1. Digital Media
Dr. Jim Rowan
Chapter 2

2. First, some mac software you will be using (found in the application folder)
Grab - used to do a screen capture
TextEdit - used as a simple word processor
PhotoBooth - used to take your picture with the built in camera and take video with the built in camera
Preview: Change image file formats

3. About file formats and extensions (like .au, .doc, .ppt, .mov)
Indication to us (the humans) what kind of file this is
Some software looks at the extension
so... some software will try to open files with improper extensions
results in “file corrupted” error message
try it... change the extension from .doc to .jpg

4. File formats and extensions
Some software looks at the data in the file for more definitive answer (the header)
important file-related information is encoded in the data of the file
for example: some image formats have color tables to reduce the size of the file
some video just saves the changes from one frame to the next
we’ve seen the header before when we used hexFiend to look at images… image size is stored in the header

5. The Question: How do you put stuff in a computer
so that you can manipulate it
so that you can send it
so that someone else can see and use it?
How do you represent the real world in a digital world?

6. The answer: Represent the real world as numbers Store the numbers
Transmit the numbers
Retrieve the numbers
Display them in a form humans understand

7. Today: Overview of things to come… About the real world
About digital representation

8. From the first day’s lecture we saw different types of real world stuff as a bunch of numbers

9. Note on paper

10. Picture

11. Song: fieldsOfGold.mp3

12. Video

13. So… it’s all just numbers, and binary numbers at that
So… it’s all just numbers, and binary numbers at that! First we must talk about numbering systems!

14. First, Numbering systems: Decimal Binary Hexadecimal

15. Which statement is True?
5 + 5 = = = 10 F + 1 = 10

16. welcome to numbering systems!
well… it depends…
5 + 5 = 10 (in decimal) = 10 (in binary) = 10 (in octal)
welcome to numbering systems!

17. Numbering systems Humans: decimal Computers: binary
Humans: 10 fingers, 10 digits
0, 1, 2, 3, 4, 5, 6, 7, 8 & 9 10
Computers: binary
Computers: 1 finger, 2 digits
0 & 1

18. Hexadecimal Humans and Computers: hexadecimal
Hexadecimal: 15 fingers, 16 digits
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

19. Why Hexadecimal?
You can use one hexadecimal instead of 4 binary digits
While this seems complicated.. it is actually easier (after some practice!) for humans to deal with 16 different digits than 4 0s and 1s
In Hex: ABCDEF
In binary:

20. How many different things?
In Decimal 1 digit can represent 10 different things:
In Decimal 2 digits can represent 100 different things: …
In Binary 1 digit can represent 2 different things:
0 and 1
In Binary 2 digits can represent 4 different things:
In Hexadecimal 1 digit can represent 16 different things:
A B C D E F
In Hexadecimal 2 digits can represent 256 different things:
A 0B 0C 0D 0E 0F A 1B 1C 1D 1E 1F 20 21… F9 FA FB FC FD FE FF

21. How many different things?
So… how many things can you count with 4 hex digits?
USE THE FORMULA!
[number of digits in the numbering system]**[number of digits used]…
[16]**[4] = 65,536
How many things can you count with 4 decimal digits?
[10]**[4] = 10,000
How many things can you count with 4 binary digits?
[2]**[4] = 16

22. Counting… with a different number of fingers (it’s the same process but different number sets)
10 fingers: Counting in decimal
0, 1, 2, 3, 4, 5, 6, 7, 8, 9 then… start over with 0 and increment the digit to the left ==> 10
1 finger: Counting in binary
0, 1 then… start over with 0 and increment the digit to the left ==> 10
16 fingers: Counting in hexadecimal
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F then… start over with 0 and increment the digit to the left ==> 10

23. Binary Coding Data for a computer... Binary Data for humans... Hex
zeros and ones
Data for humans... Hex
1 Hexadecimal represents 4 binary digits
Data for humans… ASCII (the alphabet)
2 hex codes ==> 1 ASCII code
For example ==>

24. Example: ASCII Code Humans and Computers: ASCII
The ASCII code for C is
in hexadecimal: 43 (In decimal: 67)
which is binary:

25. Stuff in the Real World to Stuff on a computer… HOW?
A note…
Letters of the alphabet-> bits (0s and 1s)
A picture…
Reflected light -> bits (0s and 1s)
A song…
Pressure waves in air -> bits (0s and 1s)
A video…
Pressure waves in air and Reflected light ->
bits (0s and 1s)

26. HOW? After numbering systems we need to know a bit about the real world, about: Discrete & Continuous

27. Phenomena in the Real world: discrete vs continuous
Things in the real world can be discrete
They either ARE or they ARE NOT
These things can be counted
Examples:
The number of cars in the parking lot
The number of beans in a jar

28. Phenomena in the Real world: discrete vs continuous
Things in the real world can be continuous
Continuous can’t be counted, it must be measured
Examples:
Atmospheric pressure
Height of an ocean wave
Frequency of a sound wave

29. The problem is... computers can only count
Discrete data is easy for a computer
count it and store it as a number
Continuous data... easy? not so much
music:
sample the music and then…
encode as a collection of numbers
pictures:
measure the amount (intensity) and frequency of light (color) in a number of spots of light (pixels)
encode the frequency and the intensity as a collection of numbers

30. Question... If computers only store 0s and 1s...
How does all this continuous stuff end up in a computer so that we can save it and play it back?
Answer
Continuous data must be converted to discrete data through sampling

31. From the Real World …and Back!
Converting continuous phenomenon to digital data:
-You must SAMPLE to convert it to discrete
Sampling consists of two processes
1) stop to take a measurement
the number per time period is called the sample rate
2) take and store the measurement
the number of different values each sample can take on is called the quantization level
Digital data back to continuous phenomenon:
Display samples using “sample and hold”
Play the sample for the duration of the sample time

32. Sampling… more on this a bit later…
there’s other stuff to consider before we jump into sampling

33. Before we go further with sampling: What this stuff means:
Bit: binary digit Byte: 8 Bits KB: kilo byte (1000 bytes) MB: mega byte (1,000,000 bytes) GB: giga byte (1,000,000,000 bytes) TB: tera byte (1,000,000,000,000 bytes) KBPS: kilo (1,000) bits per second MBPS: mega (1,000,000) bits per second

34. A note to the Geeks…
The rest of you guys… pay no attention to this slide… it’ll just upset you!
Yes, I know that within the world of computers 1K is not 1000 but is 1024
For this class let’s just lie to the rest of the folks and keep it to ourselves!

35. Also… note this!
Communications are usually stated in bps (bits per second)
File size is usually stated in bytes
AND: there are 8 bits per byte
you will have to convert from one to the other when you do download/upload calculations

36. A bit about network access
dial up connection
ADSL T1 T3

37. Network access... dial up connection phone modem asymmetric
56,000 bps (bits, not bytes) max downstream (internet to modem)
33.6 kbps upstream (modem to internet)
rarely get these speeds

38. Network access... ADSL asymmetric digital subscriber line
over copper phone wires
limited to short distance from phone switch
asymmetric
6.1 mbps downstream
640 kbps upstream

39. Network access... Commercial internet users
T1 connection mbps
T3 connection 44.7 mbps
Provide web servers for others to put websites on
Large commercial enterprises will have their own web server

40. Time-to-download/upload calculations
The Speeds:
Dial-Up
56,000 bps internet to modem (downstream)
33,600 bps modem to internet (upstream)
ADSL
6.1 mbps (million bps) downstream
640 kbps (thousand bps) upstream T1
1.544 mbps T3
44.7 mbps
NOTE!
bps is bits per second while filesize is stated in bytes

41. And now for a little SAMPLING!
Sampling is the process of looking at stuff VERY frequently then taking a measurement and storing the measurement

42. Next class… sampling!

43. But. How many samples do you need
But... How many samples do you need? It depends… So let’s look at sampling…

46. single sample

47. single sample

48. single sample (sample and hold)

49. two samples

50. two samples

51. two samples (sample and hold)

52. three samples

53. three samples

54. three samples (sample and hold)

55. four samples

56. four samples

57. four samples (sample and hold)

58. five samples

59. five samples

60. five samples (sample and hold)

61. Taking it a lot farther…

62. Taking it a lot farther…

63. How frequently should I sample?
too few
small file size (good)
not a faithful representation when replayed
too many
large file size (bad)
excellent representation when replayed
The Nyquist rate
twice as many samples as the frequency being captured
Results in an ok file size
Results in faithful representation when replayed

64. CD quality is 44,100 samples per second
Why?
Human hearing response is in the range of 20 to 22,000 cycles per second
Nyquist sample rate =
highest frequency to be captured = 22,050 CPS
2 x 22,050 = 44,100 samples per second

65. Looking at FieldsOfGold.mp3…
4 minutes and 59 seconds long
1,201,173 bytes in length
Can this be right?
CD quality
44,100 samples per second (sample rate)
16 bit samples (quantization level is 16 bit)
16 bits can store 65,536 different levels
(2**16 = 65,536 individual levels)

66. FieldsOfGold.mp3 4’59 = 299 seconds long
299 x 44,100 samples per second
= 13,156,000 samples
13,185,900 x 2 bytes/sample (2 bytes = 16 bits)
26,371,800 bytes
Stereo: 2 channels => 52,743,600 bytes
Should be 52+ megabytes!
Why does it show only 1.2 megabytes?
HMMMmmm...

67. FieldsOfGold.mp3
Why 52+ megabytes not 1.2 megabytes?
wait for it…

68. FieldsOfGold.mp3 Why 52+ megabytes not 1.2 megabytes? This is an MP3!
The data is COMPRESSED!
If you had the song on a CD it would be 52+ megabytes long and in .aiff format

69. Two types of compression
Lossy
Lossless
run length encoding
table compression
.mp3 audio
.jpeg images

70. Further reading http://en.wikipedia.org/wiki/Nyquist_rate

71. The side effects of sampling: sampling artifacts Sampling Artifacts are the negative side effects caused by having to sample continuous data

72. Sampling Artifacts
Under-sampling: not enough samples being taken of continuous data can produce undesired artifacts
Examples might be:
Moire’ patterns on images
retrograde motion on video

73. Sampling Artifacts (cont.)
Not enough quantization levels when sampling continuous data can produce undesired artifacts
Examples might be:
too few grey levels: gradients become steps
too few brightness levels: posterization

76. Sampling Artifacts
Retrograde Motion
4 samples/cycle, 2 cycles
2 samples/cycle, 2 cycles

77. Sampling Artifacts (cont.)
Audio
too few amplitude levels, quantization noise
8 bits (256 amplitude levels) produces discernable noise
16 bits (65,536 amplitude levels) CD quality, no discernable hiss
general sound “fuzziness” or a “flat” sound

78. How can you store an image on a computer?
Bitmapped images
Vector graphics

79. Images, bitmapped Are stored as arrays of pixels
Can be stored directly
TIFF & PNG for example
Can have an associated color map
JPEG for example
Generating these pixels from the stored model is called rendering

84. Images, vector graphic Are stored as mathematical descriptions
Often smaller than bitmapped
Size of the file is independent of resolution or image size
Not suitable for some type of images

85. Example & Comparison Bitmapped graphics
Defined as spots (pixels) of color
Has problems scaling
File size unaffected by image complexity
File size affected by the image size
Vector graphics
Defined by their mathematically described parts
File size affected by image complexity
File size unaffected by the image size
(scaling is easy)

89. Moving images Captured live with camera Generated from animation
iMovie
Stored as video
Generated from animation
Blender
Similar to 2D vector graphics… but in 3D and with a means of creating motion

90. 2110-01&02 for Friday Network communication & Servers and Clients

91. Servers & Clients... Clients consume and display internet content
Your browser is a client
Clients request content from servers
by sending a server an message which is a request for a web page
Servers respond to requests for internet content
send requested web pages to Clients
The content is sent in HTML code
HTML sent by the server is interpreted by the client (browser) and displayed on your display
Look at and view source

92. URL (uniform resource locator)… a human-readable name
URL takes the form:
URL has 3 parts
the protocol that you are using (
The domain name: (
The directory and file you want to see: (newStuff.index.html)
the URL maps to a number called an IP
address

93. Servers & Clients... servers have fixed IPs so they are easy to find
your computer probably uses DHCP which is a dynamic (changing from connection to connection) IP
An example: my IP right now (assigned through dhcp) is: (look it up in system preferences)
IPv4 vs IPv6

94. requested
webpages
DHCP:
your browser
(Safari)(client)
yahoo.com
(server)
your computer
The Internet
walmart.com
(server)
Domain Name System (DNS)

95. requested
webpages
DHCP:
your browser
(Safari)(client)
yahoo.com
(server)
your computer
ISP
The Internet
walmart.com
(server)
Domain Name System (DNS)

96. requested
webpages
DHCP:
your browser
(Safari)(client)
yahoo.com
(server)
your computer
The Internet
walmart.com
(server)
Domain Name System (DNS) =

97. requested
webpages
/index.html
DHCP:
your browser
(Safari)(client)
yahoo.com
(server)
your computer
The Internet
walmart.com
(server)
Domain Name System (DNS) =

98. Questions?