MULTIMEDIA - WHAT IS IT? DEFINITION 1: Uses a VARIETY of media ELEMENTS for instruction –Media elements are: text, sound, graphics, moving images (real.

MULTIMEDIA - WHAT IS IT?

• DEFINITION 1: Uses a VARIETY of media ELEMENTS for instruction – Media elements are: text, sound, graphics, moving

images (real or artificial)

• DEFINITION 2: Uses a VARIETY of media TECHNOLOGIES for instruction – Technologies are: correspondence study, satellite

video, e-mail, etc.

• A multimedia computer can run a slide show and/or display animated graphics with a full sound track of music, speech and sound effects.

• A multimedia presentation might contain:• Text• Animation• Digital Sound Effects• Voices• Video Clips• Photographic Stills• Music

Overview of GraphicsProperties of color

Essentially, color is light.

Colors has three fundamental characteristics:

hue, brightness, and saturation.

Related to the three characteristics of light waves:wavelength (hue), amplitude (brightness), and purity (saturation).

Hue varies as you move around the cone in a clockwise or counter-clockwise motion on a plane perpendicular to the vector of the cone.

Brightness varies as you move up or down the cone. The brightest color is at the top and the least bright color is at the bottom.

Saturation changes as you move in toward the center of the cone or outward toward the surface. The least saturated colors are in the center while the most saturated colors are at the outside surface.

Color space model

Properties of Pixels

A pixel is the smallest unit of programmable color on a computer display or in a computer image.

Every computer graphic is made up of a grid of pixels. When these pixels are painted onto the screen, they form an image.

Bitmap

A bitmap is a collection of pixels that describes an image.

enlarged

Bit depth is the number of bits used to store information about each pixel. The higher the depth, the more colors are stored in an image.

1-bit image (21 = 2 colors, black or white)

24-bit image (224 = 16777216 colors)

8-bit image (28 = 256 colors)

Resolution

Refers to the number of pixels per unit length on a monitor. It is usually measured in pixels per inch or dots per inch (dpi).

Monitors come in a variety of resolutions. They can get as small as 320 200 pixels or as large as 1280 1024 pixels.

Vector graphics

Vector graphics is defined by a sequence of commands or mathematical statements that place lines and shapes in a given two-dimensional or three-dimensional space.

For example, instead of containing each bit of a line drawing, a vector graphic file describes a series of points to be connected.

A straight line may be defined as:

In bitmap graphics

000000000000000000

000111111111111000

000000000000000000

In vector graphics

line ([4,2],[15,2]), where [4,2] and [15,2] are coordinates of two points, and line() is a command drawing a line between two points

Different features between bitmap and vector graphics

File size

vector graphics smaller

bitmap graphics larger

Change of an image size (rescale)

vector graphics: without loss of resolution

bitmap graphics: with loss of resolution

Vector graphics

Bitmap graphics

File size

12 Kbytes

File size

228 Kbytes

Some common file formats of bitmap graphics

GIF: commonly used for Web graphics. It only supports 256 colors. With compression.

JPEG: commonly used for Web graphics. It supports millions colors. With compression.

BMP: Microsoft's native graphic file format.

PICT: Apple Macintosh's native graphic file format.

TIFF: primarily used for scanned images (mostly scanned photographs) and is suitable for desktop publishing applications.

Some common file formats of vector graphics

EPS (Encapsulated PostScript): for the PostScript language. It uses a combination of PostScript commands and TIFF or PICT formats.

DXF (Data Exchange File): created by AutoDesk. Almost all PC-based Computer-Aided Design (CAD) systems support DXF.

WMF (Windows Metafile Format): for exchanging graphics between Microsoft Windows applications.

Digital Audio Capture

Analog (continuous) signal

digital (discrete) signal

When the amplitude of the analog signal is sampled at the instant, it is converted into a digital signal consisting of a number of digits. It is an approximation.

Factors affecting the conversion process

1) Number of bits used to represent different amplitudes of a sound signal

The greater the number of bits, the better the approximation.

4 bits 24 = 16 levels

8 bits 28 = 256 levels

16 bits 216 = 65536 levels (for CD player)

Factors affecting the conversion process

2) The sampling frequency (number of samples taken in one second)

The higher the sampling frequency, the better the approximation.

Nyquist's sampling theorem

If sampling frequency > 2 highest frequency,

the signal can be reconstructed with no distortion.

Telephone quality speech

Range: 300 to 3400 Hz

sampling frequency = 8000 Hz > 2 3400 Hz

CD quality sound

Up to 20 kHz

sampling frequency = 44.1 kHz > 2 20 kHz

Factors affecting the conversion process

3) Number of channels

One channel: mono

Two channels: stereo

file size of stereo sound file = 2 file size of the mono sound file.

Bit rate

= (number of bits / second) at the output

= number of bits used in sampling

sampling frequency number of channel

Example of bit rate calculation

For CD,

number of bits: 16

channel: 2 (stereo)

sampling frequency: 44.1 kHz

Bit rate

= 16 2 44.1k = 1411 Kbits / second

= 176 Kbytes / second

A song of 4 minutes long = 176 Kbytes 4 60

= 41 Mbytes

Example of bit rate calculation

For telephone quality speech,

number of bits: 8

channel: 1 (mono)

sampling frequency: 8 kHz

Bit rate

= 8 1 8k = 64 Kbits / second

= 8 Kbytes / second

Some common audio file formats

1) MIDI (Musical Instrument Digital Interface)

It is designed for recording and playing back music on digital synthesizers.

It records information about how music is produced: note-ons, note-offs, key velocity, pitch bend and other methods of controlling a synthesizer.

Advantage: very small file size.

Disadvantage: lack of specific sound control.

Some common audio file formats

2) MP3 (MPEG-1 Audio Layer-3)

It is a standard technology and format for compressing a sound sequence into a very small file (about 1:12) while preserving the original level of sound quality.

A compression algorithm reduces data about sound that most listeners cannot perceive.

Some common audio file formats

3) Wave file

It is an audio file format created by Microsoft. It has become a standard PC audio file format for everything from system and game sounds to CD-quality audio.

4) RealAudio and Shockwave

They are designed to allow real-time playback of audio directly from a Web site.

Digital Video Capture

What is digital video?

Essentially, it is a sequence of images output at a certain rate (e.g. 30 images/second) to make the eye believe that the objects in the images are in continuous motion.

What is Video Capture?

Using computer hardware, we are able to capture images from a video source (usually a video tape). Once captured, the video (or images) can be edited and manipulated.

Storage consideration

Consider a single frame (image) being displayed on a TV monitor.

Assume the frame size is 640 480 pixels

and one pixel requires 2 bytes (216 = 65536 colors).

Storage space = 640 480 2 = 600 KB

The frame rate of a regular TV is 30 fps (i.e. frames per second).

The total amount of required space for one second

= 600 KB 30 = 17.6 MB

Storage size of a CD-ROM is about 650 Mbytes.

It can store video of 650/17.6 = 37 seconds long !!

Thus it is necessary to decrease:

•frame rate (i.e. number of images per second)

•frame size (i.e. size of an image)

•image quality (i.e. number of colors used)

Usually captured video clips are smaller, play at a slower rate, or have colours less rich than the original.

Another approach to reducing storage requirement is compression.

Lossless compression: retain original data, with low compression rate (1:3)

Lossy compresssion: remove data that is unlikely to be noticed by the viewer, with high compression rate (1:30).

Some common video file formats

1) MPEG

It is the most popular standard. MPEG stands for Moving Picture Experts Group. It develops data model for compression of moving pictures and audio signals.

Compression ratio = 200:1

Different MPEG standards

MPEG-1: released in 1993

MPEG-2: released in 1995

MPEG-3: most popular version now

Different MPEG standards

MPEG-4: latest format, for video transmission over the Internet and mobile phones

MPEG-7: latest development project, an international standard by 2001

Note that .mp3 file suffixes indicate MP3 (MPEG-1 audio layer-3) files, not MPEG-3 standard files.

Some common video file formats

2) RealVideo

It is a kind of streaming video. When the user accesses a web site, the video clip continuously downloads while being viewed. RealPlayer (a free plug-in program for the web browser) is required to play the RealVideo file.

3) Quicktime

It is the proprietary standard of Apple Macintosh. The latest version includes the streaming feature (like RealVideo). Quicktime file can be run on both Macintosh and x86 computers.

Some common video file formats

4) AVI

It stands for Audio Video Interlaced, developed by Microsoft. It was the first video editing system. But it now has some problems (e.g. file size restriction and lack of driver support in interface cards).