Free Essay

Video Processing

In: Science

Submitted By amrishsoni
Words 4501
Pages 19
Basics of Video

Yao Wang
Polytechnic University, Brooklyn, NY11201 yao@vision.poly.edu Outline






Color perception and specification
Video capture and display
Analog raster video
Analog TV systems
Digital video

© Yao Wang, 2004

Video Basics

Color Perception and Specification






Light -> color perception
Human perception of color
Type of light sources
Trichromatic color mixing theory
Specification of color
– Tristimulus representation
– Luminance/Chrominance representation

• Color coordinate conversion

© Yao Wang, 2004

Video Basics

3

Light is part of the EM wave

from [Gonzalez02]

© Yao Wang, 2004

Video Basics

4

Illuminating and Reflecting Light
• Illuminating sources:
– emit light (e.g. the sun, light bulb, TV monitors)
– perceived color depends on the emitted freq.
– follows additive rule
• R+G+B=White

• Reflecting sources:
– reflect an incoming light (e.g. the color dye, matte surface, cloth) – perceived color depends on reflected freq (=emitted freqabsorbed freq.)
– follows subtractive rule
• R+G+B=Black
© Yao Wang, 2004

Video Basics

5

Eye Anatomy

From http://www.stlukeseye.com/Anatomy.asp
© Yao Wang, 2004

Video Basics

6

Eye vs. Camera

Camera components

Eye components

Lens

Lens, cornea

Shutter

Iris, pupil

Film

Retina

Cable to transfer images

Optic nerve send the info to the brain

© Yao Wang, 2004

Video Basics

7

Human Perception of Color


Retina contains photo receptors
– Cones: day vision, can perceive color tone • Red, green, and blue cones
• Different cones have different frequency responses • Tri-receptor theory of color vision
[Young1802]

– Rods: night vision, perceive brightness only •

Color sensation is characterized by

From http://www.macula.org/anatomy /retinaframe.html

– Luminance (brightness)
– Chrominance
• Hue (color tone)
• Saturation (color purity)
© Yao Wang, 2004

Video Basics

8

Frequency Responses of Cones

from [Gonzalez02]

Ci = ∫ C (λ )ai (λ )dλ , i = r , g , b, y
© Yao Wang, 2004

Video Basics

9

Frequency Responses of Cones and the Luminous Efficiency Function
100

Relative sensitivity

80

Blue 20
Luminosity
function
Red
Green

60

40

20

0
400

500

600

700

Wavelength

Ci = ∫ C (λ )ai (λ )dλ , i = r , g , b, y
© Yao Wang, 2004

Video Basics

10

Color Hue Specification

© Yao Wang, 2004

Video Basics

11

Trichromatic Color Mixing


Trichromatic color mixing theory
– Any color can be obtained by mixing three primary colors with a right proportion
C = ∑ Tk Ck , Tk : Tristimulus values k =1, 2,3



Primary colors for illuminating sources:
– Red, Green, Blue (RGB)
– Color monitor works by exciting red, green, blue phosphors using separate electronic guns



Primary colors for reflecting sources (also known as secondary colors): – Cyan, Magenta, Yellow (CMY)
– Color printer works by using cyan, magenta, yellow and black
(CMYK) dyes

© Yao Wang, 2004

Video Basics

12

RGB vs CMY

© Yao Wang, 2004

Video Basics

13

red

Blue

Green
© Yao Wang, 2004

Video Basics

14

Color Representation Models


Specify the tristimulus values associated with the three primary colors – RGB
– CMY



Specify the luminance and chrominance
– HSI (Hue, saturation, intensity)
– YIQ (used in NTSC color TV)
– YCbCr (used in digital color TV)



Amplitude specification:
– 8 bits for each color component, or 24 bits total for each pixel
– Total of 16 million colors
– A true RGB color display of size 1Kx1K requires a display buffer memory size of 3 MB

© Yao Wang, 2004

Video Basics

15

Color Coordinate Conversion
• Conversion between different primary sets are linear
(3x3 matrix)
• Conversion between primary and XYZ/YIQ/YUV are also linear
• Conversion to LSI/Lab are nonlinear
– LSI and Lab coordinates
• coordinate Euclidean distance proportional to actual color difference • Conversion formulae between many color coordinates can be found in [Gonzalez92]

© Yao Wang, 2004

Video Basics

16

Video Capture and Display






Light reflection physics
Imaging operator
Color capture
Color display
Component vs. composite video

© Yao Wang, 2004

Video Basics

17

Video Capture
• For natural images we need a light source (λ: wavelength of the source) ?
.
– E (x, y, z, λ): incident light on a point (x, y, z world coordinates of the point)
• Each point in the scene has a reflectivity function.
– r(x, y, z, λ): reflectivity function
• Light reflects from a point and the reflected light is captured by an imaging device.
– c(x, y, z, λ) = E (x, y, z, λ) × r(x, y, z, λ): reflected light.

Courtesy of Onur Guleryuz
© Yao Wang, 2004

Video Basics

18

More on Video Capture
• Reflected light to camera
– Camera absorption function ψ ( X, t ) = ∫ C ( X, t , λ )ac (λ )dλ

– Projection from 3-D to 2-D

X→x
P

ψ ( P( X), t ) = ψ ( X, t ) or ψ (x, t ) = ψ ( P −1 (x), t )
• The projection operator is non-linear
– Perspective projection
– Othographic projection
© Yao Wang, 2004

Video Basics

19

Perspective Projection Model
Y
X
Y

3-D point Z

X
X
Z

C y F

x

Camera center x=F x Y
X
,y=F
Z
Z

y x Image plane © Yao Wang, 2004

The image of an object is reversed from its
3-D position. The object appears smaller when it is farther away.

2-D image Video Basics

20

How to Capture Color
• Need three types of sensors
• Complicated digital processing is incorporated in advanced cameras
2 fs,1/ fs,2
Rate
conv.

Matrix & encoder

2fs,1

Nonlinear processing Color corrector

B

Image enhancer Interpolation

G

fs,1

Pre-process

R

Analog process

Lens

A/D

fs,1

( fs,1)
CCDs

Digital CN output 2fs,1
13.5 MHz

D/A

Analog CN &
CS output

D/A

Viewfinder output Figure 1.2 Schematic block diagram of a professional color video camera. Reprinted from
Y. Hashimoto, M. Yamamoto, and T. Asaida, Cameras and display systems, IEEE (July 1995),
83(7):1032–43. Copyright 1995 IEEE.
© Yao Wang, 2004

Video Basics

21

Video Display
• CRT vs LCD
• Need three light sources projecting red, green, blue components respectively

© Yao Wang, 2004

Video Basics

22

Analog Video
• Video raster
• Progressive vs. interlaced raster
• Analog TV systems

© Yao Wang, 2004

Video Basics

23

Raster Scan
• Real-world scene is a continuous 3-D signal
(temporal, horizontal, vertical)
• Analog video is stored in the raster format
– Sampling in time: consecutive sets of frames
• To render motion properly, >=30 frame/s is needed

– Sampling in vertical direction: a frame is represented by a set of scan lines
• Number of lines depends on maximum vertical frequency and viewing distance, 525 lines in the NTSC system

– Video-raster = 1-D signal consisting of scan lines from successive frames

© Yao Wang, 2004

Video Basics

24

Progressive and Interlaced Scans
Interlaced Frame

Progressive Frame
Horizontal retrace

Field 1

Field 2

Vertical retrace

Interlaced scan is developed to provide a trade-off between temporal and vertical resolution, for a given, fixed data rate (number of line/sec).
© Yao Wang, 2004

Video Basics

25

Waveform and Spectrum of an
Interlaced Raster
Horizontal retrace for first field

Vertical retrace from first to second field

Vertical retrace from second to third field

Blanking level
Black level
Th

White level

Tl

T

T

t
2
t

(a)
(f)

0

fl

2 fl

3 fl

fmax

f

(b)

© Yao Wang, 2004

Video Basics

26

Color TV Broadcasting and Receiving

RGB
--->
YC1C2

Luminance,
Chrominance,
Audio
Multiplexing

Modulation

YC1C2
--->
RGB

DeMultiplexing

DeModulation

© Yao Wang, 2004

Video Basics

27

Why not using RGB directly?


R,G,B components are correlated
– Transmitting R,G,B components separately is redundant
– More efficient use of bandwidth is desired



RGB->YC1C2 transformation
– Decorrelating: Y,C1,C2 are uncorrelated
– C1 and C2 require lower bandwidth
– Y (luminance) component can be received by B/W TV sets



YIQ in NTSC
– I: orange-to-cyan
– Q: green-to-purple (human eye is less sensitive)
• Q can be further bandlimited than I

– Phase=Arctan(Q/I) = hue, Magnitude=sqrt (I^2+Q^2) = saturation
– Hue is better retained than saturation
© Yao Wang, 2004

Video Basics

28

Color Image

I image (orange-cyan)

Y image

Q image (green-purple)

I and Q on the color circle
Q: green-purple

I: orange-cyan

© Yao Wang, 2004

Video Basics

30

Conversion between RGB and YIQ
• RGB -> YIQ
Y = 0.299 R + 0.587 G + 0.114 B
I = 0.596 R -0.275 G -0.321 B
Q = 0.212 R -0.523 G + 0.311 B
• YIQ -> RGB
R =1.0 Y + 0.956 I + 0.620 Q,
G = 1.0 Y - 0.272 I -0.647 Q,
B =1.0 Y -1.108 I + 1.700 Q.
© Yao Wang, 2004

Video Basics

31

TV signal bandwidth


Luminance
– Maximum vertical frequency (cycles/picture-height)= black and white lines interlacing f v,max = Kf 's , y / 2
– Maximum horizontal frequency (cycles/picture-width) f h,max = f v,max ⋅ IAR
– Corresponding temporal frequency (cycles/second or Hz) f max = f h,max / T 'l = IAR ⋅ Kf 's , y /2T 'l
– For NTSC,



f max = 4.2 MHz

Chrominance
– Can be bandlimited significantly
• I: 1.5 MHz, Q: 0.5 MHz.

© Yao Wang, 2004

Video Basics

32

Bandwidth of Chrominance Signals






Theoretically, for the same line rate, the chromiance signal can have as high frequency as the luminance signal
However, with real video signals, the chrominance component typically changes much slower than luminance
Furthermore, the human eye is less sensitive to changes in chrominance than to changes in luminance
The eye is more sensitive to the orange-cyan range (I) (the color of face!) than to green-purple range (Q)
The above factors lead to
– I: bandlimitted to 1.5 MHz
– Q: bandlimitted to 0.5 MHz

© Yao Wang, 2004

Video Basics

33

Multiplexing of Luminance and
Chrominance


Chrominance signal can be bandlimited
– it usually has a narrower frequency span than the luminance and the human eye is less sensitive to high frequencies in chrominance



The two chrominance components (I and Q) are multiplexed onto the same sub-carrier using QAM
– The upper band of I is limited to 0.5 MHz to avoid interference with audio •



Position the bandlimited chrominance at the high end spectrum of the luminance, where the luminance is weak, but still sufficiently lower than the audio (at 4.5 MHz=286 fl)
The actual position should be such that the peaks of chrominance spectrum interlace with those of the luminance f c = 455 fl / 2 ( = 3.58 Hz for NTSC)

© Yao Wang, 2004

Video Basics

34

Spectrum Illustration

(f )

0

Luminance

fl

2 fl

3 fl

Chrominance

225 fl 226 fl 227 fl 228 fl

229 fl 230 fl

f

fc
(Color subcarrier)

© Yao Wang, 2004

Video Basics

35

Multiplexing of luminance, chrominance and audio
(Composite Video Spectrum)
6.0 MHz

Luminance
I
I and Q
Audio

4.5 MHz
1.25
MHz

4.2 MHz
3.58 MHz

fc

fp

fa

f

Color
Audio
subcarrier subcarrier

Picture carrier (b)
© Yao Wang, 2004

Video Basics

36

Quadrature Amplitude Modulation
(QAM)
• A method to modulate two signals onto the same carrier frequency, but with 90o phase shift cos( 2π f1t )

cos( 2π f1t )

s1 ( t ) m (t )

LPF

m (t )

LPF

s 2 (t )

s 2 (t )

sin( 2π f1t )

sin( 2π f1t )

QAM modulator

© Yao Wang, 2004

s1 ( t )

QAM demodulator

Video Basics

37

Adding Color Bursts for
Synchronization

For accurate regeneration of the color sub-carrier signal at the receiver, a color burst signal is added during the horizontal retrace period
Figure from From Grob, Basic Color Television Principles and Servicing, McGraw Hill, 1975 http://www.ee.washington.edu/conselec/CE/kuhn/ntsc/95x417.gif © Yao Wang, 2004

Video Basics

38

Multiplexing of Luminance and
Chrominance
Y(t)

I(t)

LPF
0-4.2MHz

LPF
0-1.5MHz

-π/2
Q(t)

Σ

BPF
2-4.2MHz

LPF
0-0.5MHz
Gate


Acos(2πfct)
© Yao Wang, 2004

Video Basics

Σ
Composite
video

Color burst signal 39

DeMultiplexing of Luminance and
Chrominance
Composite video Y(t)

Comb Filter
0-4.2MHz

+

LPF
0-1.5MHz



I(t)

Horizontal sync signal

Gate

2Acos(2πfct)

Phase comparator © Yao Wang, 2004



-π/2
LPF
0-0.5MHz

Q(t)

Voltage controlled oscillator
Video Basics

40

Luminance/Chrominance Separation


In low-end TV receivers, a low pass filter with cut-off frequency at 3MHz is typically used to separate the luminance and chrominance signal.
– The high frequency part of the I component (2 to 3 Mhz) is still retained in the luminance signal.
– The extracted chrominance components can contain significant luminance signal in a scene with very high frequency (luminance energy is not negligible near fc)
– These can lead to color bleeding artifacts




For better quality, a comb filter can be used, which will filter out harmonic peaks correspond to chrominance signals.
Show example of comb filter on board

© Yao Wang, 2004

Video Basics

41

What will a Monochrome TV see?
• The monochrome TV receiver uses a LPT with cut-off at 4.2 MHz, and thus will get the composite video
(baseband luminance plus the I and Q signal modulated to fc =3.58 MHz)
– Because the modulated chrominance signal is at very high frequency (227.5 cycles per line), the eye smoothes it out mostly, but there can be artifacts
– The LPF in Practical TV receivers have wide transition bands, and the response is already quite low at fc.

© Yao Wang, 2004

Video Basics

42

Color TV Broadcasting and Receiving

RGB
--->
YC1C2

Luminance,
Chrominance,
Audio
Multiplexing

Modulation

YC1C2
--->
RGB

DeMultiplexing

DeModulation

© Yao Wang, 2004

Video Basics

43

Transmitter in More Details
Audio

FM modulator
4.5MHz

R(t)

B(t)

RGB to YIQ conversion

G(t)

Y(t)

LPF
0-4.2MHz

I(t)

LPF
0-1.5MHz

-π/2
Q(t)

Σ

BPF
2-4.2MHz



Acos(2πfct)
© Yao Wang, 2004

Video Basics

VSB
To
transmit antenna LPF
0-0.5MHz
Gate

Σ

Color burst signal
44

Receiver in More Details
Audio



Gate
VSB
Demodulator
From antenna

Y(t)

Comb Filter
0-4.2MHz

2Acos(2πfct)

+

LPF
0-1.5MHz

I(t)

-π/2



LPF
0-0.5MHz

R(t)
YIQ to RGB conversion

BPF, 0-4.2 MHz

BPF, 4.4-4.6MHz

Composite video To speaker G(t)

To CRT

FM demodulator

B(t)

Q(t)

Voltage
Phase
controlled comparator oscillator
Horizontal
sync signal

© Yao Wang, 2004

Video Basics

45

Matlab Simulation of Mux/Demux
• We will show the multiplexing/demultiplexing of YIQ process for a real sequence (‘mobile calendar’)
– Original Y,I, Q frames
– Converted Y,I, Q raster signals and their respective spectrums – QAM of I and Q: choice of fc, waveform and spectrum
– Multiplexing of Y and QAM(I+Q): waveform and spectrum
– What wil a B/W TV receiver see:
• W/o filtering vs. with filtering

– What will a color TV receiver see:
• Original and recovered Y,I, Q
• Original and recovered color image
• Spectrum and waveforms

© Yao Wang, 2004

Video Basics

46

Spectrum of Y, I, Q
10

10

10

10

10

10

10

10

Y S pectrum

6

10

5

10

4

10

3

10

2

10

1

10

0

10

-1

0

5

10

10 x 10

I S pectrum

6

10

5

10

4

10

3

10

2

10

1

10

0

10

-1

0

5

5

10

10 x 10

Q S pectrum

6

5

4

3

2

1

0

-1

0

5

10

5

x 10

Spectrum of Y, I, and Q components, computed from first two progressive frames of “mobilcal”, 352x240/frame
Maximum possible frequency is 352x240x30/2=1.26 MHz.
Notice bandwidths of Y, I, Q components are 0.8,0.2,0.15 MHz, respectively, if we consider 10^3 as the cut-off magnitude.
© Yao Wang, 2004

Video Basics

47

5

QAM of I and Q: Waveform
I Waveform

Q Waveform

QAM multiplexed I & Q

60

60

40

40

40

20

20

20

0

Gra y Level

80

Gra y Level

80

60

Gra y Level

80

0

0

-20

-20

-20

-40

-40

-40

-60

-60

-60

-80

0

0.5

1
Time

1.5 x 10

-4

-80

0

0.5

1
Time

1.5 x 10

-4

-80

0

0.5

1
Time

1.5 x 10

Line rate fl =30*240; Luminance fmax=30*240*352/2*0.7=.89 MHz, The color subcarrier fc=225*fl /2=0.81MHz.
M(t)=I(t)*cos(2πfct)+Q(t)*sin (2πfct)
© Yao Wang, 2004

Video Basics

48

-4

QAM of I and Q: Spectrum
10

10

10

10

10

10

10

10

I S pectrum

6

10

5

10

4

10

3

10

2

10

1

10

0

10

-1

0

5

10

10 x 10

Q S pectrum

6

10

5

10

4

10

3

10

2

10

1

10

0

10

-1

0

5

5

10

10 x 10

QAM I+Q S pectrum

6

5

4

3

2

1

0

-1

0

5

10

5

x 10

Spectrum of I, Q, and QAM multiplexed I+Q, fc=225*fl/2=0.81 MHz
© Yao Wang, 2004

Video Basics

49

5

Composite Video: Waveform
Y Waveform

Compos ite Waveform

200

150

150
Gray Level

250

200

Gray Level

250

100

100

50

0

50

0

0.5

1
Time

1.5 x 10

-4

0

0

0.5

1
Time

1.5 x 10

-4

Waveform of the Y signal Y(t) and the composite signal V(t)=Y(t)+M(t). 1 line
© Yao Wang, 2004

Video Basics

50

Composite Video: Spectrum
10

10

10

10

10

Y S pectrum

6

10

5

10

4

10

3

10

2

0

2

4

6

8

10

12 x 10

© Yao Wang, 2004

10
5

Compos ite Video S pectrum

6

5

4

3

2

0

2

4

6

8

10

12 x 10

Video Basics

5

51

Blown-up View of Spectrum
10

Compos ite S pectrum (beginning)

6

10

6

Compos ite S pectrum (near fc )

Chrominance peaks Luminance peaks
10

10

10

5

10

4

10

3

10

5

4

3

Luminance peaks
10

2

0

5

10

10

15 x 10

2

7.5

8

4

8.5

9 x 10

5

Notice the harmonic peaks of Y and M interleaves near fc
© Yao Wang, 2004

Video Basics

52

Composite Video Viewed as a
Monochrome Image w/o filtering
Original Y

Composite Signal as Y

On the right is what a B/W receiver will see if no filtering is applied to the baseband video signal

© Yao Wang, 2004

Video Basics

53

Low-Pass Filter for Recovering Y

Frequency response

Impulse response (filter coefficients)

Ma gnitude (dB)

50

0.6

0

0.5
-50

0.4

-100
-150

0

2

4

6
8
Fre que ncy (Hz)

10

0.3

12 x 10

5

P has e (degrees )

0

0.2

-500

0.1

-1000

-1500

0

0

2

4

6
8
Fre que ncy (Hz)

10

12

-0.1

x 10

5

0

5

10

15

20

25

f_LPF=30*240/2*150=0.54MHz; fir_length=20;
LPF=fir1(fir_length,f_LPF/(Fs/2));
© Yao Wang, 2004

Video Basics

54

Recovered Y with Filtering

Original Y

Recovered Y

On the right is what a B/W receiver will see if a lowpass filter with cutoff frequency at about 0.75 MHz is applied to the baseband video signal. This is also the recovered Y component by a color receiver if the same filter is used to separate Y and QAM signal.
Y’(t)=conv(V(t),LPF(t))
© Yao Wang, 2004

Video Basics

55

Y Waveform Comparison
Y Waveform

Compos ite Waveform

Y from Compos ite us ing LP F

200

200

150

150

150

Gray Level

250

Gray Level

250

200

Gray Level

250

100

100

100

50

50

50

0

0

0.5

1
Time

© Yao Wang, 2004

1.5 x 10

-4

0

0

0.5

1
Time

Video Basics

1.5 x 10

-4

0

0

0.5

1

1.5

Time

x 10

56

-4

Demux Y and QAM(I,Q)
QAM Waveform

Demultiplexed QAM

60

40

40

20

20
Gray Level

80

60

Gray Level

80

0

0

-20

-20

-40

-40

-60

-60

-80

0

0.5

1
Time

1.5 x 10

-4

-80

0

0.5

1
Time

1.5 x 10

-4

M’(t)=V(t)-Y’(t)
© Yao Wang, 2004

Video Basics

57

QMA Modulation and Demodulation


Modulated signal:
– M(t)=I(t)*cos(2πfct)+Q(t)*sin (2πfct)



Demodulated signal:
– I’(t)=2*M(t)*cos(2πfct), Q’(t)=2*M(t)*sin(2πfct)
– I’(t) contains I(t) at baseband, as well as I(t) at 2fc and Q(t) at 4fc
– A LPF is required to extract I(t)

cos( 2π f1t )

cos( 2π f1t )

s1 ( t ) m (t )

LPF

m (t )

LPF

s 2 (t )

s 2 (t )

sin( 2π f1t )

sin( 2π f1t )

QAM modulator
© Yao Wang, 2004

s1 ( t )

QAM demodulator
Video Basics

58

Lowpass filter for Extracting QAM(I+Q)
Frequency response

Impulse response

Magnitude (dB)

50

0.16
0.14

0

0.12

-50

0.1

-100

0

2

4

6
8
Frequency (Hz)

10

12 x 10

5

0.08

P has e (degrees )

0

0.06

-200

0.04

-400

0.02

-600

0

-800

0

2

4

6
8
Frequency (Hz)

10

-0.02

12 x 10

5

0

5

10

15

20

25

f_LPF=0.2MHz; fir_length=20;
LPF=fir1(fir_length,f_LPF/(Fs/2));
© Yao Wang, 2004

Video Basics

59

QAM Demodulation: Waveform
Original I

Demodulated I

Demodulation+LP F I

60

60

40

40

40

20

20

20

0

Gray Level

80

Gray Level

80

60

Gray Level

80

0

0

-20

-20

-20

-40

-40

-40

-60

-60

-60

-80

0

0.5

1
Time

1.5 x 10

-4

-80

0

0.5

1
Time

1.5 x 10

I’(t)=2*M(t)*cos(2πfct)
© Yao Wang, 2004

Video Basics

-4

-80

0

0.5

1
Time

1.5 x 10

I’’(t)=conv(I’(t),LPF(t))
60

-4

QAM Demodultion: Spectrum
10

10

10

10

10

I S pectrum

6

10

5

10

4

10

3

10

2

0

5

10

10 x 10

© Yao Wang, 2004

Extracted I S pectrum w/o LP F

6

10

5

10

4

10

3

10

2

0

5

5

10

10 x 10

Video Basics

5

Extracted I S pectrum after LP F

6

5

4

3

2

0

5

10 x 10

61

5

original I

original Q

50

50

100

100

150

150

200

200
100

200

300

100

Recovered I

200

300

Recovered Q

50

50

100

100

150

150

200

200
100

© Yao Wang, 2004

200

300

100
Video Basics

200

300
62

Original color frame

Recovered color frame
© Yao Wang, 2004

Video Basics

63

Different Color TV Systems

Parameters

NTSC

PAL

SECAM

Field Rate (Hz)

59.95 (60)

50

50

Line Number/Frame

525

625

625

Line Rate (Line/s)

15,750

15,625

15,625

Color Coordinate

YIQ

YUV

YDbDr

Luminance Bandwidth (MHz)

4.2

5.0/5.5

6.0

Chrominance Bandwidth (MHz)

1.5(I)/0.5(Q)

1.3(U,V)

1.0 (U,V)

Color Subcarrier (MHz)

3.58

4.43

4.25(Db),4.41(Dr)

Color Modulation

QAM

QAM

FM

Audio Subcarrier

4.5

5.5/6.0

6.5

Total Bandwidth (MHz)

6.0

7.0/8.0

8.0

© Yao Wang, 2004

Video Basics

64

Who uses what?

From http://www.stjarnhimlen.se/tv/tv.html#worldwide_0
© Yao Wang, 2004

Video Basics

65

Digital Video
• Digital video by sampling/quantizing analog video raster BT.601 video
• Other digital video formats and their applications

© Yao Wang, 2004

Video Basics

66

Digitizing A Raster Video



Sample the raster waveform = Sample along the horizontal direction Sampling rate must be chosen properly
– For the samples to be aligned vertically, the sampling rate should be multiples of the line rate
– Horizontal sampling interval = vertical sampling interval
– Total sampling rate equal among different systems f s = 858 fl (NTSC) = 864 fl (PAL/SECAM) = 13.5 MHz

© Yao Wang, 2004

Video Basics

67

BT.601* Video Format

858 pels

864 pels

Active
Area

122 pel 16 pel 576 lines

720 pels
625 lines

480 lines

525 lines

720 pels

Active
Area

132 pel 525/60: 60 field/s

12 pel 625/50: 50 field/s

* BT.601 is formerly known as CCIR601
© Yao Wang, 2004

Video Basics

68

RGB YCbCr

Y_d = 0.257 R_d + 0.504 G_d + 0.098 B_d + 16,
C_b = -0.148 R_d - 0.291 G_d + 0.439 B_d + 128,
C_r = 0.439 R_d -0.368 G_d - 0.071 B_d + 128,
R_d = 1.164 Y_d’ + 0.0 C_b’+ 1.596 C_r’,
G_d = 1.164 Y_d’ - 0.392 C_b’ -0.813 C_r’,
B_d = 1.164 Y_d’ + 2.017 C_b’ + 0.0 C_r’,
Y_d’=Y_d -16, C_b’=C_b-128, C_r’=C_r-128

© Yao Wang, 2004

Video Basics

69

Chrominance Subsampling Formats

4:4:4
For every 2x2 Y Pixels
4 Cb & 4 Cr Pixel
(No subsampling)

4:2:2
For every 2x2 Y Pixels
2 Cb & 2 Cr Pixel
(Subsampling by 2:1 horizontally only)

4:1:1
For every 4x1 Y Pixels
1 Cb & 1 Cr Pixel
(Subsampling by 4:1 horizontally only)
Cb and Cr Pixel

Y Pixel

© Yao Wang, 2004

4:2:0
For every 2x2 Y Pixels
1 Cb & 1 Cr Pixel
(Subsampling by 2:1 both horizontally and vertically)

Video Basics

70

Digital Video Formats
Video Format

Frame Rate
(Hz)

Raw Data Rate
(Mbps)

H DTV Over air. cable, satellite, MPEG2 video, 20-45 Mbps
S MPTE296M
1280x720
4:2:0
SMPTE295M
1920x1080
4:2:0

24P/30P/60P
24P/30P/60I

265/332/664
597/746/746

Video production, MPEG2, 15-50 Mbps
BT.601
720x480/576
BT.601
720x480/576

60I/50I
60I/50I

249
166

High quality video distribution (DVD, SDTV), MPEG2, 4-10 Mbps
BT.601
720x480/576
4:2:0
60I/50I

124

Intermediate quality video distribution (VCD, WWW), MPEG1, 1.5 Mbps
SIF
352x240/288
4:2:0
30P/25P

30

Video conferencing over ISDN/Internet, H.261/H.263, 128-384 Kbps
CIF
352x288
4:2:0
30P

37

Video telephony over wired/wireless modem, H.263, 20-64 Kbps
QCIF
176x144
4:2:0
30P

9.1

© Yao Wang, 2004

Y Size

Color
Sampling

4:4:4
4:2:2

Video Basics

71

Video Terminology


Component video







Three color components stored/transmitted separately
Use either RGB or YIQ (YUV) coordinate
New digital video format (YCrCb)
Betacam (professional tape recorder) use this format

Composite video
– Convert RGB to YIQ (YUV)
– Multiplexing YIQ into a single signal
– Used in most consumer analog video devices



S-video
– Y and C (QAM of I and Q) are stored separately
– Used in high end consumer video devices



High end monitors can take input from all three

© Yao Wang, 2004

Video Basics

72

Homework
• Reading assignment:
– Chap. 1.

• Problems:









Prob. 1.5.
Prob. 1.6.
Prob. 1.7.
Prob. 1.8.
Prob. 1.9.
Prob. 1.10
Prob. 1.11
Prove mux/demux with QAM will get back the original two signals © Yao Wang, 2004

Video Basics

73…...

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