image into the retinao Retina consists of an array of rods and cones
Color Science
Human Visiono The rods when light levels are low gray imageso The cones higher light level color images
Human Visiono The 3 kinds of cones are more sensitive to R, G & B
present in the ratios 40:20:1
Color Science
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/
Color Science
Human Visiono Eye is most sensitive to the middle of the visible
spectrum
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
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
Gamma Correction
o The RGB in the image files are converted to analog & drivethe electron guns of CRT
o Perfect case:
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
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
Gamma Correction
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