Internet Engineering Dr. Marek Woda Multimedia and Computer Visualisation Part 3 Digital television (DTV) Lecture Overview • Several facts with history of television • Analog television (black & white) • Analog television (color) • Digital television Important facts • Etymology of Television (greek tele - far and latatin visio - the image seen) • Image transmission (analog TV) – line by line • „Phi phenomenon” - Max Wertheimer, 1912 • Signal value at a given moment = brightness of the point at the same time • TV Band = 6.5 / 5.5 MHz, which gives a about 800 points per line. • Flicker free - the first only the even lines and the odd ones are broadcasted one after the other 1. History of television • 1877 - Julian Ochorowicz, philosopher and psychologist, defined the general principles of television • 1897 - Ferdinand Braun, phisicist, presented the lamp, prototype of kinescope. • 1923 - Vladimir Zworykin constructs kinescope. • 1928 - Television signal becomes transmitted by Atlantic. USA - first station begins broadcasting regular program. • 1934 - "Prudential„ hotel, Warsaw, first experimental broadcast in Poland. • 1952 - USA, first recording of television signal. • 1953 - USA , NTSC standard, first standard of color television. • 1957 - France, SECAM standard. • 1961 - Germany, Walter Bruch defines PAL standard. • 1962 - first satelite (Telstar satelite) transmission from USA to Europe. • 1986 - stereo sound was introduced. • 1987 - USA, Japan, first digital television systems Television set „Wisła” - 1957 Power Supply: AC 110/127/220V Screen size: : 180x240mm Number of lines: 625 Bands (MHz): I - 49,75 - 56,25 MHz II - 59,25 - 65,75 MHz III - 77,25 - 83,75 MHz Loudspeakers: 2x0,5GD-2 lub 2x1-GD-5 a part of circuit diagram Price 4000 PLN Important facts • TV Signal comprises of • brightness (luminance) • color (chrominance) • synchronizing signals (mark the beginning of a new line and a new image) • sound • Standards: • NTSC (30 FPS, 525 Lines) • PAL, SECAM (25 FPS, 625 Lines) 2. Analog television (black & white) Image analysis – an image (two-dimensional) is converted to a signal (one- dimensional) in the time domain Signal transmission – a signal is transmitted from transmitter to receiver usually using electromagnetic waves Image reconstruction – in receiver, a signal is converted to an image, which be displayed on screen Image analysis – image conversion to one-dimensional signal (in the time domain ) An image is scanned by horizontal lines using interlace technique. line 1 line 0 odd lines line 3 line 2 line 5 line 4 line 7 line 6 line 9 line 8 parity lines line 11 line 10 Europe – 625 (576) lines, 25 frames per second. USA – 525 (496) lines, 30 frames per second TV luminance signal and spectrum U(f) an imge fh – horizontal scan rate … … fh 2fh 3fh 4fh (n-1)fh nfh (n+1)fh f Luminance signal spectrum Image reconstruction - CRT display horizontal and vertical dot scan signals anode u (t) u (t) video signal h v u(t) fluorescent cathode electron beam screen grids Problems: deflection circuits - image geometry, - „gamma” correction Gamma correction • a nonlinear operation used to encode and decode luminance or tristimulus values in videos / still images In the common case of A = 1, inputs and outputs are typically in the range 0–1 • human sight - greater sensitivity to relative differences between darker tones than between lighter ones • not gamma-encoded images allocate too many bits or too much bandwidth to highlights that humans cannot differentiate • CRT displays, the light intensity varies nonlinearly with the electron-gun voltage - gamma compression fixes nonlinearity, output picture has the intended luminance Gamma correction Gamma encoded images store tones more efficiently Original Linearly encoded using only 32 levels (5 bits) Gamma Encoded Gamma correction Reference Tone Perceived as 50% as Bright by Eyes Detected as 50% as Bright by Camera http://www.cambridgeincolour.com/tutorials/gamma-correction.htm The way of the electron beam 1 uh(t), uv(t) 3 1 3 5 7 9 11 13 15 17 19 2 2 5 7 9 11 Tv t 13 odd lines 15 17 Th uh(t) horizontal deflaction signal 19 uv(t) vertical deflation signal Europe – 625 lines per frame, 25 frames per second Horizontal scan rate fh = 15625 Hz, vertical scan rate fv = 50 Hz Composite video signal (black & white) - luminance signal - blanking signal - synchronization signal - audio signal Composite video signal (one line of image) reference white line n line n+2 1.00 V luminance blanking signal ~ 4.5 μs reference black 0.35 V 0.30 V synchronising pulse (vertical deflaction) 0 V T = 64 μs ~ 12 μs Composite video signal for one frame vertical sync and vertical blanking pulses equalizing pulses horizontal sync pulses equalizing pulses odd lines (visible) parity lines (visible) one frame Television system • UHF or VHF frequency ranges (country dependent) • Channel – picture information (amplitude modulatio) on one frequency – sound (frequency modulation) at a frequency at a fixed offset (typically 4.5 to 6 MHz) from the picture signal TV signal brodcasting Video carrier generator U 0 sin 2p f w t ( U 0 + uw ( t ))sin 2p f w t u ( t ) w Modulator (AM) composite video signal amplifier, antenna u f ( t ) Modulator (FM) audio U 0 sin 2p ( f w + u f ( t ))t signal U 0 sin 2p f f t Audio carrier generator TV channel structure (Europe) next channel -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 MHz video carrier fw audio carrier ff Channel bandwidth – 8 MHz Bandwidth for video - 6 MHz TV channnels (part of the table) Channel video frequency audio frequency number MHz MHz 1 (R1) 49.75 56.25 2 (R2) 59.25 65.75 3 (R3) 77.25 83.75 4 (R4) 85.25 91.75 5 (R5) 93.25 99.75 6 (K06) 175.25 181.75 7 (K07) 183.25 189.75 8 (K08) 191.25 197.75 9 (K09) 199.25 205.75 10 (K10) 207.25 213.75 11 (K11) 215.25 221.75 12 (K12) 223.25 229.75 ... … … 3. Analog television (color) Problems: - Compatability between color and black&white systems, color signal should be visible on black&white TV sets - Limited bandwidth, additional information about color required extension of bandwidth. Solution: The specific method of coding the information about colour has been introduced. Conversion from RGB to luminance - chrominance color model (YUV) R Y G U converter B V transmission channel Y R U G converter V B luminance (Y) – gray scale image chrominance (U, V or I, Q) – additional information about color Conversion formulas PAL NTSC U = ( B-Y ) * 0,493 I = 0,168*R - 0,257*G - 0,321*B V = ( R-Y ) * 0,877 Q = 0,212*R - 0,528*G + 0,311*B and éY ù é 0.229 0.587 0.114 ùéRù êU ú = ê- 0.146 - 0.288 - 0.434úêGú ê ú ê úê ú ëêV ûú ëê 0.617 - 0.517 0.100 ûúëêBûú éY ù é 0.229 0.587 0.114 ùéRù ê I ú = ê- 0.168 - 0.257 - 0.321úêGú ê ú ê úê ú ëêQûú ëê 0.212 - 0.528 0.311 ûúëêBûú Bandwidth for chrominance signals can be limited. RGB NTSC PAL R Y Y 6.0 f MHz 4.5 f MHz 6.0 f MHz G I U 6.0 f MHz 2.0 f MHz 1.2 f MHz B Q V 6.0 f MHz 1.0 f MHz 1.2 f MHz 6+6+6+ = 18 MHz 4.5+2.0+1.0 = 7.5 MHz 6+1.2+1.2 = 8.4 MHz.