1. Specialised Module 4: Materials
Industrial Technology: Multimedia Year 10
Sunday, 11 November 2018

2. Materials: Outline
the properties of multimedia elements in relation to file size, storage and delivery of multimedia presentations.

4. Multimedia Systems
Multimedia systems combine different types of media into interactive information systems.
Most multimedia is distributes using CD, DVD and the Internet (due to increases in the bandwidth).

5. Multimedia Systems
multimedia systems – information systems that include combinations of the following media, including:
– text and numbers
– audio
– images and/or animations
– video
– hyperlinks

6. Text & Numbers

7. Text & Numbers
Most information is presented using text and the images, sound, video and other media are used to reinforce the textual information.

8. Text & Numbers
Numbers are less commonly used expect as part of the underlying code that controls presentations. For example the selection of a radio button is commonly stored as a number (internally).

9. Text & Numbers
Where numbers are used to display information, they are commonly represented as text rather than numeric values.

10. Text & Numbers Two methods of representing text are:
ASCII – American Standard Code of Information Interchange such as Unicode.
EBCDIC – Extended Binary Coded Decimal Interchange Code.

11. Text & Numbers
Standard ASCII uses 7 bits to represent each letter (0 to 127).
Unicode extends this to include characters from other languages as well as various special characters.

12. Text & Numbers The number media type is used to represent:
Integers (whole numbers)
Real numbers (decimals)
Currency
Boolean (true/false)
Dates and time.

13. Text & Numbers
In multimedia systems both text and numbers are displayed as images using fonts.
The font describes how each character will be rendered when displayed.

14. Text & Numbers Two types of fonts:
Outline fonts – Example is True Type. These fonts typically describe each character using mathematical descriptions of the lines and curves.
Raster fonts – simply stores a bitmap of each character.

15. Text & Numbers Two methods of compression:
Run Length Encoding (RLE)
Huffman
Both are examples of lossless compression, meaning no data is lost during compression and decompression.

16. Hyperlinks
Hypertext describes bodies of text that are linked in a non-sequential manner.

17. Hyperlinks
Hypermedia is an extension of hypertext to include links to a variety of different media types including images, audio and video.

18. Hyperlinks
The organisation of hypertext and hypermedia is based on hyperlinks.

19. Hyperlinks
In multimedia presentations, hyperlinks are constructed to transfer the user from one section to another.

20. Hyperlinks – HTML Tags

21. Hyperlinks – HTML Tags
The start of the tag for a hyperlink commences (begins) with <a,
Followed by the href = , then the URL to the required content (video, image, html page etc) within double quotes.
Finally the end bracket >.
< a href=“ >

22. Hyperlinks – HTML Tags
Following the > is the text or image to which the hyperlink is applied (the red text).
The end tag </a> finalises the hyperlink.
< a href=“ > Parramatta Education Centre </a>

23. Audio
Used to represent sounds; this includes music, speech and sound effects.

24. Audio
All sounds are transmitted through the air as compression waves (vibrations in the air).

25. Audio
The sound waves is the data and what we recognise as sound is the information.

26. Audio
Formats include: MP3, Wav, WMA and MID (represents individual notes).

27. Audio Two essential components:
Frequency – measured in hertz (Hz) and is the number if times per second that a complete wavelength occurs.
Amplitude – determines the volume or level of the sound (height of the wave). Measured in decibels (db).

28. Audio – Sampled Audio
The level, or instantaneous amplitude, of the signal is recorded at precise time intervals.

29. Audio – Sampled Audio
This results in a large number of points that can be joined to approximate the shape of the original sound wave.

30. Audio – Sampled Audio
Two factors that influence the accuracy and quality:
Number of samples
Bits used per sample

31. Audio – Sampled Audio
Example: Audio on a CD contains samples per second for both left and right channels and each sample is 16 bits long.

32. Audio – Sampled Audio
This means an audio track that is 5 minutes long requires storage of samples x 300 secs x 16 bits per sample x 2 channels = 50MB.

33. Audio – Sampled Audio
MPEG (Moving Picture Expert Group) sets standards for compression of both audio and video.

34. Audio – Sampled Audio MP3 is the most popular for audio.
MP3 is lossy compression which means some of the original is lost during compression.
Removes sounds that will not be noticed by the human ear.

35. Audio – Sampled Audio
Removes frequencies out of the human hearing range and quiet background sounds imperceptible to most humans.

36. Audio – Individual Notes
Each note or tone in the music is represented in terms of its pitch (frequency) and its duration (time).
Further information can be specified such as how the note starts and ends.

37. Audio – Individual Notes
Most common storage is MIDI (Musical Instruments Digital Interface) format.

38. Images Used to represent data that will be displayed visually.
Two techniques for representing images:
bitmap – JPEG, GIF, PNG and BMP
vector – SVG, WMF and EMF

39. Images – Bitmap
Represent each element or dot (pixel) in the picture separately.
For 256 colours, 8 bits are required for each pixel.

40. Images – Bitmap The number of bits per pixel is called the bit depth.
The higher the bit depth = the more colours = the more storage required.

41. Images – Bitmap

42. Images – Bitmap

43. Images – Bitmap
Resolution determines how clear or detailed the image appears.
Expressed as the number of horizontal pixels time the vertical pixels.

44. Images – Bitmap - Storage
For example if an image has a resolution of 800 by 600 then total number of pixels is 480,000.
If the bit depth is 24 bits then each pixel requires 3 bytes of storage.

45. Images – Bitmap - Storage
Therefore the total file size in bytes will be 480,000 time 3 bytes = 1,440,000 bytes.
Convert to kilobytes by diving by and then to megabytes, by again dividing by 1024 means the total size = 1.37 MB

46. Images – Vector Represent each portion of the image mathematically.
Uses a mathematical description of each shape that makes the final image.

47. Images – Vector
Less storage then a bitmap but more processing needed to transform the data into an image.

48. Images – Vector
Can be resized without loss of quality and without increasing the size of the data used to represent the image.

49. Images – Vector
Not suited for photographic images –the detail required is difficult and inefficient to reproduce mathematically.

50. Animation
Is achieved by displaying a sequence of images, known as cels or frames, one after the other.

51. Animation
If the images are displayed at a sufficient speed then the human brain merges the images together in such a way that we perceive continuous movement (24 frames per second).

52. Animation
Prior to computer animation each image was drawn on a sheet of clear celluloid material. This allowed a single background image to be reused by overlaying each cell in turn. This process is called “onion skinning”.

53. Animation
Tweening – key frames are drawn (by hand or using image tools) and then the tweening function (animator) produces a sequence of intermediate cells that progressively alter the first key frame into the second key frame.

54. Animation
Cel-based – a sequence of cels (images) with small changes between each cel. When played the illusion of movement is created.

55. Animation
Path-based – a line (path) is drawn for each character to follow. When played each character moves along their line in front of the background.

56. Video
Combines image and sound data together to create information for humans in the form of movies or animation.

57. Video
Most movies are recorded at 24 frames per second (fps).

58. Video – Raw Video
Consider 1 minute of raw video; if there are 24 fps then 1440 frames or bitmaps are needed (1 minute – 24 x 60).

59. Fact
“Toy Story” took 46 days of continuous processing to render (draw) the film’s 110,000 frames at a rate of about 1 frame every 1 to 3 hours.

60. Video – Raw Video
If each bitmap has a resolution of 640 x 480 and each pixel is represented by 3 bytes (24 bit) then a minute of video requires a staggering 1,327,104,000 bytes (1.2 GB) of storage.

61. Video – Raw Video Total Frames = 24 x 60 secs = 1400 frames
Data/Frame = 640 x 480 pixels x 3bytes = bytes
Total Storage = 1400 frames x = bytes = 1.2 GB

62. Video – Compression
Compressing standards were formed to reduce the amount of storage needed.
Moving Picture Experts Group (MPEG) is a set of standards for compression.
Formats include: MPG, MOV, AVI and WMV.

63. Video – Compression
Most common technique used to compress video data is known as ‘block based coding’.

64. Block Based Coding Coding process:
Current frame is split up into a series of blocks; each block contains a set number of pixels
Content of each block is then compared with the same block in a past frame.

65. Block Based Coding Coding process:
If the block in the past frame is a close match then presumably no motion has occurred, and a zero vector is stored as an indicator.
Should the blocks not match then other like sized blocks, in the past frame, within the general area are examined for possible matches.

66. Block Based Coding Coding process:
If a match is found then a vector is stored indicating the change in position of the block.
If no match is found then the block in the current frame must be stored as a bitmap.