1. Agenda Last class: Memory, Digitizing Numbers Today: Digitizing: Text
Sound – skip
Pictures
Movies
Software Quiz

2. Warm up Questions
What is the biggest number I can get with 3 binary bits?
How few binary bits do I need to save the number “123”?

3. Warm up Questions
What is the biggest number I can get with 3 binary bits?
111 = 1 x x x 20 = 7
How few binary bits do I need to save the number “123”?
1, 2, 4, 8, 16, 32, 64, too big So 7 bits

4. Digitizing Text
When you send a text message, the letters abcd... ABCD.. <>,.;_+-*/[ ]” etc. are also changed into numbers.
ASCII Code (1968)
American Standard Code for Information Interchange Eg: 65 = A, 97 = a
H e l l o !  text  number
 binary

5. ASCII Table

6. Digitizing Pictures A picture is just a table of numbers
The screen is many small pixels
Each pixel has 1 number
Resolution: number of pixels
Black & White = 0 & 1 (1 bit) 1

7. Resolution Example 1
Small resolution (3x3)
6x6 1

8. Resolution Example More resolution = more pixels
Can draw smaller details
NOT size of picture!
Copy following diagram
Show binary for pix
Black = 0 White 1
How many bytes? (ignore red)

9. Resolution Example More resolution = more pixels
Can draw smaller details
NOT size of picture!
Copy following diagram
Show binary for pix
Black = 0 White 1
How many bytes?

10. Resolution Example More resolution = more pixels
Can draw smaller details
NOT size of picture!
Copy following diagram
Show binary for pix
Black = 0 White= 1
How many bytes?

11. Resolution Example More resolution = more pixels
Can draw smaller details
NOT size of picture!

12. Gray Scale 1 bit = 0 or 1 = black or white More bits = gray scale

13. 4 bit Gray Scale 16 numbers 16 different shades 1111 15 1110 14 110113
1100 12
1011 11
1010 10
1001 9
1000 8
0111 7
0110 6
0101 5
0100 4
0011 3
0010 2
0001 1
0000
4 bit Gray Scale
16 numbers
16 different shades

14. Gray scale 4 Bits 1 Bit each pixel 0 or 1 2 Bits 00 8 Bits01 10 11
8 Bits
Each pixel

15. Digitizing Colour Each pixel has a Red Green Blue number Example:
A red pixel has 100
A white pixel has 111
Example: The red circle with blue inside using 6x6 pixel resolution R G B 1
111
100
001

16. Digitizing Colour 3-bit colour = 8 colours 111 110 101 100 011 010 001
000

17. More bits = More colours
8-bit Color 256 colors

18. 3, 6, 9, 12, 15, 18, 24 bit RGB

20. Picture File Size
Paint – default size is 512 x 385 pixels = pixels
If each pixel holds 1 bit (black or white)
pixels x 1 bit / pixel = bits / 8 = bytes
What if each pixel holds 8 bit colour?
pixels x 8 bits / pixel x 1 byte / 8 bits = bytes
24 bit colour? bytes! Lots of 1 & 0, bumps on a CD, load time!

21. Digitizing Pictures Summary
Applications:
Computer screen, TV screen
Cell phone, iPod screen
Digital Camera

22. Digitizing Videos A video is just many pictures
Like a cartoon animation or flip book
Quality depends on frame rate
Frames per second (FPS)
Higher FPS = smoother
Movie: 24 FPS
TV: 30 FPS

35. Digitizing Videos
So if your iPhone records at 30 FPS at 640 x 480 resolution, you are saving
30 pictures per second
Each picture has 640 x 480 pixels
Each pixel has 12 bit RGB colour
12 x 640 x 480 / 8 = 460,800 bytes almost 0.5 MB for ONE frame of video!
0.5 MB x 30 frames / second x 1 s video? = 13.8 MB for a 1-second video!! = bits for a 1-second movie!!

36. Digitizing Videos
13.8 MB for a 1 second video

37. Digitizing Videos Research & Careers:
How to make the file size smaller?
Reduce FPS?
Reduce pixel resolution?
Reduce colour resolution?
Compress information – do you need ALL of it?
Make smaller computer chips that can store more MB or GB of memory

38. Homework
Number Systems worksheet
Notes – fill in

39. Digitizing Sounds / Voice
When you talk, you make sound waves like this:
To turn it into numbers, you must pick some points = SAMPLING (done by microphone)
Eg: every 0.5 s, or 2 Hz
The more frequently you sample, the higher the quality
Too slow? Wrong signal.
Some high frequency information will be lost. Your voice sounds different.
Too much? Takes more memory / bytes to store it