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Television Com 240, Dr. McMullen Class Notes and Study Guide |
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Part 1 The Technology of Television: (So I Can Understand it....) |
Reading assignment: Burrows Ch 5, 6, 7,8,9,11,13 & 14 (For entire television unit)
When we learned about audio, we learned how the signal flowed from the mic, through the mixing bus, patch panel, etc. Think of video the same way.
What are the 3 functions of the audio console?
All of those things occur with video as well.
The camera, like the mic is a transducer (what is a transducer?)
Signal is channeled through video switcher
Some mixing occurs in video switcher
Some shaping occurs in switcher
Most shaping occurs in CCU (Camera Control Unit)
Amplification may occur at several places along the route
Monitoring also occurs at several places (discuss)
Because it take s 600 times as much information to produce a video signal as an audio signal, lots of things can go wrong. Any synchronizing errors can cause the picture to tear, break up or distort.
Our brain is illustrative of the complexity of visual signals. Optic nerves have one million nerve fibers, while auditory nerves have only 30,000. We use 30% of our brains for visual purposes but only 3 percent for auditory senses and 8 percent for touch. In effect we collect a full megabite of visual information in a fraction of a second. (Sources:Lindstrom, Robert. "The Emerging Visual Experience." Knowlege Industry Publications. White Plains NY : 1999)
Several pieces of equipment are used to adjust and stabilize the picture.
SYNCHRONIZING GENERATOR: "Synch Generator" acts like electronic "sprocket holes." (Ask : What are sprocket holes?) Keep everything coordinated and "together."
PROCESS AMPLIFIER: stabilizes levels of brightness, color and synchronizing information and removes unwanted noise.
TBC or TIME BASE CORRECTOR: When video tape is played back, some the synchronizing information may be slightly damaged or altered (that would result in distortion, break-up, etc.). The TBC encodes these signals digitally and makes an enhanced synchronizing signal for playback and editing.
FRAME SYNCHRONIZER: Matches synch information from outside sources" to studio specs. An outside source might be a network or satellite feed.
COLOR BAR GENERATOR: Sets a standardized pattern which can be matched just like the audio "tone" at the beginning of a tape. (Explain again how the "tone" works)
OSCILLOSCOPES: Remember this is like a VIDEO VU METER. They come in two types:
Just like in audio, don't trust your monitors regarding color and brightness; they can be maladjusted.
NOTE: pay special attention to Fig 5.1 pg. ___ Burrows
The camera pick-up tube is a cathode ray tube that transduces visual pictures into electrical signals. A solid state sensor, called a CCD, may be used in stead of a tube.
Either way, the camera lens focuses an image of the scene onto a light-sensitive surface. On that surface, the light image creates a pattern of tiny electrical charges which correspond to the light and dark in the shot.
Since the charges depend on the amount of light falling on each point, a fluctuating voltage results which provides an electrical replica of the light, shade and detail of the scene.
That fluctuating voltage is the VIDEO SIGNAL.
In order to understand how the camera works, you must understand some basic principles of light. (remember how black it was when I turned out the lights in the studio?)
White light is actually made up of a spectrum of colors: red to violet.
Some terms you need to know before we go on:
HUE: The actual color without reference to brightness or saturation.
SATURATION: The purity of the color.
BRIGHTNESS: The strength or intensity of the color.
COLOR TEMPERATURE: The dominant color of a light source in degrees KELVIN.
About COLOR TEMPERATURE:
(Remember your high school chemistry classes and that old Bunsen burner? The hotter the flame, the bluer it was. Cooler flames were red or yellow.)
For examples of color temp. see p. 94-95 in Whittaker.
Two color temps are standard:
But when cameras are adjusted for temps, remember that shade is going to be different than full sun; morning temps will be different than noon-day, etc. So you must re-white balance cameras when you change lights. Otherwise when you try to edit your different shots together.
The camera has to be readjusted, but our eyes don't. That's because they automatically readjust in a process called approximate color consistency. We see a white object as white in dim or bright light, and we adjust out perception of related colors accordingly.
Another characteristics of our eyes is a process called simultaneous contrast. When we look at a strong color, our eyes automatically shift to supplement the surrounding objects with color from the opposite side of the spectrum or color wheel -- the complimentary color. So when you design a graphic or a logo, you want to choose complimentary colors because each makes the other look stronger, brighter, more memorable.
Simultaneous contrast can also cause problems. A person with RED hair, probably wouldn't want to wear orange or yellow.....Those colors wash out, or detract from skin tones....So you see sets with cooler colors in the background, and you don't see a lot of red dresses on TV either. (There are other reasons for that too) Draw a color wheel for illustration:
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12:00....... Red 2:00......... Magneta 4:00......... Blue 6:00 ........ Blue-Green 8:00 ........ Green 10:00 ...... Yellow |
The colors opposite each other are COMPLIMENTARY COLORS.
Simultaneous contrast also impacts grays. A white object will look whiter against a black background and greyer against a gray background.
REFLECTED color is also important. Remember that red-haired lady in the red dress? The red from her dress may reflect only to her face and make her skin tone look redder. This might be good for a person without much color in the face. Photographers recommend that people wear warm colors for pictures for that reason. That is also the principle behind "having your colors done..." (If you are going into Broadcast Journalism, I highly recommend you have that done.)
More must be understood in order to really appreciate how this works:
ADDITIVE COLOR VS. SUBTRACTIVE COLOR
Light is based on additive color; pigment is based on subtractive color.
Subtractive color: Applies to anything that has color in it....clothes, painting, etc. The REFLECTED light we see. (explain the process)
The color we see in a shirt is blue because all of the colors in the light in the room except blue are absorbed (or subtracted) and the blue light is reflected back for our eye to see.
Note: What happens to the light which is absorbed? It is transformed into HEAT! That's why black cars are so much hotter in the summer here and dark colored clothing is warmer than lighter colors.
THE PRIMARY COLORS in SUBTRACTIVE COLOR ARE: red, yellow and blue (actually magenta, cyan, yellow are more accurate)
When all the primary colors in subtractive color are added together in equal parts you get BLACK!
Filters can be used in cameras to SUBTRACT COMPLIMENTARY COLORS. Use a cyan (blue-green) filter will block red and reduce the degree of yellow and magenta. It will allow blue-green and most other greens and blues to pass through.
ADDITIVE COLOR: Applies when COLORED LIGHTS are mixed (Not paints or pigments)
ADDITIVE PRIMARY COLORS are red, blue and green.
Actually the eye doesn't respond equally to all colors. Human eyes are more sensitive to yellow-green whites than bluish or reddish lights. So in order for the camera to record something which can be reconstructed as white to the viewer, the colors are weighted:
(Whittaker p. 100)
Now let's go back to those characteristics of color we mentioned earlier:
When we talk about primaries being mixed to make other colors, we have to discuss saturation.
Which is more saturated? A royal blue shirt or a turquoise one? WHY?
In TV, saturation is inversely related to grayness/whiteness. (WHY?)
Discuss GRAY SCALE (Cosby sweater example)
STRUCTURE OF THE CAMERA TUBE:
Two types of signals:
luminance = brightness
chrominance = color information
SCANNING PROCESS:
Most colors are not "true" but mix of other colors
Some camera have only two CCD's. Because we know the proportion of the two CCDs, we can figure the proportion of the third one: A + B + C = 100
IF you white balance, focusing on a white card and that = 100, camera can determine the other proportion. Thus, NTSC cameras can function with two CCDs..
Camcorders have only one CCD. Filters with microscopic color stripes are places over the CCD. These filters with some computer assistance can break apart the picture into the primary colors. Using this system, some color cameras as small as a peanut have been made. (Whittaker, p. 101.)See p. 122 in Burrows for diagram.
You already know about color temperature. White balancing is important because of that. It is also important with these one and two chip cameras.
How do you white balance?
Some consumer camcorders have automatic white balancing.
Remember to white balance when you go from one light level to another.
It is possible to "fool" the camera
Once the signal leaves the camera all of the information gathered in the tube remains as a "pure" line video format and processed in that form (as mentioned above)
See p. 125 in Burrows
The receiver or KINESCOPE tube
NEVER is a total picture/frame on the screen at one time, but we don't see the lag.
TYPES OF RECEIVERS:
Standard NTSC:........... 525 lines ...................... 400x500 pixels
Standard VGA monitor:....................................... 640x480
Standard SVGA monitor:................................... 800x600
LCD Color Displays:
New generation of LCD screens: Flat panels which can provide computer displays where ever they are needed. Portable devices for use with presentations. Expected to go to the consumer market in 1998 or 1999. These flat panel displays will allow multimedia to be displayed in places where it could not have been before; art galleries, etc. Endless possibilities. (Multimedia Producer, 4/96 p. 80)
PLASMA DISPLAYS:
Based on PALC: Plasma Addressed Liquid Crystal
The plasma discharge phenomena, which results from passing voltage in a tube filled with low pressure gas, is frequently used as a light-emitting source. Here the plasma is used as an electronic switch and works something like a transistor.
Advantages over other display formats:
Large format CRT monitors:
LCD monitors
Advantages of Plasma Display:
How they work:
The display panel is a large matrix of tiny glass cells. Each one is filled with several gasses. The cells are placed in a sandwich between glass sheets which have tiny tubes in them. Those tubes attach to the glass cells and that's where the pixels are formed. The color is added by RGB stripping on the cells. Three sets of electrodes are placed on the rear glass and when that is charged, the gas in the cell glows creating the light.
These are easier to build than CRT monitors
(Source:"Gas Plasma Monitors: Windows of Opportunity ." Supplement to AV Video and Multimedia Producer. 4/99 )
Lindstrom, Robert. "The Emerging Visual Experience." Knowlege Industry Publications. White Plains NY : 1999)
Difference between computer monitor and TV screen:
VISION TOUCH from Sony will combined a wireless controlled and PC controlled audio/video interface that can automate "an entire home full of electronic devices"
NOTE: Not all colors can be reproduced accurately.
[watch ST: uniforms....you can never be sure what colors the science uniforms really are]
Accurate vs. "good" color: Studies have shown that Americans like their colors BRIGHT--even brighter than they appear in nature. This is especially true of skin tones and sky blues.
TUBE REGISTRATION: the color tubes in the camera need to be "REGISTERED" to make sure they match properly, to produce the correct colors.
Because of PERSISTENCE of VISION -- makes the brain "see" the "flashes" as a continual moving picture.
Some notes about types of TV Systems:
NTSC: system
Problems with NTSC:
Pal:
625/50 Hz system
Much of Europe
SECAM:
625/50 hz. system
France, Eastern Europe and much of Asia
The other systems are necessary because not all countries use the same 50 hz electical system that we do. So they use 50 frame and 25 fields per second. They have a sharper image because of added 100 lines, but the slower frame rate means some flicker is noticeable.
Since the U.S. is the largest exporter of television programs...How are our programs converted to a foreign standard?
Brand new technology....
VIRTUAL RETINAL DISPLAY: Uses a modulated, low power beam of laser light to "paint" an image directly onto the retina of the viewer's eye (in a raster scan pattern similar to that of a TV set). It creates a high resolution, full-motion, multi-color image without the use of screens or externally projected images. It looks to the viewer as though the picture is right in front of him, but can be adjusted to "see through" so you can see what you're doing as well! The device is put into glasses or helmet. (See ADVANCED IMAGING, October, 1997 p. 14)
Many of these technical problems will be hopefully solved with advanced tv, commonly known as HDTV : High Defintion TV. Go to Television: Part 2 HDTV
Resources:
Copyright, 2001
Janet McMullen
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