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Multimedia Systems Part 6 Mahdi Vasighi www.iasbs.ac.ir/~vasighi Department of Computer Science and Information Technology, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran

Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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Page 1: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

Page 2: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

To discuss …

o Color Scienceo Color Models in image

Page 3: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

Light & SpectraLight is an electromagnetic wave

• It’s color is characterized by its wavelength

Page 4: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

Light & SpectraLight is an electromagnetic wave

• It’s color is characterized by its wavelength

Page 5: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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)

Page 6: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

o λ vs. Spectral power curve is called spectral powerdistribution E(λ)

Page 7: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

Human Visiono Eye resembles a camera focusing image into the retinao Retina consists of an array of rods and cones

Page 8: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

Human Visiono The rods when light levels are low gray imageso The cones higher light level color images

Page 9: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Human Visiono The 3 kinds of cones are more sensitive to R, G & B

present in the ratios 40:20:1

Color Science

Page 10: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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/

Page 11: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Color Science

Human Visiono Eye is most sensitive to the middle of the visible

spectrum

Page 12: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

Page 13: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

Page 14: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Gamma Correction

o The RGB in the image files are converted to analog & drivethe electron guns of CRT

o Perfect case:

Page 15: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

Page 16: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

� ∝ ���

�� ∝ �

��

Page 17: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

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

Page 18: Multimedia Systemsvasighi/courses/multimed1.96/multi... · 2018. 10. 21. · Multimedia Systems Part 6 Mahdi Vasighi vasighi Department of Computer Science and Information Technology,

Gamma Correction