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2. c C www.deenemubeen.com 3. 2 4. 1 1 http://www.deenemubeen.com/ 5. 3 m ll m m m 2ll 2 http://www.deenemubeen.com/ 6. 4 http://www.deenemubeen.com/ 7. 5 3 8. 9. m m 4ll 3 4 http://www.deenemubeen.com/ 10. 6 m m ll http://www.deenemubeen.com/ 11. 7 12. 13. m m ll http://www.deenemubeen.com/ 14. 8 ll m m Video Recording, process of recording still or moving images electronically,rather than photochemically as in photographic film. The techniques used torecord images on videotape are similar to those used to record sound (see SoundRecording and Reproduction). Electrical signals from a television camera (orfrom a television camera via a television receiver) are stored as patterns ofmagnetized regions of iron oxide on so-called magnetic tape. When the recordedtape is played back, the original signals are generated. These signals can then bedisseminated by broadcast antenna or by cable to television receivers thattranslate the signals into images and sounds..Microsoft Encarta Reference Library 2003. 1993-2002 MicrosoftCorporation m 15. m 16. 17. ll http://www.deenemubeen.com/ 18. 9 IIITHE TELEVISION CAMERAThe television camera is the first tool used to produce a television program. Mostcameras have three basic elements: an optical system for capturing an image, apickup device for translating the image into electronic signals, and an encoder forencoding signals so they may be transmitted.AOptical SystemThe optical system of a television camera includes a fixed lens that is used tofocus the scene onto the front of the pickup device. Color cameras also have asystem of prisms and mirrors that separate incoming light from a scene into thethree primary colors: red, green, and blue. Each beam of light is then directed toits own pickup device. Almost any color can be reproduced by combining thesecolors in the appropriate proportions. Most inexpensive consumer video camerasuse a filter that breaks light from an image into the three primary colors.BPickup DeviceThe pickup device takes light from a scene and translates it into electronicsignals. The first pickup devices used in cameras were camera tubes. The firstcamera tube used in television was the iconoscope. Invented in the 1920s, itneeded a great deal of light to produce a signal, so it was impractical to use in alow-light setting, such as an outdoor evening scene. The image-orthicon tubeand the vidicon tube were invented in the 1940s and were a vast improvement onthe iconoscope. They needed only about as much light to record a scene as humaneyes need to see. Instead of camera tubes, most modern cameras now use light-sensitive integrated circuits (tiny, electronic devices) called charge-coupleddevices (CCDs).http://www.deenemubeen.com/ 19. 10 When recording television images, the pickup device replaces the function of filmused in making movies. In a camera tube pickup device, the front of the tubecontains a layer of photosensitive material called a target. In the image-orthicontube, the target material is photoemissive-that is, it emits electrons when it isstruck by light. In the vidicon camera tube, the target material isphotoconductive-that is, it conducts electricity when it is struck by light. In bothcases, the lens of a camera focuses light from a scene onto the front of the cameratube, and this light causes changes in the target material. The light image istransformed into an electronic image, which can then be read from the back of thetarget by a beam of electrons (tiny, negatively charged particles).The beam of electrons is produced by an electron gun at the back of the cameratube. The beam is controlled by a system of electromagnets that make the beamsystematically scan the target material. Whenever the electron beam hits thebright parts of the electronic image on the target material, the tube emits a highvoltage, and when the beam hits a dark part of the image, the tube emits a lowvoltage. This varying voltage is the electronic television signal.A charge-coupled device (CCD) can be much smaller than a camera tube and ismuch more durable. As a result, cameras with CCDs are more compact andportable than those using a camera tube. The image they create is less vulnerableto distortion and is therefore clearer. In a CCD, the light from a scene strikes anarray of photodiodes arranged on a silicon chip. Photodiodes are devices thatconduct electricity when they are struck by light; they send this electricity to tinycapacitors. The capacitors store the electrical charge, with the amount of chargehttp://www.deenemubeen.com/ 20. 11 stored depending on the strength of the light that struck the photodiode. The CCDconverts the incoming light from the scene into an electrical signal by releasingthe charges from the photodiodes in an order that follows the scanning patternthat the receiver will follow in re-creating the image.CEncoderIn color television, the signals from the three camera tubes or charge-coupleddevices are first amplified, then sent to the encoder before leaving the camera.The encoder combines the three signals into a single electronic signal thatcontains the brightness information of the colors (luminance). It then addsanother signal that contains the code used to combine the colors (color burst), andthe synchronization information used to direct the television receiver to followthe same scanning pattern as the camera. The color television receiver uses thecolor burst part of the signal to separate the three colors again.IV SCANNINGTelevision cameras and television receivers use a procedure called scanning torecord visual images and re-create them on a television screen. The televisioncamera records an image, such as a scene in a television show, by breaking it upinto a series of lines and scanning over each line with the beam or beams ofelectrons contained in the camera tube. The pattern is created in a CCD cameraby the array of photodiodes. One scan of an image produces one static picture,like a single frame in a film. The camera must scan a scene many times persecond to record a continuous image. In the television receiver, another electronbeam-or set of electron beams, in the case of color television-uses the signalshttp://www.deenemubeen.com/ 21. 12 recorded by the camera to reproduce the original image on the receivers screen.Just like the beam or beams in the camera, the electron beam in the receiver mustscan the screen many times per second to reproduce a continuous image.Microsoft Encarta Reference Library 2003. 1993-2002 Microsoft Corporation m m 22. (Optical System 23. 24. Lens 25. Prisms 26. Light 27. Scene 28. (Mirrors) Beam 29. 30. (Pickup Device 31. 32. (Electronic Signals) b http://www.deenemubeen.com/ 33. 13 (Light- CCDs) Sensitive Integrated Circuits) Photoconductive 34. 35. Electromagnets System 36. 37. Scan 38. CCD) Electronic Signals 39. Photodiodes 40. http://www.deenemubeen.com/ 41. 14 Photodiodes 42. (Encoder 43. 44. (Scanning) http://www.deenemubeen.com/ 45. 15 ll 46. m m 5 5 http://www.deenemubeen.com/ 47. 16 6 ll m m 48. m m 7 ll 49. 6 7 http://www.deenemubeen.com/ 50. 17 8 m m 9 ll 8 9 http://www.deenemubeen.com/ 51. 18 m m 52. 53. 54. 55. 10 ll 56. 10 http://www.deenemubeen.com/ 57. 19 Security 58. 59. http://www.deenemubeen.com/ 60. 20 61. m ll m http://www.deenemubeen.com/ 62. 21 http://www.deenemubeen.com/ 63. 22 m m 64. 11ll 11 http://www.deenemubeen.com/ 65. 23 m m 12 66. m m 12 http://www.deenemubeen.com/ 67. 24 13 13 http://www.deenemubeen.com/