HSC Multimedia

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What is Multimedia?• the combination of a variety of different media (data types):

• text and numbers

• audio

• video

• images

• animation

to add interactivity, hypertext and other forms of hypermedia.

What is Interactivity?• refers to the user being able to make an immediate response to the product and modify processes

• there is a dialogue between the user and the input device

• this communication may result in linear or non-linear path through the product

• dynamic interactivity results when the product changes, depending on the action taken by either the author and/or the user

• some products use indexing to remember position in the product

Characteristics of Multimedia

• it can increase the impact of the message or impact on the user

• multimedia systems involve interactivity information on demand, as required, controlled by the user, can be self-paced, cross referenced via hyperlinks

content can be selected by user learning style (learn by doing)

involves multi-senses

Characteristics…..Characteristics…..

• can involve more than one input device

• can be structured to build on previous learning

• can have feedback on performance

• can be repeated (over and over)

• hyperlinks / hypertext can be utilised (navigation buttons)

• involves the user in the presentation

• allows input, provides output

• it is generally dynamic, not static

TextText

• Strings of printable characters separated by white space characters (letters, numbers, symbols)

• main method of conveying information through language

• text size / style can be used to emphasis content

• used for titles, headlines, menus, content

• software can ‘speak’ text

Hypertext /HypermediaHypertext /Hypermedia

• Text presented in such a way that supports direct, intuitive navigation between elements of the text of other information

• Hotspots can also be used :• usually termed hypermedia as they are often linked to images,video or audio media

• text / hotspots are linked with other cards / pages/ documents

Digitising dataDigitising data

• Presentation of the product• CD-ROM, DVD, Video

• Analog v Digital

• size and type of files

• quality of product

• timing sequence• planning - storyboards

Lossy vs LosslessLossy vs Lossless

• Lossy compression removes a number of data bytes from a file.The resulting file is smaller in size but the quality is reduced

• However, audio and video files can be compressed with high compression ratios and without any change noticable to the human ear or eye

• Lossless compression allows the original file to be recovered in full.It works by replacing repeated data with something that takes up less room

Images - Bitmapped vs ObjectsImages - Bitmapped vs Objects

• BITMAPPED• a section of memory consisting of a series of zeroes and ones corresponding to pixels on the screen

• for colour, a number of bits are used to represent the colour value of each pixel

• a correspondence between memory locations and elements of the output pattern on various output devices

• the frame buffer is a section of memory used to store that data forthe current image being displayed

• Bitmapped images usually require anti-aliasing to remove ‘jaggies’

• Jaggies - the staircase roughness of oblique lines and polygon edgesin computer images caused by the underlying squareness of the pixel

• Anti-aliasing - the process of removing faults such as jaggies in computer images caused by the physical size and shape of the pixel

• OBJECTS / VECTOR

• stored as mathematical entities, eg. Coordinates, width, colour, intensity etc

• the vectors are defined only by their starting and finishing points

• vector graphics are also known as objects

• typically these images are smaller in file size and easily scaled than bitmapped images

DitheringDithering

• Dithering - the representation of a colour not available in the existingpalette by the use of a pattern of varying colours where the eye performs the averaging to produce the required colour

• a Mask can be used to protect an image and not allow editing

• to alter the size of the file, combinations of colour palette and dithering can be used

Common Image File TypesCommon Image File Types

JPG (Joint Photographic Expert Groups). A lossy compression format designed to reduce the size of full colour bit images

GIF (Graphics Interchange Format). Bit mapped format that uses a lossless compression algorithm. Limit of 256 colours.

PICT Apple graphics format that is either bit mapped or vector graphics

TIFF (Tagged Image File Format). A bit mapped format, standard choice for scanned images

PNG A new file format that is becoming more popular. It supports 24 bit colour images, has an interlacing option and offers more powerful compression than JPG

EPS (Encapsulated Postscript). Uses vector graphics and often will only be interpreted by a printer. Therefore it cannot be displayed on the screen

BMP (Bit Map). An uncompressed bit mapped file format.

AudioAudio

• Sound is analog in nature, and to be used in multimedia, needs to bedigitised

• creates mood, interest, includes speech

• audio files are usually large files unless they have been compressed

• Audio can be in 2 basic formats:

• a digitised file of the actual sound eg. WAV file or in compressed format MP3

• MIDI (Musical Instrument Digital Interface) where details of the characteristics of each note is filed

Digitised AudioDigitised Audio

• the quality of the sound depends on the sampling rate, sampling size, time and number of channels

• sampling rates are from 10 to 44 kHz with CD-ROM having a sampling rate of 33kHz

• slow rates result in loss of quality and distortion

• sampling size refers to how many bits are used to record (bit resolution)

• 16 bits gives 65536 possible level of sound

• 8 bits gives 256 (and smaller files)

• sound can also be in mono (1 track) or stereo (2 track)

• CD-ROMs are popular storage devices as they allow direct (non-linear) access.

• 44kHz at 16 bit for 60 sec = 10.5Mb

• 22kHz at 8 bit for 60 sec = 2Mb

Audio CompressionAudio Compression

• Minimal Hearing Threshold• the human ear can only receive sound between 20Hz and 20kHz• any sound not within this range is discarded as the information is of no use

• Masking Effect• when you hear sounds, the louder, more prominent sounds mask the quieter sounds• in terms of compressing the sound, we can remove the quieter sounds that we cannot distinguish from the louder sounds

• Managing Sound Redundancy• where a sound occurs simultaneously on both channels, it is recorded once for both channels to use, rather than recorded separately

Digitised Audio File TypesDigitised Audio File Types

WAV Sampling in 8 and 16 bits, stereo and mono. Lossless compression

MP3

Breaks sound into short time segments, filters into frequency bands then using a mathematical model of human hearing, sends the most audible parts of the signal to the output stream. If the bit rate is high enough it is lossless compression but for the Web it is certainly lossy compression.

AIFF Sampling rates of up to 32-bits are supported. There is no data compression for AIFF files so files tend to be very large.

MIDIMIDI

• The details of the actual notes played, on, off, velocity, pitch bend, after touch,

program change, length, tone, etc. are all kept in the file

• MIDI files when played require a MIDI keyboard or device to interpret the notes and then produce the sound

• MIDI files are used by musicians to multi-track, mix and write scores

• Hardware required includes controller (keyboard), synthesiser, MIDI port and a computer running MIDI software

• hence file size is very small

VideoVideo• Video is real image recording• usually requires data compression (CODEC) to allow a smaller file, and decompression to play• requires high VRAM and storage space• typically, 20 minutes of video is 8GB. Since 1 frame at 24 bit = 1Mb• file types include MPEG (Lossy) and Quicktime, AVI (Lossless)

• Lossy CODEC’s find data that can be removed and delete this without much quality loss thus making the video smaller• Lossless CODEC’s look for patterns of pixels replacing them with a code between each frame

• for example: the background may be stationary and the person moves, so the background is saved using a code which represents it, and only changes when a new background appears

• Digital video cameras simplify the process, as “S” video or firewire ports allow transfer of digital data between the camera and computer• to reduce file size the frame rate, screen area, palette, file type and CODEC can be changed• Video cards usually allow frames to be captured (frame grab)• can be edited via software (including iMovie, Adobe Premiere, Quicktime, Quicktime VR)

Video File TypesVideo File Types

AVI

Audio Visual Interleaved (AVI) files are one of the more popular animated image formats in use today AVI image data can be stored uncompressed, but is typically compressed using a codec. To play an AVI file compressed with a specific codec, that codec must be available on the target system. AVI files can optionally contain audio data and are not limited to 256 colours

MPEG MPEG generally produces better quality video than competing formats, such as Video for Windows, Indeo and Quicktime. MPEG files can be decoded by special hardware or by software. MPEG uses a type of lossy compression, since some data is removed. But the diminishment of data is generally imperceptible to the human eye. MPEG4 - can reduce the size of the file by a factor of 12

MOV Quicktime is the multi-platform industry standard multimedia architecture used by software tool vendors and content creators to create and deliver synchronized graphics, sound, video, text and music. MPEG compresses things very tightly, and to be used you need either extremely powerful hardware or a hardware decoder card. Software-only decoders tend to be too slow at playback

AnimationAnimation

• A series of still images that have been manipulated to give the appearance of movement or life like motion

• the frame rate determines the persistence of vision and smoothness of image to the user

• 30 frames/sec refresh rate (flicker free)• 25 f/s PAL• 24 f/s Movies• 12 f/s Cartoons• 8 f/s minimum

• when the animation speed matches the refresh rate of the screen, the image is flicker free

Cell-Based AnimationCell-Based Animation

• Creation of individual images in cells (frames) which when played produces motion

• this type of animation is the traditional method

Path-Based AnimationPath-Based Animation

• The start and end point and path for the object to follow are defined by vectors

• the background is fixed

• saves memory and processing time especially if the image is an object

TweeningTweening

• The process of taking two images of an animation and producing intermediate images so that the animation appears smooth

Effects - MorphingEffects - Morphing

• The process of transforming an image into a new image that is different to the start image

• especially in terms of the shape of objects

Effects - WarpingEffects - Warping

• The distortion of an image by mathematical processes

Effects - DynamicEffects - Dynamic

• Time of day / time of year animations• this shows changes in lighting (especially sun impact) over the day or changes over the year at a fixed time of day

• Walk-through animations• this shows a scene from a succession of different view points creating the illusion of motion through the scene

• Feature animation• this modifies scene attributes dynamically• it can also be used to let objects in a scene appear or disappear by manipulating their transparency• this is achieved by rendering several variations of a scene and interpolating the resulting images

Effects - Dynamic...Effects - Dynamic...

• Geometry animation• this is the most complex • requires changing the geometric elements of a scene dynamically• this technique has been used in pictures like “Terminator II”, “Jurassic Park”, “Toy Story” and many others• this is what most people refer to when using the term animation

Compression strategies can take Compression strategies can take advantage of 4 kinds of redundancyadvantage of 4 kinds of redundancy

• Coding Redundancy• relies on the fact that not all data will occur with the same probability• compression algorithms also use the fact that it is likely that the same data will often repeat

• Spatial Redundancy• occurs because pixels which are near each other are likely to be similar to each other

• Temporal Redundancy• occurs because pixels in consecutive frames of a video are likely to be similar• MPEG takes advantage of this

• Psychovisual Redundancy• occurs because the human visual system is better at seeing changes in luminance (brightness) than in seeing the changes in chrominance (colour)

Information Processes - CollectingInformation Processes - Collecting

• Collecting involves data being obtained from a variety of sources

• text and number are gathered digitally

• video, audio, images are gathered via analog means and then interpreted into digital form

Information Processes - OrganisingInformation Processes - Organising

• The way information is organised in multimedia product is through storyboarding and screen design

• when organising there are some steps which need to be followed:

• determine the intended audience• create a storyboard• plan your navigational tools• create an aesthetically appealing production

Information Processes - AnalysingInformation Processes - Analysing

• Through the analysis stage, data is turned into useful information

• it involves the testing and retesting of the multimedia presentation

• different design methods can also be applied such as top-down design

Information Processes - Storing / Information Processes - Storing / RetrievingRetrieving

In this information process some things need to be determined such as:• initially, data may be stored and collected in analog from such as videos, audio tape, etc• elements may also be stored digitally such as hard drives, CD-ROMs, DVD Flash media, tape drives etc.• what type of compression techniques will be used• how will it be distributed, CD-ROM, DVD due to high level of production rate• Will it require Internet distribution?

Information Processes - ProcessingInformation Processes - Processing

• Processing is the manipulation of data

• the individual components that will be included into a multimedia presentation need to be processed before being organised by the multimedia software

• In this information process, all the elements need to be processed, ie. Animations created, text formatted, sound and video being edited and compressed via CODEC’s

Information Processes - Information Processes - Transmitting and ReceivingTransmitting and Receiving

• Multimedia delivery is an important decision

• it must be decided whether it will be delivered via CD-ROM, DVD or the Internet

• depending on the decision, access speed, bandwidth and other infrastructure will need to be considered

Information Processes - DisplayingInformation Processes - Displaying

• Displaying needs to be considered at both the hardware level and the software level• the method of projection needs to be considered• will the production be projected, use head up displays, touch screens etc?• will the production fit on the display, ie. Navigation, features etc• in terms of software, what will the ‘run-time engine’ be?• If delivered on the internet, what is the lowest common denominator for “plug-ins”?

Hardware demands by multimedia

The hardware of a multimedia system places limitsOn the quality and size of the multimedia product thatCan be produced or displayed.


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Calculate the size of the following graphics (answer in Kb to the nearest whole number):1. A black and white graphic with a resolution of 640 by 480 and 2 tones2. A colour graphic with a resolution of 1024 by 768 and 64 colours3. A colour graphic with a resolution of 1600 by 1200 and 256 colours4. An 8 bit colour graphic with a resolution of 1280 by 10245. A 32 bit colour graphic with a resolution of 1152 by 864


Calculate the size of the following audio files (answer in Mb, correct to 2 decimal places):1. Sampling rate of 22.05 kHz with a 8 bit sound for 2 minutes in stereo2. Sampling rate of 44.1 kHz with a 16 bit sound for 3 minutes in stereo3. Sampling rate of 22.05 kHz with a 16 bit sound for 1 minute in mono4. Sampling rate of 11 kHz with a 8 bit sound for 4 minutes in mono5. Sampling rate of 44.1 kHz with a 16 bit sound for 10 minutes in stereo

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HSC Multimedia

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