Chapter 4_ Colour in Images and Video

MULTIMEDIA TECHNOLOGYCOLOUR IN IMAGES AND VIDEO

Dr. Zeeshan Bhatti

BSIT-III

Chapter 4

BY: DR. ZEESHAN BHATTI 1

COLOUR SCIENCE

Light and Spectra

Light is an electromagnetic wave. Its colour is characterized by the wavelength content of the light.

(a) Laser light consists of a single wavelength: e.g., a ruby laser produces a bright, scarlet-red beam.

(b) Most light sources produce contributions over many wavelengths.

(c) However, humans cannot detect all light, just contributions that fall in the \visible wavelengths".

(d) Short wavelengths produce a blue sensation, long wavelengths produce a red one.


SPECTROPHOTOMETER: device used to measure visible light, by reflecting light from a direction grating (a ruled surface) that spreads out the different wavelengths.

Figure shows the phenomenon that white light contains all the colours of a rainbow.

Visible light is an electromagnetic wave in the range 400 nm to 700 nm (where nm stands for nanometer, 10−9 meters).


Why does the prism separate the light into its spectral

components?

prism bends different wavelengths of light by different amounts

refractive index is a function of wavelength

shorter wavelengths are refracted more strongly than longer wavelengths


HUMAN VISION

The eye works like a camera, with the lens focusing an image onto the retina (upside-down and left-right reversed).

The retina consists of an array of rods and three kinds of cones.

The rods come into play when light levels are low and produce a image in shades of gray (\all cats are gray at night!").

For higher light levels, the cones each produce a signal. Because of their diering pigments, the three kinds of cones are most sensitive to red (R), green (G), and blue (B) light.

It seems likely that the brain makes use of differences R-G, G-B, and B-R, as well as combining all of R, G, and B into a high-light-level achromatic channel.


6

COLOUR

Light source, object, observer

Electromagnetic spectrum

BY: DR. ZEESHAN BHATTI

7

THE EYERods and Cones

Rods perceive luminance only

Highly sensitive

Cones perceive colour

Require bright conditions

Red, Green, Blue pigment

3 million behind fovea, 1° - 2 ° of accurate vision

Absorption not even distributed 40:20:1 (RGB)

Better tuned to see red, yellow, green cyan range


COLOR BLINDNESS


Guess The Number in Each Figure ….?

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RGB- ADDITIVE COLOUR

RGB

Full amounts of each light produce white

Like a TV or Monitor


RGB MODEL IS ADDITIVE

Red=Green=Blue=0 is black

(no color)Add Red only

Add some blue How to make pure white?


HSB MODEL

Based on human perception

Hue: color reflected from or transmitted through an object

Saturation: strength of color (% grey)

Brightness: relative lightness from black (0%) to white (100%)


CMYK MODEL

Based on light-absorbing quality of ink printed on paper

As light is absorbed, part of spectrum is absorbed and part reflected back to eyes

So CMYK is a subtractive model (RGB is additive)

4 channels: Cyan (C), magenta (M), yellow (Y), black (K)

In theory, pure colors should produce black, but printing inks contain impurities

So combining 3 pure colors produces muddy brown

Therefore pure K is needed to produce pure black

Hence CMYK is four-color process printing


PRINTING PRESS PROCESS


PRINTING PRESS PROCESS


DIGITAL PRINTING PROCESS


Figure shows colour combinations that result from combining primary colours available in the two situations, additive colour and subtractive colour.

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Fig. Additive and subtractive colour. (a): RGB is used to

specify additive colour. (b): CMY is used to specify subtractive

colorBY: DR. ZEESHAN BHATTI

COLOR GAMUT

Eyes see more than screens or printers can show

Gamut is the range of a color model

RGB and CMYK show different subsets of colors


ALPHA CHANNEL

+ =

Alpha channel stores mask information

A mask lets part of an image be transparent so that other

layers show through

8-bit mask value determines degree of transparency

So Photoshop files have 3 channels for color and 1 alpha

(32 bits per pixel)


CLUT OR PALETTE

8-bit color is low-cost, limited gamut

GIF and web-safe colors are 8-bit

Indexing millions of colors to 256 is arbitrary

Here are some standard and custom palettes

Macintosh CLUT

(Color Look-Up Table) Web-safe palette

(216 colors)


http://www.cse.lehigh.edu/~glennb/mm/pics/palettes.ColorPlate1.jpg

PALETTE ISSUES

What happens when converting from 24- to 8-bit color depth?

Dithering: finding closest possible color in palette

Why might a custom palette be useful?

Matching colors of a photograph

What happens when switching palettes?

Screen flashing

Avoid it by fading images to white or black


HISTORY OF COLOUR


HISTORY OF COLOR

Color came into experience of Human mind because of its frightening nature when it sees huge mammals, earth and other things around it.

Knowing strange about things…to become powerful by get ride of….

Create pictures to controls beast and wild animals…so called black magic through images.


COLOR IN ANCIENT EGYPTMESOPOTAMIA, THE FAR EAST

Based of religion

Light and Shadows

Unaware….Unconcern

Flat Color sculptors

For them sun and Moon is the important things


COLOR IN ANCIENT CRETE

Style was free

Color was always Cheery

Specially in interior of House

flying fish

spiral patterns


COLOR IN ANCIENT GREECE

Strong hand in architecture and sculptor

Renowned Vases with three colors

painting their stone, bronze, and marble statues realistically


COLOR IN ANCIENT ROME

magnificent temples, palaces, and luxurious villas with strong interiors painted with mosaics.

encaustic, pigments mixed with hot wax to create mosaics like a paintings


COLOR IN ANCIENT CHRISTIANITY

Work with glass mosaics rather than stone and marble chips


COLOR IN MUSLIM ERA

Mostly for Religious writings and religious art.

Architectural decoration with shapes and calligraphic

Patterns, geometric shapes and designs.


COLOR IN MUGHAL ERA


PROPERTIES / ATTRIBUTES OF COLOUR


RED (HIGH VOLTAGE, I AM AVAILABLE, ONLY YOU CAN SEE, I WILL

TEASE YOU, DON’T TOUCH ME)

Fire

Blood

Energy

War

Danger

Strength Light red represents joy, sexuality, passion, sensitivity, and

love.

Pink signifies romance, love, and friendship. It denotes

feminine qualities and passiveness.

Dark red is associated with vigor, willpower, rage, anger,

leadership, courage, longing, malice, and wrath.

Brown suggests stability and denotes masculine qualities.

Reddish-brown is associated with harvest and fall.

• Power

• Passion

• Love

• Desire

• Anger


ORANGE (CREATIVITY, ATTRACTION, SUCCESS YOU WILL GET,

YOUNG)

Joy

Sunshine

enthusiasm

Fascination

happiness

Creativity

determination Dark orange can mean deceit and distrust.

Red-orange corresponds to desire, sexual passion,

pleasure, domination, aggression, and thirst for action.

Gold evokes the feeling of prestige. The meaning of gold

is illumination, wisdom, and wealth. Gold often symbolizes

high quality.

• attraction

• success

• encourage

ment

• stimulation


YELLOW (SUNSHINE, NEW DAWN, INTELLECT, HAPPINESS)

warming effect

arouses cheerfulness

generates muscle energy

honor

loyalty

Dull (dingy) yellow represents caution, decay, sickness,

and jealousy.

Light yellow is associated with intellect, freshness, and

joy.

• cowardice


GREEN (NATURE, HEALING POWER, HOPE )

Growth

Harmony

Freshness

Fertility

Emotion Safety

Dark green is associated with ambition, greed, and

jealousy.

Yellow-green can indicate sickness, cowardice, discord,

and jealousy.

Aqua is associated with emotional healing and protection.

Olive green is the traditional color of peace.

• Pure

Money

• hope


BLUE (FUTURE, DREAM, DEPTH STABILITY)

trust

Loyalty

Wisdom

Confidence

intelligence

faith

Light blue is associated with health, healing, tranquility,

understanding, and softness.

Dark blue represents knowledge, power, integrity, and

seriousness.

• Truth

• Heaven

• Sea

• Sky

• Ocean

Depth


PURPLE (POWER, NOBILITY, LUXURY, CAN’T BEAT ME)

Wealth

Extravagance

Wisdom

Dignity

Independence

Creativity

Light purple evokes romantic and nostalgic feelings.

Dark purple evokes gloom and sad feelings. It can cause

frustration.

• Mystery

• Magic

• Royalty

• Artificial


WHITE (GOD, PURE, TRUTH, MOTHER, I WILL BE THERE FOR YOU)

Goodness

Innocence

Purity

Virginity

color of perfection

What ever it takessss , whatever heart breakssss, I will

be right there waiting for you. La..la.lala……lalalala

• Safety

• Cleanliness

• Spirit

• Coolness

• Hospitals

• Doctors

• Sterility


BLACK (DEATH, EVIL)

Power

Elegance

Formality

Death

Evil

Mystery

I will destroy you, break you, give you pain, not leave you

alone

• Fear

• Black holes

• Negative

strength and

authority

• Grief

• Sorrow

• Pain


THANKYOU

Q & A


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Chapter 4_ Colour in Images and Video

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