Sydney University Lecture Series 2001 IPT Option Topic Multimedia By Peter Cox

Characteristics of Multimedia System Multimedia is the joining of more than one type of media. It includes text, still images, moving images, animations, sound.  Text: Letters, numbers and other characters  Hypertext: Non-linear text where the reader travels through hypertext by following links of interest.  Audio: Sound that has been digitized  Images /animation: - Bit-mapped graphics: Each pixel of image on the screen represents a bit of memory. - Vector: Made up of objects like straight lines, curve, or a shape - Animation: Movement of graphics.  Video: Combines pictures and sounds displayed over time.

The roles people play in a Multimedia Production ProducerGraphic designer: Project manager:2 D animator Writer3 D modeller Content expertProgrammer Information designerSound artist Interface designerVideo producer Art directorServer administrator

Image Characteristics  Pixel is the smallest controllable element on a graphic screen  More pixels in a display (high resolution) mean more information and details can be shown  The relationship between the image on the screen and the bits in memory (VRAM)is called bit mapping.  Bit depth (colour depth or pixel depth) for images is the number of bits per pixel.  Screen has over pixels in a screen 640 * 800 Each pixel is controlled by data stored in "Video RAM" or "Frame Buffer"

Image Characteristics Bit-Depth Combination Binary Number Shading / Colour In this case a pixel in a screen or image has a memory of 3 bits allocated to it which give it 8 combinations of shading or colours. 0000white black 3 bit

IMAGES Bit Depth (bits per pixel) Number of colours or tonesRelationship = = = = = = , =65, ,777, =16,777, ,294,967, =4,294,967,296

IMAGES The file size in kilobytes of a black and white image with a screen resolution of 640 * 400 pixels is: Horizontal pixels * Vertical pixels * Bit depth File Size = 8 * 1024 bits 640 * 400 * 1 File Size = 8 * 1024 = = Kb

Image Data Formats Lossy Compression: Removes a number of data bytes from the file that result in a smaller file but also reduced quality. Lossless Compression: Replaces repeated data with something that takes up less room, hence the original file can be recovered. BMP: Bitmap format is a simple uncompressed image format. JPEG: Joint Photographic Experts Group: this format uses a variety of mathematical transforms to achieve the best compression rates. However it is "lossy" compression, which sometimes creates distortion. GIF: Graphical Interchange Format is mostly used for on-line images. Owes its success to flexibility, high compression rates (using lossless compression) and lots of supporting freeware.

Displaying Images System Palette: maximum number of colours available in a display system or graphic Palettes on an 8 bit system or 8 bit monitors contain 256 colours or less. Colour-tables contain data information describing image colours stored in image file. To make images load fast on the Web - Include height and width attributes in your IMG and EMB - Use interlaced GIF's and Progressive JPEG's

Processing Images Problem: Converting an image from a 24-bit true colour to a limited number of colours available on on any palette, there obviously has to be a compromise. Dithering: Process by which a computer displays a broad range of colours with a more limited range of colours to create the perception of a new colour that is not actually present in the range. Example: On an 8-bit display, when a browser encounters a 24-bit image, it dithers the 24-bit image to an 8 image.

Collecting Image Data Images need to be digitised. This involves: converting an image into bit patterns within computer memory Devices to Digitise: - Scanners (hand-held scanners, flat-bed scanners) - Digital Camera - Digital video Factors that effect size of Image: - DPI (dots per inch) number of pixels that will be created for every inch of scanned image) - Area to be scanned - Bit depth

AUDIO Sound waves travel through the air as waveforms (analogue data), its characteristics are: Amplitude: wave height (volume of sound) and Wavelength: spacing between waves - pitch or note. Analogue data: are continuous changing quantities. Digital data: 1 or 0

Collecting Audio Data Sound is digitised by taking regular measurements from the sound wave. Factors that affect the quality and size of the digital waveforms are: - Sampling rate: number of times a sample (slice) is taken from the sound wave per second. (common sample rates are 44.1 kHz and kHz). - Sample size: (bit resolution) is the number of bits taken per sample. Common are 8 bit sound (used for most voices) and 16- bit sound (used for bit sound (used for better quality). - Channel: Stereo (2 channels) or mono(1 channel)

File Size = (sample rate * sample size * time) * channel Example: You want to record a speech that goes for 3 minutes and is to be played on a stereo system. File Size = (11,000 * 8 * 60 * 3) * 2 = bits = bytes = 3876 KB = MB Sampling rateused 11 kHzFor speech 22 kHzMusic playback 44 kHzCD quality

Common Audio Formats  WAV: Microsoft = IBM, Store 8bit or16bit. Requires large file size  MIDI:Musical Instrument Digital Interface. MIDI instrument. File format called MIDI sequence. Contains only note information –NOT details of sound. Requires less storage.  MP3:Compression ratio 11:1. 44MB – 4MB. Removes high and low frequencies that are out of human hearing.  Real Audio :Standard exchange format over the Web. Needs RealAudio Player Plug-in.

VIDEO Of all multimedia elements, video places the highest demand on your computer and its memory. Video whether in analogue or digital form, is an electronic representation of a sequence of images.

Video Processing Digital Video Requires:  Huge files for storage  Large bandwidth for transmission across networks  Fast processors to manipulate image and sound processing

Calculate the file size in kilobytes of a 15-minute movie at 24fps. Each frame is 600 * 800 with 24 bits per pixel. File size = number of frames per second * file size for each frame  Number of frames per second = frame rate * time in seconds  File size for each frame = horizontal * vertical * bit depth Number of frames= 24 * 60 * 15 = 21600frames File size for each frame=600*800*24 = bits File Size = * /1024 File Size = KB = MB

Video on the Web can be delivered by:  Download and Play   Streaming: Specially formatted time-based media-animation. Begin playback before file is completely downloaded. Problem: Internet data is Packet-based and wasn’t designed for continuous/synchronized delivery.  Fast-Start QuickTime

Collecting Video Data  Digital cameras  Video cameras

ANIMATION Animation is created from a sequence of still images. The images are displayed rapidly in succession so the eye is fooled into perceiving continuous motion. Whether animation is created for movies, videos, computer presentations, all the information that you see is located in frames. The term frames per second (fps) is used to tell how fast a movie is being played. General standard is 24 fps for motion pictures or film and 30 fps for videotape.

Animation Processing Requires a lot of processing: For example a video running at 30 fps for three minutes (30 * 60 * 3) = 5400 frames This could work out to a lot of memory depending on how many bits each frame is. Cel Based: Animation cels are layered to produce a single animation frame. For each frame there is a separate cel for the background and for each object that moves independently over the background. Path Based (tweening) Involves showing the movement of an object onto a fixed background along a particular sequence or path.  A sprite is any part of your animation that moves independently of the background, such as a bird flying across the screen.  You attach a sprite to a motion-path curve that is drawn through the positions of the sprite in successive frames. Morphing: smooth change between two different objects. Warping: Distorting a portion of an image.

Common Video and Animation file Formats  Animated GIF (.gif) : sequence of frames displayed on web.  MPEG (.mpg) : Format for compressed video. Uses lossy compression. Only stores changes from one video frame to the next. MPEG1-Standard resolution:353*240*30fps(VCR) MPEG2- Standard resolution:1280*720*60fps (TV,DVD)  QuickTime (.mov): Application for display and playback. Codec compression software installed. Web browser QuickTime plug-in needed.  Macromedia FLASH (.fla)  AVI (.avi) CODEC: Software that encode/decode various types of data. Typically used in sound and video files. Installed in Quicktime.

A storyboard defines the screens and the navigation paths between them. There are four storyboard layouts: Linear: simple sequential path Hierarchical layout: top-down design in which user starts at the beginning and moves down through the site Non-linear: no structure, the user moves between different layouts in any direction Combination layout: a combination layout: a blending of the above layouts ( Non Linear Topology or Combination Topology ) Flash Introduction Table of Contents Catalogue of Chairs Catalogue of Cabinets Catalogue of Tables Catalogue of Upholstered Products Catalogue of Interior Objects Catalogue of Chairs Catalogue of Cabinets Catalogue of Tables Catalogue of Upholstered Products Catalogue of Interior Objects About Company

COPYRIGHT To get a full understanding of Copyright Issues visit the Australian Copyright Council web site.

COPYRIGHT What is Copyright protected Who owns Copyright in a web site How can you get Copyright? How do you protect your Site? What does Copyright mean on the Web? Producing a web site Issues Social, Ethical and Business Problems

Questions Describe the information technologies needed to develop a multi-media web site for a Music Band. Compression & Animation Technologies. –Animation: FLASH –Sound compression: MP3 –Compression and viewing video: QUICKTIME How could you evaluate this product –Visitor counter –Guest book –Download time –All links work What does interactivity mean and how can this web site be “Interactive” –Roll over images and links –Hypermedia text –Image maps –Flash animation and links

Issues What are some technical and ethical issues you need to consider with this web site. –Technical: Download time (images,video,sound,animation) –ISP access –Ownership of “work”. Who owns it? –Ethical: Copyright access to your material

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