Powerplay

Multimedia Systems

Types of Media

* Text, hypertext and numbers:

o Text is any sequence of symbols that have a meaning.

o Hypertext is text presented in such a way that when selected new information will be shown.

* Audio is sound that has been digitised.

* Images are graphics or pictures, such as drawings, paintings or photographs.

* Animation is the movement of a graphic, a series of still frames being played in rapid succession.

* Video combines pictures and sound, played over time.

Print and Multimedia

* Mode of display:

o Printed information is displayed using a printer or plotter.

o Multimedia use screen and speakers.

* Interactivity:

o Print has limited amount of interactivity, at most it is possible to choose the sequence and content of the information presented by referring to the contents and/or index.

o Multimedia uses a great deal of interactivity, where it allows the user to choose the sequence and content of information. Hypertext and hypermedia are used to navigate through multimedia system.

Hardware Requirements of Multimedia

* Images:

o Pixel is a single picture element, smallest controllable element on a graphics screen.

o Most graphics systems have pixels controlled by data stored in systems video RAM or frame buffer.

o Resolution is measure of quality or detail present in a displayed image. Constrained by size of frame buffer.

o Bit depth describes number of data bits needed to store each pixel in an image. Sets no. of possible colours for each pixel.

o The number of colours is determined by 2 to the power of the bit depth. E.g. a bit depth of 2, would mean the number of colour is 2"2" therefore 4 colours.

o Palette is number of available colours for a graphic display or image.

o RGB is colour display system, that mixes different intensities of the three VDU colours in 24-bit (true colour) systems. Alternatives are HSL (hue saturation lightness) and CYMK (cyan yellow magenta black).

o Grey scales are shade of grey between black and white in a graphic display system.

* Audio:

o Waveform contains digitised sound. Sequence of sound measurements. Amplitude is the wave height and represents volume; wavelength is spacing between waves and represents pitch or note. More reliable playback; does not require expensive equipment. Files are very large, more CPU processing required, not possible to edit all characteristics of digitised sound.

o Musical Instrument Digital Interface contains instructions for musical instruments. Small file sizes, less CPU processing required, all notes and instruments can be edited, playback speed can be altered without affecting sound quality. Quality depends on attached musical instruments, cannot reproduce speech, editing requires some musical knowledge.

o Sample Rate is number of times a sample is taken from sound wave. Amplitude is measured and converted to a number. Common sampling rates are 44.1 kHz and 22.05 kHz. Higher sampling rate=better sound.

o Sample Size is no. bits per sample. Most common sampling sizes are 8-bit sound and 16-bit sound.

o Audio file size calculated by multiplying sampling rate, sampling size and time in seconds; if file is stereo, then result is then multiplied by a further 2.

* Video

o Video capture card used to convert analogue signals to digital signals.

o Frame rate is speed of video or animation. Measured by frames per second (fps). Higher frame rate=smoother video or animation.

o To calculate video file size, multiply frame rate by time in seconds, then find the file size for each frame by multiplying the resolution and the bite depth. Finally multiply these two results.

o Main problems with video are that it requires vast amount of storage space; and it also place huge demand on the systems processing capabilities.

* Animation

o Cel-based animation creates separate picture for each frame with only small changed between the frames.

o Path-based animation describes the path or movement of every object, the system then creates animation frames with each object drawn in its correct position.

o Morphing is where one image is changed, pixel by pixel into a completely different image.

o Warping is where a single image is gradually distorted by changing its pixels.

People in Multimedia Systems

* Content providers are people who provide material for multimedia product. Graphics artist, animators, researchers, script writers, musicians, actors.

* System designers plan and organise hardware and software required for presentation. Graphics artists, HTML authors, programmers, video directors.

* Project Manager organises the scheduling of various components of the product. Project leaders, producers, accountants.

* Technical Staff edit the graphic and video material, text and all other material into appropriate formats for final document. Audio/video editors, graphics artis, HTML authors, programmers, technicians.

* People may be multi-skilled and work in different aspects of the multimedia product, such as system designers also being project managers.

Examples of Multimedia Systems

* The examples of multimedia systems are:

o Educational multimedia users require more information content and more navigation options. Text is most common information data type.

o Leisure and Entertainment multimedia is heavily directed towards non-text based information.

o Information