video basics ---major ref. from ch.5 of textbook 2lad.dsc.ufcg.edu.br/multimidia/intro.pdf · video...
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1@NTUEE DSP/IC Lab
Video Basics ---major ref. From Ch.5 of textbook 2
■ Introduction ---- video industry
■ Video Imaging ---- video scan, aspect ratio
■ Color and Composite & component systems
■ From Analog To Digital Video
■ Spatial Conversions ---- video formats
■ Temporal Conversions
■ Mixing And Keying
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Cable Network
DVB-S downstream(max 90 Mbps)DSS
DVB-C downstream(max 40 Mbps)OpenCable
1. Satellite( fast PSTN/ ISDN2. Cable Modem ( QPSK, TCP / IP � for PSTN/ ISDN modem3. SDSL / ADSL / VDSL …..
IEEE 1394 / USBEthernet 10 Mbps…..
Satellite
Interaction Channel
Home Connection
Terrestrial (Plug&Play , high-data-rate)
(1-way / 2-way)
DTV set
DVB-T/ ATSC
DSTB
Cable Modem
DirecPC/DirecDuo
Video Environments
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Service Provision
TCP / IP
DVB-TDVB-S
(high speed BB)DVB-C
(Cable Modem)
HFC(Full Service
Network)
POTS(xDSL access)
Residential LAN(IR, RF, Wired)
Hybrid Services
DSTB
Wireless Cable(MMDS)
Video Service Environments
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Applications of Digital Video
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Benefits of Digital Video
i) Open Architecture video systems, meaning the existence ofvideo at multiple spatial, temporal, and SNR resolutionswithin a single scalable bitstream
ii) Interactivityiii) Variable-rate transmission on demandiv) Easy software conversion from one standard to anotherv) Integration of various video applicationsvi) Editing capabilities, such as cutting and pasting, zooming
removal of noise and blurvii) Robustness to channel noise and ease of encryptionviii) …...
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Descrambler OSD
Transport
NTSC/PALEncoder
CPU
MPEG-2Video
TrafficController
MPEG-2Audio
Digital Decoder Chip
Tuner
Tuner
Tuner
Satellite
Cable
Terrestrial
QPSKDemod
QAMDemod
COFDMDemod
FEC
FEC
FEC
SDRAM
Flash/EPROM
SDRAM VCXO
P1394 IR Buffer& Amp RS232 IrDA Port Modem
V-SeriesSmart CardBuffer P1284 SCSI
I2C
RFModulator
SECAMEncoder(optional)
DACs+ Filters
L
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Switch
RGB or Y/Cand CVBS
Graphics
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Future Video Systems
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Microsoft; GI; S-A Group( IBM,Pioneer,PowerTV,Sun,Toshiba);Intel Group(Cisco,Netscape,NCI,Oracle,Thomson CE);Intel/NCI; Oracle/NCI/Netscape; Thomson CE/NCI; Cisco; Sony;Thomson Sun(OpenTV); Samsung; Pioneer Digital Technologies;ACTV/Sarnoff; IBM; Criterion Software; Lucent Technologies;SCM Microsystems; Zenith Electronics; Worldgate Communications;Texas Instruments; Wink Communications; Panasonic
OpenCable
MCNS-DOCSIS
PacketCable* the specs will establish a data packet network for interactive services(carry IP Internet traffic, telephony,video,teleconferencing)
*broadband Cable Modem (interoperability)
*next-generation digital STB(include MCNS CM)*Open architecture(RTOSs / APIs / microprocessors)*exiting open Internet specifications*'98.3 specified -- IEEE1394(1úÚ)
are moving Cable forward in the race to
provide consumer broadband services
3Com; 8x8; Ascend; Bay Networks; Cisco; eFusion; Ericsson;Fore Systems; IBM; Intel/Lucent Team; Inter-Tel; Linkon; MediatrixPeripherals; Motorola; NEC; Netspeak; Nortel; S-A; Siemens/Com21Team; Sony; Sun; Vienna
Vendors ParticipationTasks / ObjectsScheduleItem'96.7
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Follow�ADC,Bay Networks,3Com,Com21,Cisco,GI,Motorola,NEC,NetGame,Panasonic,Phasecom,S-A, Samsung,Sony, Terayon,Thomson CE,Toshiba……..
full 2-way ,IP capable networks
by the year 2000
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Video Imaging
Imaging: normal photography, X-rays, electronic documents,electronic still pictures, motion pictures, TV
Video: a sequence of still pictures of a scene taken atvarious subsequent intervals in time
Scanning: a form of sampling of a continuously varyingtwo-dimensional signal
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Video Resolution
Viewing Ratio (VR):VR = d /PH d= viewer’s distance from the screen
PH= picture height
Visible pixels = 3440 /VR Pixel (Pel) : the smallest detail that can be reproduced in a
picture is about the size of a picture element
Minimum Viewing Rates
System Line or pixels/PH VRNTSC television 483 7.2HDTV 1080 3.2Computer display 768 <4.5
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Refresh Rate and Flicker
Persistence of vision, causes the visual system responds slowly to rapid changes of illumination
Flicker: if the illumination varies cyclically at a low frequency, the eye may perceive an annoying effect
Refresh Rate:the light output of display devices decays after a short time, and thereforemust be refreshed periodically to maintain the effect of steady illumination
Display Refresh Rates
System Refresh rate (Hz) Environment VRNTSC television 60(59.94) Living room 7PAL television 50 Living room 7Computer display 72 Bright office 1-2Motion picture theater48 Dark room 5-10
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Video ImagingRaster Scan ----(Progressive)
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Video Imaging
Interlace Raster Scan---- it is the tradeoff of bandwidth, flicker, and resolution----- may cause flicker problems for text and graphics
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Image Aspect Ratio
IAR is defined as the ratio of picture width to heightIAR = w / h
PAR (pel aspect ratio) = IAR * vertical_size / horizontal_size : full screen display
where horizontal_size is the width of the image in terms of pelsand vertical_size is the height of the image in lines
ex. Display IAR = 4:3 Image size = 720 pels * 486 lines
PAR = 4/3 x 486/720 = 0.9
or IAR * display_vertical_size / display_horizontal_size : portion display
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Gamma Correction
Many TV cameras and all CRT-based displays have a nonlinear relationship between signal voltage and light intensity. B = c v r + b B: light intensity c: gain factor
b: cutoff (camera) or black level (CRT) light intensityr: 1 ~ 3.0
To avoid gamma correction circuitry inside millions of TV receivers, gamma correction is doneprior to transmission. Ex. Assuming the gamma of camera to be 1 and that of the display to be2.2, then the camera voltage is raised to a power of 1/2.2 = 0.45.
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Human visual system
■ The retina consists of receptors sensitive to light calledphotoreceptors connected by nerve cells. Photoreceptors: Rodsand Cones, rods are responsible for low light vision, while conesare responsible for details and color under normal conditions, asin daylight.
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Primary Colors
Trichromatic theory of color:17 century, the perception of any color can be represented by just three variables
Additive color system (video system): RGB“additive” means they reproduce colors by adding colored light sources
Subtractive color system (painting and printing):magenta, cyan, and yellow (incorrectly) by RBYmodify the light reflected from white paper by absorbing (subtracting) certain colors
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Component Color Video SystemComposite System
In order to transmit or broadcast the analog video over a signal channel, there is aneed for composite color system that combine the three color components into asingle signal
Component SystemIn color video system, the devices must deliver three components to control the lightsources of display.
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Composite Color System
1. Luminance and Color-difference ComponentsY= 0.299R + 0.587G + 0.114BCr=R-YCb=B-Y
2. NTSC (59.94hz, 525 lines)
Y= 0.299R + 0.587G + 0.114B R= 1.0Y + 0.956I + 0.621QI= 0.596R - 0.274G - 0.322B G= 1.0Y - 0.272I - 0.649QQ = 0.211R - 0.523G + 0.311B B= 1.0Y -1.106I + 1.703Q
3. PAL (50hz, 625 lines)Y= 0.299R + 0.587G + 0.114BU = 0.492 ( B - Y )V = 0.877 ( R - Y )
4. SECAM (50hz, 625 lines)Y= 0.299R + 0.587G + 0.114BDb = -0.450R - 0.833G + 1.333BDr = -1.333R + 1.116G - 0.217B
*all RGB are gamma corrected.
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Summary of parameters used in worldwide color TV standards
Parameter NTSC PAL SECAMField rate (Hz) 59.94 50 50Lines per frame 525 625 625Gamma 2.2 2.8 2.8Audio Carrier (MHz) 4.5 QAM FMColor Subcarrier (MHz) 3.57 4.43 4.25(U)4.4(V)Color modulation method QAM QAM FMLuminance bandwidth(MHz) 4.2 5.0,5.5 6.0Chrominance bandwidth(Mhz) 1.3(I)0.6(Q) 1.3 1.0
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From Analog To Digital Video
■ Prefiltering (call prefilter prior to sampling)➤ Reduce unwanted excessive frequency and noise in the signal by
region filtering
■ Sampling➤ Sampling theorem (sampling frequency for NTSC, PAL,
CCIR601??)
■ Quantization
■ PCM (Pulse Code Modulation) Coding
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Video Formats
Picture format Luminance pixels Luminance linesCCIR601(525) 480 720CCIR601(625) 576 720SQCIF 128 96QCIF 176 144CIF1 352 2884CIF 704 57616CIF 1408 1152HDTV2 720 1280HDTV3 1080 1920
1: Common Intermediate Format2: at frame rates of 24, 30, 60 Hz progressive3: at frame rates of 24, 30 Hz progressive and 30Hz interlaced
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Other Commercial Image Structures
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Digital Video System
CCIR 601:Consultative Committee for International Radio (CCIR)--> International Telecommunications Union (ITU)Recommendation BT.601
4:4:4 Full-bandwidth sampling of R, G, B components4:2:2 Full-bandwidth Y, 2:1 horizontally-subsampled R-Y(U), B-Y(V)
4:1:1 Full-bandwidth Y, 4:1 horizontally-subsampled R-Y(U), B-Y(V)
4:2:0 Full-bandwidth Y, 2:1 horizontally-subsampled and vertically-subsampled R-Y(U), B-Y(V)
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Choice of video sampling frequency for ITU-R Rec.BT.601
525/59.94 625/50n Frequency n Frequency Dif.842 13248250 848 13250000 1750848 13342656 854 13343750 1094852 13405593 858 13406250 657856 13468530 862 13468750 220858 13499999 864 13500000 1860 13531467 866 13531250 217864 13594404 870 13593750 654868 13657341 874 13656250 1091
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From Analog To Digital Video(cont.)
■ The 4:2:0 format
■ The 4:2:2 format
■ The 4:4:4 format
MPEG-2
MPEG-1
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luminance and chrominance samples in a 4:4:4 video frame
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luminance and chrominance samples in a 4:2:2 video frame
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Interlaced and progressive representation of a 4:2:2 frame
Look like 2x1 array
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Luminance and chrominance samples in a 4:2:0 video frame
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Interlaced and progressive representation of a 4:2:0 frame
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CCIR-601 4:2:2 video frame
Spatial Conversions
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SIF, SIF-1, HHR and CCIR-601 4:2:0 video formats
576 for 25 frames/sec
SIF:source input format SIF-I: SIF interlaceHHR:half horizontal resolution
288 for 25 frames/sec
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■ CCIR-601 4:2:2➤ -- CCIR-601 4:2:0
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Spatial Conversion (cont.)
■ CCIR-601 4:2:2 -- SIF➤ 7-tap decimation filter [-29, 0, 88, 138, 88, 0, -29]/256 and➤ 4-tap interpolation filter [-12, 140, 140, -12]256 applied horizontally
-->(352)
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Spatial Conversion (cont.)
■ CCIR-601 4:2:2 -- HHR
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Spatial Conversion (cont.)■ CCIR-601 4:2:0 -- SIF-I
➤ same horizontal fileter plus vertical subsampling with➤ [-4, 23, 109, 109, 23, -4]/256 filter and interpolation filter➤ [-2, 20, 110, 110, 20, -2]256
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Temporal Conversion■ Problems: 60 f/s video --> 72 progressive f/s monitor
24 f/s film --> 60 fields/s TV monitor 50 fields/s PAL --> 60 f/s NTSC ….all via MPEG-2
■ Interlaced to noninterlaced➤ 1. Line interpolation - [1/2, 1/2] interpolation filter applied between each pairs of
consecutive lines in each field➤ 2. Field merging - combines lines of two consecutive fields, not good for motion➤ 3. Frame based line interpolation - as follows
The case is from fieldrate to same frame rate,so called Deinterlacing orline-doubling
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Temporal Conversion (cont.)
■ Noninterlaced to interlaced: ex. 60 frames/s to 60 fields/s➤ 1. Line subsampling➤ 2. Line weighting with filter [1/4, 1/2, 1/4]
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Temporal Conversion (cont.)Field Rate Conversion
ex. Between NTSC and PAL
1. Convert 60 fields/s to 50 fields/s
i) Discardii) Temporal interpolationiii) Motion vector interpolation
2. Convert 50 fields/s to 60 fields/s
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Temporal Conversion (cont.)
■ Film And Interlaced Video Conversion➤ 24 frames/s => 60 fields/s -- 3:2 pull down
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Mixing And Keying
Mixing can be defined as the addition of two or more input videosignals, Video = α1Video1 + α2Video2 + … or
Video = α1Video1 + (1-α1 )Video2
Luma Keying (short for Luminance keying), a level of luminance signal is specified for the scene containing the
foreground such that all pels above that values are replaced by the corresponding pels of the scene containing the background.
k = 1 rh<rfg use backgroundk = 0 rfg<rl use foregroundk = (rfg - rl)/(rh - rl) else rl <= rfg <= rh use blended
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Chroma Keying
Chroma keying consists of substituting a background signal in place of the foreground signal based on some key color identified in the foreground video signal, known as “blue screen”.
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