lecture iii: color in image & video · most sources used for illumination emit white, or...
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LECTURE III
COLOR IN IMAGE amp VIDEO
DR OUIEM BCHIR
1
COLOR SCIENCE
Light and Spectra
Light is a narrow range of electromagnetic energy
Electromagnetic waves have the properties of frequency and
wavelength
The distance from peak to peak of the wave is called the wavelength
Color is characterized by the wavelength content of the light
Laser light consists of a single wavelength eg a ruby laser
produces a bright scarlet-red beam
2
Most light sources produce
contributions over many
wavelengths
1048698 Human cannot detect all light just contributions that fall in the ldquovisible wavelengthsrdquo
Short wavelengths produce a blue sensation long wavelengths produce a red one
The human eye responds to the band of wavelengths between 300nm and 700nm
3
Most sources used for illumination emit white or nearly white
light
Using a prism Newton showed that white light is made up of
contributions from all of the visible wavelengths
4
Spectrophotometer device used to measure visible light by
reflecting light from a diffraction grating (a ruled surface)
that spreads out the different wavelengths
Visible light is electromagnetic wave in [300nm 700nm]
5
White light contains all
the colors of a rainbow
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
COLOR SCIENCE
Light and Spectra
Light is a narrow range of electromagnetic energy
Electromagnetic waves have the properties of frequency and
wavelength
The distance from peak to peak of the wave is called the wavelength
Color is characterized by the wavelength content of the light
Laser light consists of a single wavelength eg a ruby laser
produces a bright scarlet-red beam
2
Most light sources produce
contributions over many
wavelengths
1048698 Human cannot detect all light just contributions that fall in the ldquovisible wavelengthsrdquo
Short wavelengths produce a blue sensation long wavelengths produce a red one
The human eye responds to the band of wavelengths between 300nm and 700nm
3
Most sources used for illumination emit white or nearly white
light
Using a prism Newton showed that white light is made up of
contributions from all of the visible wavelengths
4
Spectrophotometer device used to measure visible light by
reflecting light from a diffraction grating (a ruled surface)
that spreads out the different wavelengths
Visible light is electromagnetic wave in [300nm 700nm]
5
White light contains all
the colors of a rainbow
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Most light sources produce
contributions over many
wavelengths
1048698 Human cannot detect all light just contributions that fall in the ldquovisible wavelengthsrdquo
Short wavelengths produce a blue sensation long wavelengths produce a red one
The human eye responds to the band of wavelengths between 300nm and 700nm
3
Most sources used for illumination emit white or nearly white
light
Using a prism Newton showed that white light is made up of
contributions from all of the visible wavelengths
4
Spectrophotometer device used to measure visible light by
reflecting light from a diffraction grating (a ruled surface)
that spreads out the different wavelengths
Visible light is electromagnetic wave in [300nm 700nm]
5
White light contains all
the colors of a rainbow
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Most sources used for illumination emit white or nearly white
light
Using a prism Newton showed that white light is made up of
contributions from all of the visible wavelengths
4
Spectrophotometer device used to measure visible light by
reflecting light from a diffraction grating (a ruled surface)
that spreads out the different wavelengths
Visible light is electromagnetic wave in [300nm 700nm]
5
White light contains all
the colors of a rainbow
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Spectrophotometer device used to measure visible light by
reflecting light from a diffraction grating (a ruled surface)
that spreads out the different wavelengths
Visible light is electromagnetic wave in [300nm 700nm]
5
White light contains all
the colors of a rainbow
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
HOW MATERIALS MODIFY
LIGHT
Vision occurs when light from surrounding objects reaches the eye
Materials modify the light incident upon them in several ways
Light can be reflected from a surface
Light can be absorbed by or transmitted through a surface
In many cases light is both absorbed by and reflected from a surfaces
The amount of absorption and reflection depends on the wavelength resulting in some wavelengths being absorbed and others reflected to varying degrees
The wavelengths that are reflected from an object and perceived by the human eye is what gives an object its color
6
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
In this example
red light is reflected
Blue and green are absorbed
Object appears red
7
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Light can be transmitted or passed through an object in varying
degrees The amount of transmission can also be dependent on
the wavelength
8
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Light is passed through from a
colorless transparent object
unchanged
Object will appear clear
(eg window)
9
Light is partially transmitted
Certain wavelengths are
transmitted others are absorbed
This type of objects appear
translucent and colored (eg
colored glass)
This is the principle behind absorptive filters which are used to
remove or pass certain wavelengths of light
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
A surface can create the perception of color by absorbing
certain wavelengths and reflecting others
10
Inks are formulated to absorb certain
wavelengths while reflecting others
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Only wavelengths that are present can be reflected
An object will appear its ldquousualrdquo color under white light because
all wavelengths are present to be reflected
11
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
A ldquoredrdquo apple appears red
under white light because red
is reflected and other
wavelengths are absorbed
12
Apple is illuminated with
light of a single color
(green)
bull No wavelength in the red region
to be reflected
bull All light is absorbed
bull Apple appears dark
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
The apparent color of an object is the
product of
1 Object characteristics
2 Light source used for illumination of that object
+
Human vision
13
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
HUMAN VISION
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
14
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
SPECTRAL SENSITIVITY
OF THE EYE
The eye is most sensitive to light in the middle of the visible
spectrum
The sensitivity of our receptors is also a function of
wavelength
The Blue receptor sensitivity is much smaller than the Red and
Green
15
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Luminous-efficiency function= Overall sensitivity
1048698 Denoted V(λ)
1048698 Formed as the sum of the response curves for Red Green and Blue
16
R G and B cones and
Luminance Efficiency
curve
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
IMAGE FORMATION
MODEL
17
C(λ) Color signal
C(λ ) = E(λ )S(λ )
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
CAMERA SYSTEMS
1048698 Camera systems are made in a similar fashion a studio-quality
camera has three signals produced at each pixel location
(corresponding to a retinal position)
1048698 Analog signals are converted to digital truncated to integers
and stored
1048698 If the precision used is 8-bit then the maximum value for any of
R G B is 255 and the minimum is 0
1048698 However the light entering the eye of the computer user is that
which is emitted by the screen Therefore we need to know the
light E(λ) entering the eye
18
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
GAMMA CORRECTION
1048698 The light emitted is in fact roughly proportional to the voltage
raised to a power this power is called gamma (γ)
1048698 If the value in the red channel is R
1048698 The screen emits light proportional to R^γ
1048698 The value of gamma is around 22
19
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
EFFECT OF CRT ON LIGHT EMITTED
FROM SCREEN
Light output with no gamma-correction applied
darker values are displayed too dark
20
Effect of pre-correcting signals by applying the power law R1γ
21
Effect of pre-correcting signals by applying the power law R1γ
21
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