1. Data Compression

2. How Is This Possible? Entire King James Bible : 4,834,757 bytes
Zip Archive Containing It: 1,339,843 bytes

3. More Questions
Why does this file:
Compress different than:

4. Behind The Scenes Compression used for: ~50% of web traffic
Most audio/video files
Sometimes for every file on a drive

5. Trick 1:
Describe the contents of this file in as few words as possible…

6. Trick 1: Run Length Encoding :
Describe repetition as: (How many times)What to repeat A

7. RLE Examples ABABABABABAB 6AB AAABBBBBAAACC 3A,5B,3A,2C
(5)1,(1)0,(6)01

8. RLE Fail This file doesn't just have A's:
80A,1newline,80A,1newline,80A,1newline…

9. Trick 2 Same As Earlier: ABCDEFG-b7c7
Describe patterns with instructions to go back x and copy y characters
ABCDEFG-b7c7
"Write down ABCDEFG, then go back 7 characters and copy the next 7 characters to the end of what you have"

10. Same As Earlier
ABCDEFG-b7c7

11. Same As Earlier
ABCDEFG-b7c7 ABCDEFG

12. Same As Earlier
ABCDEFG-b7c7 ABCDEFG

13. Same As Earlier
ABCDEFG-b7c7 ABCDEFGA

14. Same As Earlier
ABCDEFG-b7c7 ABCDEFGAB

15. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABC

16. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABCD

17. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABCDE

18. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABCDEF

19. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABCDEFG

20. Same As Earlier
ABCDEFG-b7c7 ABCDEFGABCDEFG

21. Same As Earlier
AB-b2c6

22. Same As Earlier
AB-b2c6 AB

23. Same As Earlier
AB-b2c6 AB

24. Same As Earlier
AB-b2c6 ABA

25. Same As Earlier
AB-b2c6 ABAB

26. Same As Earlier
AB-b2c6 ABABA

27. Same As Earlier
AB-b2c6 ABABAB

28. Same As Earlier
AB-b2c6 ABABABA

29. Same As Earlier
AB-b2c6 ABABABAB

30. Same As Earlier
AB-b2c6 ABABABAB

31. Same As Earlier
AB-b2c2-C-b3c4

32. Same As Earlier
AB-b2c2-C-b2c5 AB

33. Same As Earlier
AB-b2c2-C-b2c5 AB

34. Same As Earlier
AB-b2c2-C-b2c5 ABAB

35. Same As Earlier
AB-b2c2-C-b2c5 ABAB

36. Same As Earlier
AB-b2c2-C-b2c5 ABABC

37. Same As Earlier
AB-b2c2-C-b2c5 ABABC

38. Same As Earlier
AB-b2c2-C-b2c5 ABABCB

39. Same As Earlier
AB-b2c2-C-b2c5 ABABCBC

40. Same As Earlier
AB-b2c2-C-b2c5 ABABCBCB

41. Same As Earlier
AB-b2c2-C-b2c5 ABABCBCBC

42. Same As Earlier
AB-b2c2-C-b2c5 ABABCBCBCB

43. Same As Earlier
AB-b2c2-C-b2c5 ABABCBCBCB

44. Shorter Symbol Trick Shorter Symbol Trick:
Use minimum number of bits to represent different symbols in message
More common symbols get shorter representation

45. More Common But A is more common: AAAABAAC
So maybe we can use a shorter code for it 
(10 bits)

46. Why Does it Work No code is a prefix for another 010110010 ABCAAB
0 : it is an A
1 : keep going
ABCAAB

47. Why Does it Work A BAD code  010 010 AB DA
0 : is it an A? is it the start of a D?
AB DA

48. Building a Code
CS160 Reader…
Huffman Code Building

49. Lossy Compression Lossless compression :
Can recreate original perfectly
Algorithms: Run length encoding, same as earlier, shorter symbol
Examples: zip files, www traffic

50. Lossy Compression Lossy compression
Original can NOT be recreated perfectly

51. My Kids Kb

52. Every Other Line/Column Removed

53. Remaining pixels packed back down : 320Kb

54. Blown back up vs original
Original Compressed

55. Only keep every 4th line/column : 81 Kb

56. Real JPEG
Image broken into blocks of pixels

57. Real JPEG
Each block processed seperately

58. Real JPEG
Block processed, to look for compressible patterns

59. Real JPEG
Patterns can more or less recreate image

60. JPEG 200%
No compress Low compress Med compress High compress