Basics of Colour Television and Digital TV

Main characteristics of human eye with regard to perception of colours-mixing of colours. three standards of colour transmission system, CATV, DTH, HDTV & SMART TV
For TS-SBTET, C-18, DECE 6 Unit, By Nenavath Ravi Kumar, MIST Hyderabad

1. Microwave Communications and Television DECE, II Year-IV Semester Nenavath Ravi Kumar Associate Professor ECE Dept-MIST

2. Unit-6 Basics of Colour Television and Digital TV

3. INTRODUCTION TO COLOUR TV The first commercial colour TV started in US in 1954 The main constraint for the design of color TV was maintaining compatibility with existing monochrome TV Compatibility: Colour TV signal must produce normal monochrome picture on monochrome TV Reverse Compatibility: Monochrome signal must produce a normal monochrome picture on colour TV

4. INTRODUCTION TO COLOUR TV Requirement for achieving compatibility: Colour TV signal should occupy the same BW Location of picture and sound carriers should be the same The colour signal should have the same luminance (brightness) information as B&W TV The composite colour signal should contain colour information and other ancillary signals The colour information should not not affect the picture reproduced on the screen of a monochrome receiver. The system must use the same deflection frequencies.

5. Concept of color What is color? Color is the light wavelengths that the human eye receives and processes from a reflected source. When light shines on an object some colors bounce off the object and others are absorbed by it. Our eyes only see the colors that are bounced off or reflected. How do we see color? The inner surfaces of our eyes contain photoreceptors—specialized cells that are sensitive to light and relay messages to our brain. There are two types of photoreceptors: cones (which are sensitive to color) and rods (which are more sensitive to intensity). We are able to “see” an object when light from the object enters our eyes and strikes these photoreceptors. Light with a wavelength of about 400 nm is seen as violet, and light with a wavelength of about 700 nm is seen as red.

6. COLOUR PERCEPTION All colours are perceived by human eye by the stimulation of the three groups of the cones at different levels The sensitivity of human eye is maximum for green light (550nm)

7. C O L O U R MIXING Subtractive Mixing The combination of two colours reflects only the colours which are common to both Uses the reflective property of the pigments Used in painting and printing Additive Mixing Light from 2 or more colours obtained either from independent sources or through filters can create a combined sensation of a different colour Used in TV systems

8. C O L O U R mixing Additive mixing Subtractive mixing

9. Complimentary colours The colours which are obtained by pair wise additive mixing of primary colours are know as complimentary colours Red + Green = Yellow Red + Blue = Magenta Blue + Green = Cyan

10. TRISTIMULUS VALUES The values of the individual colour components to get a particular colour is known as the tristimulus values The wavelengths of red (700nm), green(546.1nm) and blue(438.8nm) are standardized to make different colours by additive mixing The relative strengths of these components for getting different colours also have been standardized E.g. white= 30% red + 59% green + 11% blue i.e. 1 lumen white= 0.3 lumen red+0.59 lumen green + 0.11 lumen blue

11. Luminance, Hue & Saturation Luminance (Brightness): Amount of light intensity perceived by the eye regardless of the colour Hue (tint): This is the spectral colour of the light - Different hue due to different wavelengths and perceived by the cones of the retina - Eg : red apple is red due to red hue Saturation: Spectral purity of the colour . - Saturation indicates whether a colour is diluted (by mixing with white) or not. - Saturation 100% means no white component Hue and saturation put together is known as Chrominance

12. Chrominance signal Chrominance signal contains all the colour information. It indicates both the hue & saturation of colour. Chrominance signal is also called the c-signal Chrominance signal obtained from the colour difference signals R-Y & B-Y, a colour difference signal can be produced by adding the Y signal with its phase reverse –Y to any of the signals R,B or G of the three possible colours difference signal, R-Y, B-Y & G-Y.

13. Production of color difference signal Voltage Vy is low because Rc is chosen to be small to avoid crosstalk. Hence it is amplified before it leaves camera subchassis. Also the amplified Y signal is inverted to obtain –Y signal Then two adder circuits to obtain (R-Y) and (B-Y)

14. Compatibility and reverse compatibility Colour television signal must produce a normal black & white picture on monochrome T.V receiver without any modification of the receiver circuitry. This is known as ‘ Compatibility’ A colour receiver must be able to produce a black & white picture from a normal monochrome signal. This is referred to as ‘ Reverse Compatibility ’

15. Compatibility and reverse compatibility The following requirements are needed for compatibility. The colour signal should occupy the same bandwidth as the monochrome The location and spacing of picture and sound carriers should be same as in monochrome signal. The colour system has to employ the same deflection frequencies and sync signals as the monochrome system. The channel bandwidth is also required to be same as the monochrome system.

16. Colour Transmission System Composite Video Signal Encoding the Chrominance over Luminance into one signal (saving bandwidth): NTSC (National TV System Committee) North America, Japan – PAL (Phased Alternation Line) Europe (Including Israel) – SECAM ( Systeme Electronique Color Avec Memoire) France, Russia and more

17. How chrominance signals are transmitted on one carrier in pal system The modulated picture sub-carrier containing the colour information is to be accommodated in the standard TV channel bandwidth(7MHz). This channel width is already fully occupied by the luminance signal which has bandwidth of 5MHz. This problem is solved by employing a method is known as frequency interleaving . frequency interleaving is the process of accommodating colour information signals between the vacant spaces of clusters.

18. Each cluster consists of harmonics of line frequencies (H, 2H,3H, 4H......NH) i.e. 1Hz=1x15625 = 15625Hz 2Hz=2x15625 = 15625Hz 3Hz=3x15625 = 15625Hz 4Hz=4x15625 = 15625Hz .. .. .. 320Hz=320x15625 = 5MHz

19. Frequency Interleaving The colour signal is interleaved in these gaps The carrier frequency is so chosen that its sideband frequencies fall exactly mid-way between the harmonics of the line frequency. This requires that the frequency of the subcarrier must be an odd multiple of half the line frequency. i.e. (2n+1)* 15625/2 In 625 line system, this freq. is selected as 4.43MHz (2*283+1)*15625/2 In 525 line system it is 3.58MHz

20. Frequency Interleaving

21. Block diagram of colour tv transmitter C Signal 1 2

22. Block diagram of colour tv transmitter Colour camera : The scene to be televised is separated into R,G & B. Colour matrix : Separate luminance signal (Y) & chrominance signals (R-Y & B-Y) using suitable matrix. LPF: Limits chrominance signals bandwidth 1.5MHz. Modulators : Chrominance signals are Amplitude modulated by colour subcarrier signals of 6.8MHz. Colour subcarrier generator : Generates 4.43MHz. Adder : Adder 2 adds both chrominance modulated signals it is C-signal and Adder 1 adds C-signal and Y-signal is the composite colour video signal. Main transmitter : Using antenna radiates Colour video signal and Audio signal into space.

23. Block diagram of colour tv receiver

24. Block diagram of colour tv receiver RF Tuner : Selects only band TV signals. Video IF Amplifier : To boost received TV signals Video detector & Video Amplifier : To detects Video signal and separate C-signal, Y-signal & sync signal Audio & Video Signal. Detector : Amplitude demodulation of Chrominance signals. Colour subcarrier generator : Generates 4.43MHz. Phase reverse switch : 90 degrees phase shift. Matrix : To generate (R-Y), (G-Y), and (B-Y) from chrominance signals (R-Y & B-Y) . Matrix 1 : (R-Y), (G-Y), and (B-Y) colour difference signals are added with Y-signal in the matrix and generates R,G & B signals fed to tri colour picture tube. Sync pulse : pulses are separated and fed to vertical & horizontal deflection circuits to deflect to electron beam.

25. Processing of colour video signal (PAL- system)-PAL-Decoder U+jV U+jV U- jV

26. Processing of colour video signal (PAL- system)-PAL-Decoder The received signal from Rx Antenna fed to Video detector ( Chroma Signala ). The output of Video detector connected Y-Amplifier & BPF of 3-5 MHz. The problem of cross interference (distortion) between U and V signals in the video detector’s output is solved by using delay circuit of 64us before U&V signals. At the added & subtraction we get Assume U+jV Direct signal U- jV Delay Line signal The j operator with V-signal indicates that V is at 90 degree phase difference with U-signal. Adding two expressions to get 2U signal at the added output i.e U+jV+U-jV =2U Subtraction of expressions to get 2jV signal at the added output i.e U+jV -U-JV= 2jV . These U & V signals are added in the matrix to produce R-Y, G-Y & B-Y signals. These three colour signals and Y-signal is added in the RGB matrix to produce R, G & B colours.

27. PAL-Decoder Advantages  : -The phase error causing error in reproduction of colour is eliminated -Bandwidth of U & V is same .This simplifies filtering action -Studio mixing is easy as compared to SECAM -Use of delay lines before demodulators isolates U and V signal s from each other reduces crosstalk type of interference in colours better than NTSC-results in better picture quality Disadvantages: -Electronic circuit and Ident signals are necessary in PAL which makes the design complex -Delay line technique reduces vertical resolution of chroma signal

28. Processing of colour video signal (PAL- system)-PAL-Encoder

29. Processing of colour video signal (PAL- system) -Encoder The R, G & B signal for the camera are combined in the Y-matrix to form Y-signal. The U-V matrix combines the R&B signal with –Y signal to obtain U & V signals. The colour subcarrier is modulated in the quadreture by the U & V Signal. The colour subcarrier is fed to the U modulator over a 90 degree phase shift network while the V modulator gets the subcarrier over a 0 to 180 phase shift switched in every alternate line by electronic commutator . Two modulated chrominance signal U & ± jV signal are combined in the adder stage and the F-signal is obtained.

30. cable tv system Introduction to cable TV Basically cable TV system is classified as MATV(master antenna TV) CCTV(close circuit TV) CATV(cable TV) Cable TV was initially introduce for the benefit is possible of communication in rural area that were beyond the range of broadcast transmission However with the advent of satellite television, reception of signal from a large number of TV station located far away become possible. With this cable TV developed in a complex multi channel system and expanded in a big way in all countries.

31. cable tv system Cable sig . nal resources The first step in cable TV is to collect the desired signal from available source. The main signal coming from various satellite. for that purpose high gain antenna is required. By correct adjustment of this antenna towards satellite, collect signal arriving from it by dish and deliver these to LNBC. this minimize the losses in co axial cable. Principle : The parabolic reflector antenna collects all the electromagnetic waves from satellite due to parabolic shape reflected rays concentrated at focal point which give the high gain signal.

32. cable tv system Specification of Dish Antenna: Size - 8feet. Gin - 36db. Band –c (3.7 to 4.2GHz downlink frequency) Look angle - 360 rotation in azimuth. Offset angle - 24.62limit Focal length - 90cm Azimuth angle= 0 to 360 Aperture efficiency -75%

33. Simple block diagram of cable tv system

34. diagram of cable tv system function Head-end : Broadcast signals are received from the various satellite by using antennas. They are amplified by a low noise amplifier (LNA). Trunk Lines : Trunk lines are coaxial cables are used to provide the high bandwidth low noise. Trunk Amplifiers : Trunk amplifiers are used between trunk lines (coaxial cables) to compensate for signal loss in cables and to increase the distance of the signal without losses. Signal Splitters : Signal splitters are also directional couplers. This can be used to distribute cable signal from trunk lines to ranch routes. The Branch Line Cable : The branch line comes out of the main trunk line. It is also Bridge Amplifier : The bridge amplifier to act as bridge between trunk line and the branch line. Care of impedance matching. Drop Line : It is the from branch line to subscriber home TV. Line Extension Amplifiers : When branch line is to be extended a line extension amplifier becomes necessary to amplify signals and hence it is called line extender

35. Need of satellite for dth CA TV system uses coaxial cable for connecting the television sets to the head end so the cost of system increases with distance of consumers from the head end. Signal strength decreases with increasing distance which requires amplifiers for specified distance which again increase the cost of the system Illegible tapings are possible along the coaxial cable. CA TV systems are not able to provide services in remote areas such as forests, hilly regions, rural areas etc. Early satellite television was broadcast in C-band - radio in the 3.4 gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (10 GHz to 14 GHz ). Doordarshan TV is India's biggest broadcast with over 1400 territories and covering approximately 90% of geographical area.

36. Components of DTH The major components of DTH are Satellites Signal Processing (Broadcasting centre, Multiplexers, Modulators) DTH Antenna LNB Set-top Box Schematic Picture of DTH :

37. Satellite A Geo-Stationary satellite plays an important role in DTH systems. Satellites are higher in the sky than TV antennas, so they have a much larger "line of sight" range. The television satellites are all in geosynchronous orbit, meaning that they stay in one place in the sky relative to the Earth . In India DD Direct & Dish TV transmission services are from NSS-6 Satellite . Specifications of NSS-6 Satellite : • Location : 95 degree East • No. of Ku-Band Transponders : 60 • Ku Band Uplink : 13.75 to 14.5 GHz • Ku Band Down link : 10.95 to 11.70 GHz • Modulation Type : QPSK • Symbol Rate : 27.5 Mb/s. • Downlink for DD Direct : 12815, 12534, 12898 GHz. • Altitude = 57.26 degree

38. Broadcast Centre: The provider doesn't create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between you and the actual programming sources. The broadcast centre is the central hub of the system. The satellites receive the signals from the broadcast station and rebroadcast them to the ground. The viewer's dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer's house. The receiver processes the signal and passes it on to a standard television . With MPEG-2 compression, the provider can reduce the 270- Mbps stream to about 5 or 10 Mbps (depending on the type of programming ). With digital compression, a typical satellite can transmit about 200 channels.

39. Multiplexer & Modulator A multiplexer is a device which transmits the information of many channels in one channel . The multiplexer is built in the broadcasting centre . The multiplexer in the broadcasting centre compresses all the frequency signals into one single channel & transmits it to the GeoStationary satellite. It sends the single channel to the modulator . Modulation is a process in which the information signal is imposed on a carrier signal which is of high strength and greater frequency . This process is done in the modulator . The modulator modulates the signals and sends to the encoder

40. DTH Antenna The reflector's surface material must be constructed out of metal in order to reflect the incoming microwave signals. Some antenna reflectors appear to be manufactured out of plastic or fibre glass; however, these dishes actually have an embedded metal mesh material that reflects the incoming satellite signals to the front and centre of the dish. Dish Antenna

41. LNB (Low Noise Block Down Converter): The incoming satellite signal propagates down the waveguide of the feed horn and exits into a rectangular chamber mounted at the front of the low-noise block down converter (LNB), in which a tiny resonant probe is located. This pickup probe, which has a wavelength that resonates with the incoming microwave frequencies, conducts the signal onto the first stage of electronic amplification. A wide band product called a "universal" Ku-band LNB is available that can switch electronically between the 10.7-11.7 and 11.7-12.75 GHz frequency spectra to provide complete coverage of the entire Ku-band frequency range.

42. Set-Top Box: The set top box accepts the entire down converted band and separates out the individual transponder frequency . Then signals are first converted to fixed IF and then QPSK demodulated . The bandwidth of QPSK signals is 27.5 MHz as the bit rate is 27.5 Mb/s . It is observed that 11 digital channels are multiplexed in 27.5 MHz bandwidth . After the QPSK demodulation, the digital bit stream obtained contains several multiplexed channels as well as error control bits . The bit stream is processed to correct and detect errors, deinterleaved , and decrypted . A digital demultiplexer then extracts the bits for wanted channel, and sends them to MPEG decoder, and finally generates analog Audio and Video signals with DIA converters to drive TV set.

43. Deficiencies in existing tv system Present TV signals can’t project the vivid (pure) impressions and emotions as the 35mm. Line visibility when brightness is high. Unpleasant when the viewer is close to the screen. Narrow aspect ratio of 4:3 and small screen size permits the small viewing angle of around 15 degrees. Peripheral vision is not involved in viewing the picture. Need not to move the eyes or head to the follow the action

44. How does . DTH differ from Cable TV In DTH channel should be transmitted from the satellite to a small dish antenna mounted on the window or roof top of the user house So the broadcast directly contact to the user . The middle man like cable operator are not there in picture . Also with DTH a user can see nearly 700 channels. DTH offer better quality picture than cable TV . This is because cable TV in India is analog . DTH offer stereophonic sound effect. It can also reach remote terrestrial area where transmission and cable TV have filed to penetrate.

45. High definition tv ( hdtv ) Is a digital television broadcasting system. HDTV is simply the highest of all the DTV standards HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used. pictures look so much sharper and clearer than regular TV. HD get its clarity from a feature called Resolution. Resolution means the amount of visual information in a picture. The number of pixels which gives resolution. A pixel is a tiny square or rectangle . Each pixel creates one tiny dot of colour . Many pixels combine to form an image on screen. Higher Pixels equals higher resolution and a better picture

46. High definition tv ( hdtv ) HDTV aims at : Improvement in both vertical and horizontal resolution of reproduced picture by approximately 2:1 over existing standard. Much improved color reproduction Higher aspect ratio of at least 5:3 Stereophonic sound. Development of HDTV Pioneer-NHK, Japan Broadcasting corporation Tokyo Standard adopted include 1125 scanning lines per frame, 60 fields per second,2:1 interlace scan and aspect ratio 16:9. Compatible to Europe’s 625 line PAL standard and America’s 525 line NTSC standard . MUSE stands for Multiple Sub- Nyquist Sampling Encoding and is an HDTV bandwidth compression scheme developed by NHK. Europe developed their own project named EUREKA compatible with CCIR standard but line number equal to 1249 and aspect ratio 16:9

47. Standard of hdtv 1125/60/2:1 Interlace System Number of scanning lines:1125 No of active lines:1035 Aspect ratio: 16:9 Scanning : 2:1 Interlace Field frequency : 60 Hz Samples for active lines: 960 for colour different 1920 for lumirances 1250/50/1:1 Progressive Scanning: Number of scanning lines:1250 No of active lines:1152 Aspect ratio: 16:9 Scanning :1:1 Interlace Field frequency : 50 Hz

48. Smart tv Smart TV sometimes referred to as connected TV or Hybrid TV Smart TV either have an ethernet port or Wi-Fi capability so we can stay connected to internet. In smart TV, the operating system is preloaded or available through set-top box

49. Features of smart TV Internet: High Quality Crystal Clear Picture: Miracast : Sharing Photos & Videos: High Resolution Videos: 4X Graphics Engine: Advanced Image Quality Enhancement Technology Experience dbx Surround S ound High Apect Ratio

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