Graphics and multimedia: Videodisc

By -

Videodisc

IV can be based upon videotape or videodisc. The former is relatively low-cost, and can incorporate video material pro­duced fairly cheaply by the training institution itself. How­ ever, it has a number of disadvantages compared to the more sophisticated videodisc system described later:

• It takes a long time to wind through the tape to the start of a video sequence, unless that sequence is very close to the previous one.

• It cannot pinpoint sequences in the precise way that is possible with videodisc.

• It cannot pause on a video frame without distorting the image on the screen and, ultimately, wearing out the tape at that point.

• Programming the computer-based material for video­ tape is time-consuming, owing to the slow search time and the lack of an accurate frame numbering system.

For these reasons, videodisc material is much more suitable for IV.

The two main videodisc systems are Laservision (devel­oped by Philips) and JVC's VHD system (which is based on electrical capacitance rather than on the optical technology described below). Both types of disc are 30 em across, the same size as long-play music records.

Laser vision discs store information in the form of tiny pits burned by laser light in the disc's surface. Unlike compact discs, laser vision discs work on analogue rather than digital principles: the pits are in fact 'slices' of the waves recorded on them, as shown in Figure 7.6. Both the width of the pits and angles of the edges vary, and on playback these vari­ations are measured by a narrow laser beam which is reflected from them onto the reading head of the laser vision

image

player. There is no physical contact between the surface of the disc and the reading head, so Laservision discs are not worn out by repeated playings.

Laservision discs for interactive video are called active play discs. Each circular track of an active play disc stores one complete video frame (picture). The player rotates the disc at a constant angular velocity of 25 revolutions per second to play back the video at the standard speed of 25 frames per second.

If you think about this, you will realize that, unlike an ordinary music record, the player must spin the disc faster when it is reading the outer tracks of the disc than when it is reading the inner tracks. This makes for a complex playback mechanism, but it provides the user with a very versatile system:

• If the reading head is held stationary over one rotating track, one frame is reproduced and held on the screen. The reproduction is perfect, unlike the awful picture you get when you try to hold a videotape on a single frame. This means that you can use a videodisc to store still pictures, such as sets of slides. An active-play disc can store 36 minutes of video per side, and since each second of video playback uses 25 frames, it is easy to work out the number of still pictures that can be stored on one side of a disc:

36 x 60 x 25 = 54,000 pictures.

• Each frame can be identified by a number, and the player can access any frame simply by moving the reading head to the corresponding track. Any frame from the 54,000 stored on a side of a disc can be accessed in under 2 seconds. It is this numbering system that is used by the associated computer software to control the video player.

To make a videodisc, the video sequences must first be shot using the professional C-format video system. When the final tape is edited and ready, a videodisc master is produced from it using a laser light process, and the individual discs are pressed from this.

The production of the video film is the most expensive part of the process, though other elements, such as writing the associated computer program, are not cheap. The total cost of producing an interactive videodisc, with the software, is likely to exceed £100,000. As a result, IV training pack­ ages are expensive, often several hundred pounds per copy

- which is why there are not too many of them around in colleges. Nevertheless, IV packages are widely used in a number of big companies, where the large numbers who use them make this powerful training medium a cost-effective tool.

Comments

Post a Comment

Popular posts from this blog

WORKED EXAMPLES ON PROCESS SPECIFICATION.

By -
Image
PROCESS SPECIFICATION WORKED EXAMPLES 6.1 A bank has the following policy on deposits: On deposits of Rs. 5000 and above and for three years or above the interest is 12%. On the same deposit for a period less than 3 years it is 10%. On deposits below Rs. 5000 the interest is 8% regardless of the period of deposit. Write the above process using (i) Structured English (ii) A decision table 6.2 An organization maintains an employee file in which each record has following data: { Employee No., employee name, employee gross pay}. It has been decided to increase the pay as per the following formula: For pay of Rs. 1000 or less increase 15%. For pay of more than Rs. 1000 but up to Rs. 2500 increase 10%. For pay over Rs. 2500 increase 5%. (i) Writ e a structured English processing rule corresponding to the above policies. (ii) Express the policies as a decision table. (i) While employee records left in file do Read Number, name , gross pay 6.3 An offshore gas company bills it
Read more

Why do we need information systems, management structure, requirements of information at different levels of management.

By -
Image
Why do we need information systems, management structure, requirements of information at different levels of management NEED FOR INFORMATION SYSTEMS Information systems are needed when timely processing for fast action is needed, same data has to be processed in different ways and when organizations require innovative processing. MANAGEMENT STRUCTURE Functional areas of management are as follows: •PRODUCTION • MARKETING • MATERIALS – purchase, stores • FINANCE –Accounts • HUMAN RESOURCE DEVELOPMENT(HRD) • RESEARCH AND DEVELOPMENT (R&D) INFORMATION FOR MANAGEMENT A Production Management The following type of information is needed in production management: Strategic Information: 1)Yearly and monthly production quotas and alternate schedules 2)Policies on machine replacement, augmentation and modernization. 3)Identifying best product mix. Tactical Information 1)Identifying and controlling areas of high cost. 2) Identifying critical bottlenecks in production. 3)
Read more

The User Interface:Establishing User Interfaces

By -
Image
The User Interface Establishing User Interfaces The success factors in analysis start with the established interfaces from day one. What does this mean? You must start the process by meeting with the right people in the organization. In the best projects, the process is as follows: 1. Executive interface: There needs to be an executive-level supporter of the project. Without such a supporter, you risk not being able to keep the project on schedule. Most important, you need a supporter for the political issues that you may need to handle during the project (discussed in detail later). The executive supporter, sometimes known as a sponsor (JAD reference), should provide a preliminary schedule advising the organization of what is expected and the objectives of the project. The executive supporter should attach a letter to the preliminary schedule and send it to the project team members. The letter must put the importance of the project into perspective. Therefore, it is strongly rec
Read more