Video Technology


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Video Technology

  1. 1. VIDEO TECHNOLOGY By Nestor S. Abrogena Video technology was first developed for cathode ray tube television systems, but several new technologies for video display devices have since been invented. Standards for television sets and computer monitors have tended to evolve independently, but advances in computer performance and digital television broadcasting and recording are producing some convergence. The basic image reproduction for film and video had its roots in still photography. Light and a photosensitive material are the elements of image reproduction. PRINCIPLES OF IMAGE REPRODUCTION 1. STILL CAMERA (e.g. 35mm camera) - with a still camera, light falling on the subject is gathered and focused by the lens on to a photosensitive surface (film) where a latent image is recorded. Through a chemical process, the image is developed from which a positive is printed in a photographic enlarger. 2. MOVING CAMERA (e.g. 16mm camera) - light falling on a subject is similarly gathered and focused by the lens on to the film. The recording of the movement is however shot in a constant speed of 24 fps (frames per second). The latent image in the film is also chemically processed from which a positive image is printed. The film is projected at the same speed of 24fps to give an illusion of the movement. • PERSISTENCE OF VISION – after the film is developed, these images, separated from each other by an instant of darkness, are projected on a screen. Since the eye retains images slightly longer than it is actually exposed to them, it tends to meld 2 successive images into one, creating a smooth transition between them (same principle with flipbooks in animation and video). • On both still and moving camera, the illuminated subject is recoded into a photosensitive material (film). The latent image in the film negative is chemically processed to produce a negative image from which a positive image is printed. MOVING CAMERA: FILM FORMAT FILM- 1890’S- 35mm used by Thomas Alva Edison “kinetograph” before: CELLULOSE NITRATE-BASED – highly flammable and becomes explosive as it deteriorates with age now: CELLULOSE ACETATE-BASED 1
  2. 2. Film Format – width of the film and size and shape of the image that is recorded. 16mm- 1920’s; ¼ frame of 35mm - looks grainer and less sharp, but already coped due to technology SUPER 16- 1970’s; 16mm wide but 40% larger 8mm- 1932; ½ of 16mm SUPER 8- 1965; 8mm wide but 50% larger than 8mm - before the prime format of home movies LARGE FORMAT- 65mm / 70mm (added width for soundtrack) IMAX (image maximum) / ONIMAX- 65mm HORIZONTALLY ASPECT RATIO- width of the frame divided by the height 4:3 or 1.33:1- standard tv – picture is 4 units wide for every 3 units of height 16:9 or 1.85:1- Widescreen aspect ration used by American 1.66:1- European standard - Letterbox- cropping top and bottom 2.35:1- very wide screen (anamorphic) – when shooting, squeeze the width then unsqueezed in projection, widening original aspect ratio and restoring shapes to natural proportion. • RULE OF THUMB: the larger the format, the better the quality, the more expensive it is to shoot and the heavier the equipment to use 3. VIDEO CAMERA (the term “video is from latin word which means “I see”) - With a video camera, light illuminating the subject is gathered and focused by the vide camera lens. The incoming light is focused into a photosensitive surface and converted into an electrical signal. Bright areas cause more electric current to flow while dark areas cause less electric current to flow and its combination of light and dark lines makes up the video image. The video image is “scanned” or recorded into a metal particle impregnated tape. During, playback, the video signal of electrical fluctuation is converted back to light by a transducer (or a device, usually electrical or electromagnetic, that converts one type of energy or attributes to another for various purposes including measurement or information transfer we know as the television or video monitor. HOW DO VIDEO CAMERAS WORK? If you compare a still camera into a movie camera, once you take a shot, the camera shutter opens, and the image is instantly imprinted on the film. For each shutter opening, a single frame of film is exposed with the complete image of your subject. However, the video camera does not work in 2
  3. 3. the same manner. Since light is converted into an electrical signal, each frame of information doesn’t flow through the electrical cable at once. Since each tiny section of the picture has its own brightness level, which corresponds, to its own electrical level (value) the picture must be read and transmitted. An electron beam scans across the picture from one side to the other. The level of brightness and darkness is read and transmitted. The video image is actually made up of a series of horizontal lines but the scanning process is so fast that our eyes see the frame as a whole unified picture THE RASTER- horizontal lines starting at the top, from left to right. 2 TYPES OF SCANNING: a) progressive scanning- in order form top to bottom b) interlaced scanning- scans every other line, starting with odd lines (1,3,5…) then with even lines (2,4,6…) “FRAME”- two fields shown in rapid succession Each frame of video has 625 horizontal scan lines (PAL). But unlike the way we read it from left to right in successive order, the video image is scanned in a different manner. ODD numbered lines from 1-625 are scanned first, yielding half of the picture called odd field. The second scan from 2-624 yield the other half of the picture called the even field. The two fields make one frame (one complete picture). There are 25 frames per second with 50 fields per second. The camera processes 15,625 lines of picture information per second. RECORD AND REPLAY During recording, the tape passes over the 2-video heads rearranging the iron oxide impregnated in the video tape. The rearranged patterns created by the heads are the recorded signal. When the tape is replayed, the procedure is reversed and the configuration in the iron oxide particles of the tape is “read” by the same video heads and converts them to an electrical signal, and output this to a television picture tube which converts it to a viewable picture. CAMERA IMAGE SENSOR The image sensor of the camera is responsible for transforming light into electrical signals. When building a camera, there are two possible technologies for the camera's image sensor: - CCD (Charged Coupled Device) -light sensitive computer chip divided into pixels (picture elements) very fine grid spot- tiny light meters that reads the brightness of light at that spot 3
  4. 4. WORLD COLOR TV STANDARDS 1. NTSC (NATIONAL TELEVISION SYSTEM COMMITTEE)- 525/60 interlaced lines; 30fps, used in Canada, Japan, US, Philippines 2. PAL (PHASE ALTERNATING LINE)- 625/50 LINES, 25 FPS; used in UK, Western Europe, parts of Africa, Middle East, Australia and China 3. SECAM (Séquentiel couleur àvec mémoire, French for "Sequential Color with Memory" / Systeme Electronique pour colour avec memoire) -625/50 LINES; 25 FPS; - used in France, Eastern Europe, parts of Africa and russia * PAL AND SECAM – capable of sharper image than NTSC FILM/VIDEO OUTPUT PRIMARY FORMS OF STORYTELLING THROUGH FILM AND VIDEO: 1. NARRATIVE 2. EXPERIMENTAL 3. ANIMATION 4. DOCUMENTARY BRANCHED-OUT FORMS: 1. MUSIC VIDEO 2. PUBLIC SERVICE ANNOUNCEMENT / INFOMERCIAL 3. TV COMMERCIALS (TVC) 4. CORPORATE VIDEO / AUDIO-VISUAL PRESENTATION (AVP) STAGES OF PRODUCTION 1. PRE-PRODUCTION – planning stage 2. PRODUCTION – execution 3. POST PRODUCTION – finalization 4. *** ADPROM (ADVERTISING AND PROMOTION) – marketing and distribution THE WHO’S IN THE PRODUCTION 1. PRODUCER 2. DIRECTOR 3. PRODUCTION DESIGNER 4. DIRECTOR OF PHOTOGRAPHY / CINEMATOGRAPHER 5. ASSISTANT DIRECTOR 6. PRODUCTION MANAGER 7. SOUND RECORDIST / ENGINEER 8. EDITOR 9. MUSICAL SCORER 10. ADPROM 4