1. ITEC2110, Digital Media Chapter 1 Background & Fundamentals
GGC -- ITEC Digital Media

2. Content Analog vs. Digital Digitization (Sampling & Quantization)
Bits basic concepts
How bits represent information

3. Types of Information
Analog information
Digital information

4. Analog Information (continuous information)
Examples:
time
weight
temperature
Brightness of a light
Loudness of your voice …

5. Accuracy of Analog information: difficult to achieve
How long is the black bar?

6. Digital Information (discrete information)
Examples:
The number of students in this class
The number of cars in the parking lot
The number of characters in your name …

7. Phenomena in the Real world: discrete vs continuous
Things in the real world can be discrete
These things can be counted
Examples:
The number of cars GM produced each year
The number of beans in a jar

8. 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:
Air pressure
Height of an ocean wave
Frequency of a sound wave

9. characteristics of Analog vs. Digital
Analog information
Continuous
Cannot be counted, must be measured
made up of infinite number of data points
Difficult to be accurate
Digital information
Discrete
Countable
Can be Accurate

10. computers can only deal with digital information
Discrete data is easy for a computer
count it and store it as a number
Continuous data
How?

11. 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?

12. Answer
Continuous data must be converted to discrete data

13. Sampling: from continuous to discrete
Converting continuous information to digital data:
-You must SAMPLE to convert it to discrete

14. Sampling rate
the number of samples per time period is called the sample rate

15. Sample and Hold: from digital to continuous
Digital data back to continuous information:

16. Digitization
Digitization is the process of converting analog information into digital data that computers can handle
2-step process:
sampling
quantization

17. Wave height
Wave height

19. single sample

20. single sample

21. single sample (sample and hold)

22. two samples

23. two samples

24. two samples (sample and hold)

25. three samples

26. three samples

27. three samples (sample and hold)

28. four samples

29. four samples

30. four samples (sample and hold)

31. five samples

32. five samples

33. five samples (sample and hold)

34. Taking it a lot farther…

35. Taking it a lot farther…

36. 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

37. 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

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

39. Quantization
Quantization is the process of representing the sample data using only given number of values.
The given number of values determines the bit depth of the quantization.
In other words, bit depth refers to the number of allowable levels you map (or round) the sample data to.

40. Example: 10 levels
For 10 discrete levels, you may have the 10 allowable values as
1, 2, 3, 4, 5, 6, 7, 8, 9, 10
0, 5, 10, 15, 20, 25, 30, 35, 40, 45
2, 4, 6, 8, 10, 12, 14, 16, 18, 20
0, 100, 200, 300, 400, 500,600,700,800, 900
... and so forth

41. Suppose you choose 1,2,3,4,5,6,7,8,9,10
For 1,2,3,4,5,6,7,8,9,10
Any value below 1.0 will be recorded as 1.0.
Any value higher than 10 will be capped at 10.
Any value will be rounded to closest decimal value
It works well if all data fall in this range. But it may not be always the case.

42. Increase Number of Allowable Levels
Will achieve better accuracy when more levels are used for quantization.
However, for digitization, increasing the number of allowable levels (i.e. increasing bit depth) will increase the file size.

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

44. Sampling Artifacts
Under-sampling: not enough samples being taken of continuous data can produce undesired artifacts

45. 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

46. Sampling Artifacts
Retrograde Motion
2 samples/cycle, 2 cycles

47. Sampling Artifacts

48. Sampling rate is related to: Bit depth is related to:
Overview of how sampling rate and bit depth affect digital media file quality
Sampling rate is related to:
Bit depth is related to:
digital images
image resolution, or number of pixels
number of allowable colors in an image
digital video
number of pixels in the video, frame rate
number of allowable colors
digital audio
sampling rate of the audio (it limits how high the pitch of the audio can be captured)
number of allowable levels of amplitude
Details will be covered in chapters for each media type.

49. Now you should be able to answer the following questions
Computers store and transmit information using digital data. What exactly is digital data?
Is there anything not digital?
Why do we bother to learn about anything not digital in a digital media course?
What does digitizing mean?

50. Review Questions

51. Review Question
Digital data is _____ and analog information is _____. A. continuous; discrete B. discrete; continuous B

52. Review Question Digitization means converting _____ into _____.
analog information, digital data

53. Review Question
Converting from analog to digital involves a two-step process: _____ and _____.
sampling, quantization

54. Review Question
When analog information is converted to digital data, two properties affect the exactness of the digital representation, one from sampling and one from quantizing. Which of the following is a result of quantization? A. sampling rate B. bit depth B

55. Review Question
Which of the following refers to the number of allowable levels of digitized data? A. sampling rate B. bit depth B

56. Review Question
Which of the following can reduce file size of digital media? (More than one choice) A. decrease sampling rate B. increase sampling rate C. decrease bit depth D. increase big depth
A and C