COLOR SIGNAL TRANSMISSION AND RECEPTION

PPT INCLUDES COLOR SIGNAL TRANSMISSION AND RECEPTION DETAILS ,CAMERA ,COLOR PICTURE TUBE AND ITS TYPES ,COLOR TV CAMERA

1. Chapter 2 Color signal transmission and reception SUBJECT:VIDEO ENGINEERING By-Miss S U. Revankar Assistant Professor, Dept. of E & TCE, SITCOE,Yadrav,Ichalkaranji

2. Color t.v camera

3. It essentially consists of three camera tubes in which each tube receives selectively filtered primary colors . Each camera tube develops a signal voltage proportional to the respective color intensity received by it. Light from the scene is processed by the objective lens system. The image formed by the lens is split into three images by means of glass prisms . These prisms are designed as diachroic mirrors.

4. A diachroic mirror passes one wavelength and rejects other wavelengths (colors of light). Thus red, green, and blue color images are formed. The rays from each of the light splitters also pass through color filters called trimming filters .  These filters provide highly precise primary color images which are converted into video signals by image-orthicon or vidicon camera tubes .

5. Thus the three color signals are generated . These are called Red (R), Green (G) and Blue (B) signals Simultaneous scanning of the three camera tubes is accomplished by a master deflection oscillator and sync generator which drives all the three tubes.  

6. The three video signals produced by the camera represent three primaries of the color diagram. By selective use of these signals, all colors in the visible spectrum can be reproduced on the screen of a special (color) picture tube.

7. COLOR PICTURE TUBE: Delta Gun Color Picture Tube Gun-in-Line or Precision-in-line Color Picture Tube Single gun or Trinitron Color Picture Tube

8. Delta gun color picture tube

9. Radio Corporation of America RCA 3 separate guns for 3 colours. Guns equally spaced at 120 ,tilted towards axis. Screen coated with 3 different phosphors for R, G, B. Triad contains 1 dot of each colour . 3,33,000 triads. Eye integrates 3 colour information to give a sensation of combined hue. Shadow mask. One hole per triad. All stray electrons (80%) get collected by mask.

10. Disadvantage of Delta gun tube: Convergence is difficult. Very elaborate arrangements to overcome it. Focus not sharp over entire screen. Mask passes only 20% of electrons.

11. Precision in line color picture tube

12. 3 Guns in line simplifies convergence adjustment. Colour phosphors in form of vertical stripes. Distance same as in Delta gun. More efficient . Larger % of electrons pass through mask . Fewer convergence adjustments. Most widely used.

13. Trinitron picture tube

14. By Sony Corporation, Japan Single gun having three cathodes. Simplified construction as only one electron assembly. Three phosphor triads arranged in vertical strips. Each strip is few thousandth of a cm. A metal aperture grill has one slot each triad.  Grill has greater electron transparency. Three beams appear to emerge from same point.

15. Purity and covergence PURITY:

16. Each beam must fall at center of corresponding dot. Irrespective of position of triad on screen. Circular magnets called purity magnets on neck of yoke does the alignment. If all tabs moved together, they change direction of field. If tabs are separated, magnetic field reduces . 2, 4, 6 pole magnets to achieve collective or individual beam deflection. Error may also occur if yoke is not positioned properly.

17. CONVERGENCE :

18. Technique that all electrons hit the same part of the screen to produce 3 coincidental rasters . C onvergence occurs due to Errors – Non-coincidental convergence plane. Non-uniformity of deflection field. Flat surface of picture tube screen.

19. Proper convergence is achieved by positional adjustment of the individual beams. It falls into two parts referred to as (i) static and (ii) dynamic convergence Static and dynamic convergence. Static convergence by permanent magnet. Once correctly set, brings the beam into convergence in the central area of the screen Dynamic convergence converges beam over rest of the screen.

20. Degaussing Due to Earth magnetic field and other nearby magnetic fields, mask and mounting frame may get magnetized. Will cause purity error causing in colour patches. Can be repaired by influencing the screen by an alternating magnetic field which gradually reduces to zero.

21. Automatic degaussing

22. At switch ON, thermistor is cold and has high resistance. More AC passes through coil and varistor , causing alternating magnetic field. Thermistor gradually heats up, reducing its resistance . More current flows through thermistor. Lesser current through coil and varistor . Heats thermistor further •.

23. This continues till current through thermistor becomes maximum. Current through varistor and coil gradually reduces to zero. Components chosen to give initial surge of 4ampere to D.Coil . Final current less than 25mA in less than a second

24. COLOR MIXING THEORY Additive color mixing theory Subtractive color mixing theory

25. ADDITIVE COLOR MIXING THEORY

26. Additive color mixing theory deals with mixing of  light . The primary colors red, blue and green can be paired to form white (red, blue and green), magenta (red and blue), yellow (red and green) and cyan (green and blue).

27. Subtractive color mixing theory

28. Subtractive color mixing theory deals with  pigments or dyes  with three primary colors magenta, yellow and cyan - which can be mixed together to form colors in the visible light spectrum. By mixing the primaries the subtractive secondaries black (magenta, yellow and cyan), red (magenta and yellow), blue (magenta and cyan) and green (cyan and yellow) can be made

29. Characteristics of color There are three qualities which are used to describe  any one color.   These are hue, saturation, and brightness . HUE: Hue is a quality which is used to identify any color under consideration, such as red, blue, or yellow. A hue is a pure color that has not been shaded with black or tinted with white. SHADE: A hue mixed with black TINT: A hue mixed with white TONE: A hue mixed with both black and white

30. SATURATION : Saturation , also called " chroma ," is a measure of the purity of a color or how sharp or dull the color appears. BRIGHTNESS : Brightness , also called "luminance" or "value," is the shade (darkness) or tint (lightness) of a color. Areas of an evenly colored object in direct light have higher brightness than areas in shadow .

31. Chromaticity diagram What is chromaticity the quality of a color as determined by its dominant wavelength and its purity . Chromaticity diagram is a convenient space coordinate representation of all the spectral colors and their mixtures.

32. NTSC color tv system NTSC  (National Television Standards Committee) is the oldest existing standard, developed in the USA and first used in 1954. It's parameters are as follows: Lines: 625 Frame rate: 29.97 Hz Picture resolutions: 720 x 480; 704 x 480; 352 x 480; 352 x 240 The Countries that support NTSC video are as follows: Antilles, Netherlands, Bahamas, Barbados, Belize, Bermuda, Bolivia, Burma, Canada, Chile, Columbia, Costa Rica, Cuba, Dominican Republic, El Salvador, Ecuador, Grenada, Guatemala, Honduras, Jamaica, Japan, Mexico, Panama, Peru, Philippines, Puerto Rico, South Korea, Surinam, Taiwan, Tobago, Trinidad, United States of America, Venezuela .

33. NTSC transmitter diagram

34. NTSC receiver

35. PAL COLOR TV SYSTEM PAL  (Phase Alternating Line) was developed in 1967 by the United Kingdom & Germany. PAL standard utilizes a wider channel bandwidth than NTSC which allows for better picture quality. It's Parameters are as follows: Lines: 525 Frame rate: 25 Hz Picture resolution: 720 x 576; 704 x 576; 352 x 576; 352 x 288 The countries that support PAL are as follows: Algeria, Andorra, Angola, Argentina, Australia, Austria, Bahrain, Bangladesh, Belgium, Botswana, Brazil, Brunei, Cameroon, China, Denmark, Ethiopia, Fiji, Finland, Germany, Ghana, Gibraltar, Hong Kong, Iceland, India, Indonesia, Ireland, Israel, Italy, Jordan, Kenya, Kuwait, Lesotho, Liberia, Luxemburg, Malawi, Malaysia, Maldives, Malta, Mozambique, Namibia, Netherlands, New Zealand, Nigeria, Norway, Oman, Pakistan, Papua New Guinea, Paraguay, Portugal, Qatar, Rumania, Seychelles, Sierra Leone, Singapore, Somalia, South Africa, Spain, Sri Lanka, Sudan, Swaziland, Sweden, Switzerland, Syria, Tanzania, Thailand, Turkey, Uganda, United Arab Emirates, United Kingdom, Uruguay, Yemen, Yugoslavia, Zambia, Zimbabwe

36. PAL ENCODER

37. PAL DECODER

38. SECAM COLOUR TV SYSTEM SECAM  ( Squentiel couleurmmoire ) was developed in France in 1967. SECAM uses the same bandwidth and resolution (720x576) as PAL but transmits the color information sequentially. Take note that only a handful of products support SECAM.  The countries that support SECAM are as follows: Afghanistan, Benin, Burkina Faso, Bulgaria, Burundi, Central African Republic, Chad, Congo, Czechoslovakia, Djibouti, Egypt, France, French Guiana, Gabon, Greece, Guadalupe, Guinea, Gyprus , Haiti, Hungary, Iran, Iraq, Ivory Coast, Lebanon, Libya, Madagascar, Mali, Martinique, Mauritius, Mauritania, Monaco, Morocco, Niger, North Korea, Poland, Russia, Rwanda, Saudi Arabia, Senegal, Syria , Togo, Tunisia, Vietnam, Western Samoa, Zaire.

39. SECAM ENCODER

40. SECAM DECODER

41. Difference between ntsc pal and secam

42. Compatibility consideration

43. Energy bundle

44. Frequency interleaving process interleaving of c olor signal

45. Interleaving of energy b undle

46. Video signal band bears a definite relation with scanning frequencies.  Energy content of video signal is contained in individual energy “bundles”.  Bundles occur at harmonics of line frequency.15625Hz  Components of each bundle separated by multiple of field frequency. 50, 100, 150… 

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