HOW TELEVISION

WORKS

What Exactly is Television?

A process of transmitting images through a signal from one place or another

How Motion Pictures Work Motion Pictures/Movies the

process of projecting moving images to a wall or screen

Like TV, based on principles of persistence of vision and phi phenomenon

The illusion of motion is created by a series of frames presented sequentially

Film originally 16 fps (frames per second), but

standardized as 24 fps

How Television Differs from Motion Pictures Not one standard

international frame rate Frame rates range from

25-30 fps U.S. – National

Television Standards Committee (NTSC): 30 fps

Europe – PAL/SECAM: 25 fps

Digital Switchover: ATSC/DVB

Frames are not complete, but are composed of dots that are displayed/scanned horizontally.

Interleaved lines: fields—together make up a frame

What the Picture Tube Does A projected (scanned)

beam is made up of electrons that produced light when they strike the phosphorous coating on the inside of the glass inside the tube

Electrons respond to a magnetic charge, so electromagnets are used to control the aim of the beam in a very precise manner.

Gausing

TV picture tube images are made up of dots

Raster – the entire 280 X 525 field of dots

4 x 3: aspect ratio

What is RGB Chroma? Three scanning

beams activate three basic colors of a prism: RGB (Red, Green, Blue) Chroma.

Together the colors of light create a white beam

The Role of Color Bars Color Bars: The basic calibration and reference signal

used in color television developed by NTSC . They permit adjustment of color intensity, tine, and

black level (brightness and contrast) on a monitor.

How a Television Camera Works

Early cameras were quite large because the imaging device was similar to a picture tube

Eventually, this expensive, hot, and heavy tube was replaced by a charge coupled device (CCD)

How a Television Picture Gets to You (Transmission) In land-based trans-

mission methods, radio waves make it possible to the signal from the studio to your home.

Rise of use led to the digital conversion we discussed during the webquest.

In terms of satellite, there are 2 major systems: Traditional Microwave-

based frequencies DSS higher frequency

HDTV more resolution

Digital Television The digital channel

carries a 19.39-megabit-per-second stream of digital data

Transmission (cont’d): Digital, cont’d The reason that broadcasters

can create sub-channels is because digital TV standards allow several different formats. Broadcasters can choose between three formats:

480i - The picture is 704x480 pixels, sent at 60 interlaced frames per second (30 complete frames per second).

480p - The picture is 704x480 pixels, sent at 60 complete frames per second.

720p - The picture is 1280x720 pixels, sent at 60 complete frames per second.

1080i - The picture is 1920x1080 pixels, sent at 60 interlaced frames per second (30 complete frames per second).

1080p - The picture is 1920x1080 pixels, sent at 60 complete frames per second.

(The "p" and "i" designations stand for "progressive" and "interlaced." In a progressive format, the full picture updates every 60th of a second. In an interlaced format, half of the picture updates every 60th of a second.)

The 480p and 480i formats are called the SD (standard definition), while the 720p, 1080i and 1080p formats are HD (high definition) formats.

Digital Television (cont’d) The idea of sending multiple

programs within the 19.39-Mbps stream is unique to digital TV and is made possible by the digital compression system being used.

To compress the image for transmission, broadcasters use MPEG-2 compression

MPEG-2 allows you to pick both the screen size and bit rate when encoding the show.

A broadcaster can choose a variety of bit rates within any of the three resolutions.

Computer Video vs. Television Video Computer screens

have many times more dots

They do not interlace 2 fields (not needed with flicker)

Computer screen frame-rate can vary from 60fps to 120 fps

Complete the ChartTelevision Motion Pictures Computers

Purpose (original)

# Frames

Composition

Aspect Ratio

HOW VIDEO-

RECORDING WORKS

How Videotape Works

Videotape was a plastic-covered magnetic tape that is coated with a layer of microscopic metal particles. These particles were capable of holding a magnetic charge.

The VHS format came into prominence.

Videotape (cont’d) In the early 1990s, a

camcorder was invented that combined the aspects and features of a VCR and a camera.

The recording surface of a VCR is called a head.

Two types of recording processes: Composite Component

Generations: copies of an original

Footage: first generation tape

Analog Technology

Digital

Move over analog…. Digital Media CD-ROMS CD-RW DVD BLU-RAY

However, that is not necessarily the direction TV/video production is heading now

So how do we record now? Now, we record directly into the camera’s internal memory OR use

memory cards SD Card Secure Digital Memory Card SDHC Card High Capacity

Class 2: minimum sustained DTS of 2MB/sec Class 4: minimum sustained DTS of 4MB/sec Class 6: minimum sustained DTS of 6MB/sec Class 10: minimum sustained DTS of 10MB/sec

SD/SDHC Cards are examples of flash memory: http://computer.howstuffworks.com/flash-memory.htm

Then we save it onto a Hard Drive

Compression

https://www.youtube.com/watch?v=By30SCp-Tsw

Review

Answer Questions #1-14

Quiz Time!:○ History of Television○ How the Technology Works

○ Webquest○ This packet

Next week: Cameras & Composition