Low
cost hardware and software is now available
to transform your Personal Computer
into a MultiMedia workshop.
TEMPRA
PRO is
a fully functional 24 bit colour image
editor which can be used to create, import and
edit colour pictures. Images can be scanned
from a variety of scanners or captured
directly from a video camera.
TEMPRA
SHOW is
a MultiMedia development system
and a menu-driven storyboard editor for presentations.
This exiciting new medium has been
built to give you the power to express your thoughts
in a simple and flexible manner.
CREATIVE LABS MULTI-MEDIA
UPGRADE
KIT
includes
the Sound Blaster Pro stereo card,
MIDI Kit, a high-perfromance CD-ROM drive, Microsoft
Windows* version 3.0 graphical enviroment
with Multimedia extensions 1.0, Sound Blaster Pro software and
additional CD-ROM titles.
MICROKEY/DIGIVIEW
is an AT compatible expansion
board that captures near photo quality images
from still or motion video sources and
displays full-colour motion video in a window
on standard VGA monitors.
For more information contact
us on
TEL
(0923)
240272 FAX
(0923) 228796
26Greenhill.Crescent. Watfordbusinesspark. Watford. Hertfordshi re. Wdi 8xg
Task 9
Writing
Work in pairs. You manage a company specializing in multimedia hardware and software. Prepare a leaflet to inform companies of the potential benefits of using multimedia. Invite them to contact you for a free consultation.
Computer-to-video
conversion
Reading
Task 10
Read the text opposite and answer these questions.
What are the main differences in the way images are produced on a TV screen and on a computer screen.
Why did the developers of the PAL system invent interlaced video? What are its advantages and disadvantages?
Which of the two suggested ways of getting a signal from a computer to record on a VCR do you think is preferable? Why?
160
-iS-
How
they work
Although the computer screen has the standard characteristics of a TV display, images are produced in a very 45
5 different way. If you want to record anything from your computer to video for play-back on a TV monitor, you need a print-to-tape device. In a TV display, a tight beam of 50
10 electrons scans the screen in much the same way you read a page of text-from the upper-left corner, it moves line by line to the lower right. Usually, one pass writes the 55
15 entire image once. The number of passes the beam writes per second is called the vertical refresh rate and is measured in kiloHertz. Most computer systems follow the 60
20 American TV standard and use a vertical refresh rate of 60kHz whereas PAL, the European TV standard, requires 50kHz. Another difference is with 65
25 bandwidth. When PAL was defined, the bandwidth available for a TV signal was very narrow. While the TV image had to be refreshed at least 50 times a second for flicker to 70
30 remain unnoticeable, there was not enough bandwidth to transmit all 625 lines of one TV image in a fiftieth of a second. The developers of PAL, therefore, employed a 75
35 clever trick called interlaced video. They split each frame of the image into two fields of 312.5 lines, the odd lines into field A, the even ones into field B. The fields are 80
40 transmitted at a rate of 50 per
second, leaving us with an effective
frame rate of 25 per second while eliminating most of the flicker.
This is fine for viewing from several yards, but should you move as close to your TV as you would to your computer screen, you'd end up with a headache after half an hour. Also, if any parts of the displayed image occupy only one horizontal scan line, that scan line will flicker quite noticeably at 25kHz.
All video equipment works with PAL-standard, 50kHz interlaced video. Computers tend to use 60kHz (or more), no interlaced video and look more stable. To get a signal from your computer to record on a VCR, there are two possibilities:
Use a display adaptor that can produce PAL-standard video. You would not be able to connect such a card to a standard computer monitor, however. A video monitor or a multi-sync monitor is needed. You wouldn't want to look at such a screen for hours on end - interlaced video is not suitable for word processing.
Put up with the standard display signal from your computer (probably 60kHz) and use a scan converter. It can take a video signal with one refresh or scan rate, and convert it to the other. A scan converter is actually a small digital frame-grabber with asynchronous video output.
Task 11