CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Multimedia System Characteristic Reference: F. Fluckiger: “Understanding networked multimedia, applications and technology”, Prentice Hall, 1995

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Multimedia System Characteristic Multimedia systems must be Computer controlled. All multimedia components are integrated. The interface to the final user may permit interactivity. The information must be represented digitally.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Computer controlled Computer is used for –Producing the content of the information – e.g. by using the authoring tools, image editor, sound and video editor –Storing the information – providing large and shared capacity for multimedia information. –Transmitting the information – through the network. –Presenting the information to the end user – make direct use of computer peripheral such as display device (monitor) or sound generator (speaker).

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Integrated All multimedia components (audio, video, text, graphics) used in the system must be somehow integrated. Example: – Every device, such as microphone and camera is connected to and controlled by a single computer. – A single type of digital storage is used for all media type. – Video sequences are shown on computer screen instead of TV monitor.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Interactivity Three levels of interactivity: – Level 1: Interactivity strictly on information delivery. Users select the time at which the presentation starts, the order, the speed and the form of the presentation itself. – Level 2: Users can modify or enrich the content of the information, and this modification is recorded. – Level 3: Actual processing of users input and the computer generate genuine result based on the users input.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Digitally represented Digitization : process involved in transforming an analog signal to digital signal.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Analog and Digital signals Analog signal: a physical value which varies continuously with time and/or space. –TV signal, sound Digital signal: a time-dependent or space- dependent sequence of values coded in binary format. (discreet value)

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Analog/Digital & Digital/Analog conversion A/D converter : Analog -> Digital D/A converter : Digital -> Analog

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Process of digitization 1. Sampling 2. Quantization 3. Code word

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Sampling Sampling consist of retaining only a discrete set of values from the continuous set of values of the analog signal. Analog values are generally captured only at regular time or space intervals.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Quantization A process of converting a sampled signal into a signal which can only consist of discreet values. E.g: only use positive and negative integers.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Code-word generation A process of associating a group of binary digits, called a code word to every quantized value. E.g: quantized value 18 is associated with binary code-word “ ”.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Why represent information in digital form? Storage Transmission Processing

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Why represent information in digital form? Storage –The same digital storage device can be used for all media –The only difference lies in size requirement for each media. –Images, sound and video require larger volumes than text.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Why represent information in digital form? Transmission –A single communication network supporting digital transmission can be used to transmit information in all media type. –Benefits: Digital signal is less sensitive to noise. Error detection and correction can be implemented Encryption of the information - easier

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Why represent information in digital form? Processing –Editing : cut and paste function, mixing information from different media is possible –Quality improvement : removal of noise or error (sound), image enhancement –Recognition of the meaning of the information – image processing

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Why represent information in digital form? Summary –Digital representation permits the storage of different information types on the same devices. –Information may also be transmitted over a single digital network. –When digitized, all form of information may be treated by computer programs, for editing, quality improvement, or recognition of the meaning of the information

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Drawback of digital representation Coding distortion –Loss of information during sampling, quantizing and coding sampled value –Signal generated after D/A conversion is not identical to the original one. –Solution: increase the sampling rate and increase the number of bits to code value –Problem: increased bit rate -> larger storage and bandwidth.

CMPD273 Multimedia System Prepared by Nazrita Ibrahim © UNITEN2002 Drawback of digital representation Storage –Large capacity to hold multimedia data