4.1 digital multimedia elements graphics audio video
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Graphics Bitmaps
A bitmap image is a collection of colour dots called pixels arranged in rows and columns.
A pixel is the smallest picture element that can be shown on a computer screen.
The number of colours can be displayed in a pixel is determined by the number of bits used to represent the pixel (known as colour depth).
The larger the colour depth, the larger the number of colours can be displayed in the image.
4.1 Digital Multimedia Elements
4.1 Digital Multimedia Elements Graphics
Bitmaps
Comparison of images in different colour depths
Colour depth (bits per pixel) = 1Number of colours that can be displayed = 21 = 2File size = 1.3 MB
4.1 Digital Multimedia Elements Graphics
Bitmaps
Comparison of images in different colour depths
Colour depth (bits per pixel) = 8Number of colours that can be displayed = 28 = 256File size = 10.3 MB
4.1 Digital Multimedia Elements Graphics
Bitmaps
Comparison of images in different colour depths
Colour depth (bits per pixel) = 24Number of colours that can be displayed = 224 = 16,777,216File size = 30.8 MB
Graphics Bitmaps
Resolution Is the measurement of the number of pixels per unit
length in a bitmap image.
Is measured by pixels per inch (ppi). The higher the resolution, the more details of the image
can be shown. But the file size of an image will increase dramatically.
4.1 Digital Multimedia Elements
4.1 Digital Multimedia Elements Graphics
Bitmaps Resolution
Comparison of images with different resolutions
72 ppi, 99 KB
150 ppi, 351 KB
300 ppi, 1,333 KB
Graphics Bitmaps
Digital images for screen display are usually stored at a resolution ranging from 72 to 95 ppi.
For photograph printing, the images can be stored at a resolution ranging from 200 ppi to 400 ppi.
Common file formats of bitmap BMP JPEG GIF
4.1 Digital Multimedia Elements
Graphics Vector graphics
They are composed of a number of objects. A vector object can be a shape, a line or a string of text. The shape and location of vector objects are defined by
mathematical formulae. Can rescale and modify every detail of each vector object
easily without affecting the quality of vector graphics.
4.1 Digital Multimedia Elements
Graphics Vector graphics
4.1 Digital Multimedia Elements
Bitmap
Vector graphics
Magnification of an image in vector graphic and bitmap format
Graphics Vector graphics
The file size of vector graphics does not grow rapidly even when more and more vector objects are drawn in the image.
The file size of vector graphics is usually much smaller than that of a bitmap image.
They suit for representing simple charts, line arts and illustrations.
They are not suitable for representing images with complicated colour patterns.
Examples of popular vector graphic formats Windows Metafile (WMF) Shockwave Flash (SWF) Postscript (EPS)
4.1 Digital Multimedia Elements
Graphics Vector graphics
4.1 Digital Multimedia Elements
Details of the original bitmap image (left) are lost when it is represented in vector graphic format (right).
Audio Audio files in a computer are the digitized data of music,
speech and any kind of audio signals. The quality of a digital audio file is determined by its bit
resolution and sampling rate. Bit resolution
Is the number of bits used to represent the amplitude of an audio signal.
The higher the number of bits used, the more precise the amplitude of the audio signal will be.
4.1 Digital Multimedia Elements
Audio Sampling rate
Is the number of samples taken each second during the conversion process
Is measured in Hz. The higher the sampling rate, the better the quality of the
digital audio will be.
4.1 Digital Multimedia Elements
Audio type Bit resolution Sampling rate (Hz)
Voice over telephone
8-bit 11,025
FM broadcast 16-bit 22,050
Compact disc 16-bit 44,100
DVD 24-bit 96,000Characteristics of different types of audio
Audio
4.1 Digital Multimedia Elements
The smooth 16-bit waveform indicates that it has a better quality than the jagged 8-bit waveform.
Audio file with 16-bit resolution
and 44 kHz sampling rate
Audio file with 8-bit resolution
and 44 kHz sampling rate
Audio
4.1 Digital Multimedia Elements
The 44 kHz audio file contains more samples to represent the original audio signal and therefore it is more precise than the 11 kHz audio file.
Audio file with 8-bit resolution
and 44 kHz sampling rate
Audio file with 8-bit resolution and 11 kHz
sampling rate
Audio Stereo audio contains two streams of audio signals,
known as left sound track and right sound track. Mono audio contains only one sound track. Audio data can be stored either in uncompressed or
compressed format. WAV is the most popular type of uncompressed audio file
format. WMA and MP3 are examples of compressed audio widely
used in portable music players and web pages.
4.1 Digital Multimedia Elements
Video Is a sequence of full-motion images together with sound
tracks. The file size of it can be very large.
4.1 Digital Multimedia Elements
Videos can be played by using Windows Media Center.
Video
4.1 Digital Multimedia Elements
Factor Description Example
Frame size
Number of horizontal and vertical pixels on each video picture (frame)
Frame size for VCD-PAL is 352 × 288 pixels. Frame size for DVD-PAL is 720 × 576 pixels.
Frame rate Number of frames displayed per second
Frame rate for both VCD-PAL and DVD-PAL is 25 fps. Frame rate of a MPEG-4 video played in PlayStation Portable is 30 fps.
Duration Play time of a video clip -
Compression
Reduction of quantity of data of video clips by changing the content or the way of representation of video frames
VCD: MPEG-1DVD: MPEG-2iPod and PlayStation Portable: MPEG-4Streaming video on the Internet: WMV and RealMedia
Colour depth
Number of bits used to represent a pixel
VCD: 24 or 32 bitsDVD: 24 or 32 bits
Factors affecting the size of a video file
Video The higher the frame size and frame rate, the better the
video quality and the larger the file size. A particular compression method has its own
specification of compression ratios, frame sizes and frame rates.
Different video file formats require different media players and plug-ins.
AVI is the most popular standard of uncompressed video.
MPEG-1, MPEG-2 and WMV are examples of compressed video file formats.
4.1 Digital Multimedia Elements
Video
4.1 Digital Multimedia Elements
WMVFile size = 40 MBFrame size = 320 × 240 pixelsFrame rate = 25 fps
Video files can be compressed into different video file formats for different playback media.
MPEG-1 (VCD)File size = 52 MBFrame size = 352 × 288 pixelsFrame rate = 25 fps
Uncompressed AVI video clipFile size = 300 MBFrame size = 720 × 576 pixelsFrame rate = 30 fps
Video
4.1 Digital Multimedia Elements
Video files can be compressed into different video file formats for different playback media.
Uncompressed AVI video clipFile size = 300 MBFrame size = 720 × 576 pixelsFrame rate = 30 fps
MPEG-2 (DVD)File size = 180 MBFrame size = 720 × 576 pixelsFrame rate = 25 fps
MPEG-4 video clipFile size = 45 MBFrame size = 320 × 240 pixelsFrame rate = 30 fps
Video
4.1 Digital Multimedia Elements
Video files can be compressed into different video file formats for different playback media.
Uncompressed AVI video clipFile size = 300 MBFrame size = 720 × 576 pixelsFrame rate = 30 fps
MPEG-2 (DVD)File size = 180 MBFrame size = 720 × 576 pixelsFrame rate = 25 fps
MPEG-4 video clipFile size = 45 MBFrame size = 320 × 240 pixelsFrame rate = 30 fps
Characteristics of analogue data and digital data
4.2 Analogue Data and Digital Data
Characteristic Analogue data Digital data
Way of measurement
Continuous signals of amplitude and frequency of the source are measured.
Information is represented in discrete form. In other words, a set of finite numbers of symbols (usually ‘0’ and ‘1’) is used to represent a piece of information
Efficiency on data storage
Low: The physical size of storage media such as cassette tape and video tape are much larger than the corresponding digital storage media. Their life-time is much shorter.
High: Data can be stored in compact media suchas CD-ROM and flash memory for long term storage.
Comparison of the characteristics of analogue data and digital data
Comparison of the characteristics of analogue data and digital data
Characteristics of analogue data and digital data
4.2 Analogue Data and Digital Data
Characteristic Analogue data Digital data
Efficiency ontransmission
High rate of transmission error
Low rate of transmission error
Accuracy ofinformation
Accuracy depends on the sampling technique used.
Lower accuracy: Not all information is converted and recorded in the process of converting analogue signals to digital signals.
Replication
Absolute replication is nearly impossible. Data is lost in the replication process.
Absolute replication and error-free transmission of data are possible and easy.
Characteristics of analogue data and digital data
4.2 Analogue Data and Digital Data
Characteristic Analogue data Digital data
Mode of data access
Mostly sequential access
Direct access is possible, depending on the media used for storage.
Efficiency on data analysis
Low: Analogue content is difficult to search for, analyze and reconstruct to produce other information.
High: Digital contents can be efficiently reused or processed by computers to generate information.
Comparison of the characteristics of analogue data and digital data
4.2 Analogue Data and Digital Data
Applications of digital data in IT All electronic devices including computers and modern
data transmission channels handle data in binary forms.
Digital data and computer programs can be represented in sequences of binary numbers.
This makes operations of electronic devices on digital data such as storage, transmission, manipulation and duplication highly precise and efficient.
Store data Transfer processed data
4.2 Analogue Data and Digital Data
Applications of digital data in ITWorkstation A Workstation B
CD-RDigital camera Hard disk Printer
Hard copy
Output copy
Duplicate Transfer data
Computernetwork
Daily-life applications of digital data
Transfer data
4.2 Analogue Data and Digital Data
Conversion between analogue data and digital data
Digitization is the process of converting analogue data into
digital data. Digitization involves two procedures
Sampling Quantization
Sampling an analogue signal
Sampling The process of obtaining discrete sample data from the
continuous analogue signal for every fixed time interval
4.2 Analogue Data and Digital Data
Quantizing an analogue signal
Quantization The process of converting the attribute of each sample
data into a digital code using a predefined scale The digital code is usually represented by a binary number.
4.2 Analogue Data and Digital Data
Digitizing an analogue photograph
Conversion between analogue data and digital data
4.2 Analogue Data and Digital Data
Sample data obtained from the analogue photograph
Original analogue photograph Digital code representation of sample
data
Conversion of analogue multimedia elements
Audio Sound is inherently analogue. A sound card is an electronic circuit board that is
responsible for conversion. Digital audio files can be stored in a large variety of file
formats, for example, WAV, MP3, WMA and RA. The quality of digital audio is determined by
Sampling rate Bit resolution (number of bits per sample) Number of channels
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Audio
4.2 Analogue Data and Digital Data
Standard configuration of a computer system for audio recording and playback
Mouse
Microphone
Monitor
System unit
Speakers
Keyboard
Conversion of analogue multimedia elements
Audio Since the digital audio is an approximation of the
analogue source, the audio playback cannot be the same as the original one.
However, higher sampling rate and bit resolution can record and reproduce audio output closer to the original one.
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Image Analogue images such as photographs or printed
materials can be converted into digital images using a scanner.
The scanned images are stored as bitmap graphics. The quality of a bitmap graphic is determined by
Resolution Colour depth Compression ratio
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Image
4.2 Analogue Data and Digital Data
Image typeSetting
Plain text and art
line
Black & white photo (for screen
display)
Colour photo (for screen
display)
Colour photo (for high quality
printing)
Resolution 300 ppi 72 ppi 72 ppi 300 ppi
Colour depth
1 bit / pixel (21 = 2 levels: black and white)
8 bits / pixel (28 = 256 levels of grey-scale).
24 bits / pixel (8 bits for Red, Green and Blue Respectively) (224 ≈ 16.8 million colours)
24 bits / pixel (8 bits for Red, Green and Blue respectively) (224 ≈ 16.8 million colours)
Colour mode Halftone Grey-scale RGB RGB
File formatrecommended
BMP JPEG JPEG JPEG
Compression No Yes Yes YesTypical settings for image scanning
Conversion of analogue multimedia elements
Image No matter what the scanning settings are, the scanned
digital image cannot be the same as the original analogue source.
There is always a loss in information during the digitization process.
4.2 Analogue Data and Digital Data
Conversion of an image from an analogue to a digital format
Conversion of analogue multimedia elements
Image Printing a digital image on paper and projecting it on a
screen are examples of conversion of digital images into analogue images.
The colour ranges of different presentation media are different,so the output analogue images deviate from the digital images.
The manufacturing quality of the output devices is another factor affecting the appearance of the output images.
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements Video
To capture television programmes into a computer, we need a TV tuner card to receive TV signals from the antenna.
A TV tuner card converts analogue TV signals into a sequence of digital images and digital audio.
A video capture card works in a similar fashion except that it receives video sources instead of radio frequencies.
Example of video sources Video cassette recorders (VCR) Digital video camera Web cam Digital camera
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements Video
4.2 Analogue Data and Digital Data
TV tuner box
A TV tuner box (left) and a TV tuner card (right)
TV tuner card
Conversion of analogue multimedia elements
Video The quality of a digital video is determined by the frame
size, frame rate and the video compression algorithm. Example of digital video file formats
AVI MPEG-1 MPEG-2 WMV MOV RM
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements Video
4.2 Analogue Data and Digital Data
Typical video setting for a web camFile format: compressed AVIFrame size: 320 × 240 pixelsFrame rate: 12 fps
Typical video setting for a digital video cameraFile format: MPEG-1Frame size: 352 × 288 pixelsFrame rate: 25 fps
Examples of different digital video file formats
Conversion of analogue multimedia elements Video
Modern digital video cameras and web cams contain charge-coupled devices (CCD) used to convert analogue video signals into digital video data in real time.
The captured digital video data can be transferred directly to computers through USB or FireWire (IEEE 1394) ports.
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements Video
4.2 Analogue Data and Digital Data
Digital video camera
Charge-coupled device (CCD)
A digital video camera (left) and a charge-coupled device (CCD) (right)
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