1. 4.1 Digital Multimedia Elements
Graphics
Audio
Video

2. 4.1 Digital Multimedia Elements
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. 2

3. 4.1 Digital Multimedia Elements
Graphics
Bitmaps
Colour depth (bits per pixel) = 1
Number of colours that can be displayed = 21 = 2
File size = 1.3 MB
Comparison of images in different colour depths 3

4. 4.1 Digital Multimedia Elements
Graphics
Bitmaps
Colour depth (bits per pixel) = 8
Number of colours that can be displayed = 28 = 256
File size = 10.3 MB
Comparison of images in different colour depths 4

5. 4.1 Digital Multimedia Elements
Graphics
Bitmaps
Colour depth (bits per pixel) = 24
Number of colours that can be displayed = 224 = 16,777,216
File size = 30.8 MB
Comparison of images in different colour depths 5

6. 4.1 Digital Multimedia Elements
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. 6

7. 4.1 Digital Multimedia Elements
Graphics
Bitmaps
Resolution
72 ppi, 99 KB
150 ppi, 351 KB
300 ppi, 1,333 KB
Comparison of images with different resolutions 7

8. 4.1 Digital Multimedia Elements
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 8

9. 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. 9

10. 4.1 Digital Multimedia Elements
Graphics
Vector graphics
Bitmap
Vector graphics
Magnification of an image in vector graphic and bitmap format 10

11. 4.1 Digital Multimedia Elements
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) 11

12. 4.1 Digital Multimedia Elements
Graphics
Vector graphics
Details of the original bitmap image (left) are lost when it is represented in vector graphic format (right). 12

13. 4.1 Digital Multimedia Elements
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. 13

14. 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.
Audio type
Bit resolution
Sampling rate (Hz)
Voice over telephone
8-bit
11,025
FM broadcast
16-bit
22,050
Compact disc
44,100
DVD
24-bit
96,000
Characteristics of different types of audio 14

15. 4.1 Digital Multimedia Elements
Audio
Audio file with 16-bit resolution
and 44 kHz sampling rate
Audio file with 8-bit resolution and 44 kHz sampling rate
The smooth 16-bit waveform indicates that it has a better quality than the jagged 8-bit waveform. 15

16. 4.1 Digital Multimedia Elements
Audio
Audio file with 8-bit resolution
and 44 kHz sampling rate
Audio file with 8-bit resolution and 11 kHz sampling rate
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. 16

17. 4.1 Digital Multimedia Elements
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. 17

18. 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.
Videos can be played by using Windows Media Center. 18

19. 4.1 Digital Multimedia Elements
Video
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-1
DVD: MPEG-2
iPod and PlayStation Portable: MPEG-4
Streaming video on the Internet: WMV and RealMedia
Colour depth
Number of bits used to represent a pixel
VCD: 24 or 32 bits
DVD: 24 or 32 bits
Factors affecting the size of a video file 19

20. 4.1 Digital Multimedia Elements
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. 20

21. 4.1 Digital Multimedia Elements
Video
WMV
File size = 40 MB
Frame size = 320 × 240 pixels
Frame rate = 25 fps
Uncompressed AVI video clip
File size = 300 MB
Frame size = 720 × 576 pixels
Frame rate = 30 fps
MPEG-1 (VCD)
File size = 52 MB
Frame size = 352 × 288 pixels
Frame rate = 25 fps
Video files can be compressed into different video file formats for different playback media. 21

22. 4.1 Digital Multimedia Elements
Video
MPEG-2 (DVD)
File size = 180 MB
Frame size = 720 × 576 pixels
Frame rate = 25 fps
Uncompressed AVI video clip
File size = 300 MB
Frame size = 720 × 576 pixels
Frame rate = 30 fps
MPEG-4 video clip
File size = 45 MB
Frame size = 320 × 240 pixels
Frame rate = 30 fps
Video files can be compressed into different video file formats for different playback media. 22

23. 4.1 Digital Multimedia Elements
Video
MPEG-2 (DVD)
File size = 180 MB
Frame size = 720 × 576 pixels
Frame rate = 25 fps
Uncompressed AVI video clip
File size = 300 MB
Frame size = 720 × 576 pixels
Frame rate = 30 fps
MPEG-4 video clip
File size = 45 MB
Frame size = 320 × 240 pixels
Frame rate = 30 fps
Video files can be compressed into different video file formats for different playback media. 23

24. 4.2 Analogue Data and Digital Data
Characteristics of 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 such
as CD-ROM and flash memory for long term storage.
Comparison of the characteristics of analogue data and digital data

25. 4.2 Analogue Data and Digital Data
Characteristics of analogue data and digital data
Characteristic
Analogue data
Digital data
Efficiency on
transmission
High rate of transmission error
Low rate of transmission error
Accuracy of
information
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.
Comparison of the characteristics of analogue data and digital data

26. 4.2 Analogue Data and Digital Data
Characteristics of 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

27. 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.

28. 4.2 Analogue Data and Digital Data
Applications of digital data in IT
Workstation A
Workstation B
Hard copy
Computer
network
Transfer data
Output copy
Transfer data
Duplicate
Store data
Transfer processed data
Digital camera
Hard disk
CD-R
Printer
Daily-life applications of digital data

29. 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

30. 4.2 Analogue Data and Digital Data
Sampling
The process of obtaining discrete sample data from the continuous analogue signal for every fixed time interval
Sampling an analogue signal

31. 4.2 Analogue Data and Digital Data
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.
Quantizing an analogue signal

32. 4.2 Analogue Data and Digital Data
Conversion between analogue data and digital data
Original analogue photograph
Sample data obtained from the analogue photograph
Digital code representation of sample data
Digitizing an analogue photograph

33. 4.2 Analogue Data and Digital 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

34. 4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Audio
Speakers
Monitor
Microphone
System unit
Keyboard
Mouse
Standard configuration of a computer system for audio recording and playback

35. 4.2 Analogue Data and Digital Data
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.

36. 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

37. 4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Image
Image type Setting
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
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
File format
recommended
BMP
JPEG
Compression No
Yes
Typical settings for image scanning

38. 4.2 Analogue Data and Digital Data
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.
Conversion of an image from an analogue to a digital format

39. 4.2 Analogue Data and Digital Data
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. 39

40. 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 40

41. 4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Video
TV tuner card
TV tuner box
A TV tuner box (left) and a TV tuner card (right) 41

42. 4.2 Analogue Data and Digital Data
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 42

43. 4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Video
Typical video setting for a web cam File format: compressed AVI Frame size: 320 × 240 pixels Frame rate: 12 fps
Typical video setting for a digital video camera File format: MPEG-1 Frame size: 352 × 288 pixels Frame rate: 25 fps
Examples of different digital video file formats 43

44. 4.2 Analogue Data and Digital Data
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. 44

45. Charge-coupled device (CCD)
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Video
Digital video camera
Charge-coupled device (CCD)
A digital video camera (left) and a charge-coupled device (CCD) (right) 45

46. Charge-coupled device (CCD)
4.2 Analogue Data and Digital Data
Conversion of analogue multimedia elements
Video
Digital video camera
Charge-coupled device (CCD)
A digital video camera (left) and a charge-coupled device (CCD) (right) 46