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

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”?

Warm up Questions What is the biggest number I can get with 3 binary bits? 111 = 1 x 22 + 1 x 21 + 1 x 20 = 7 How few binary bits do I need to save the number “123”? 1, 2, 4, 8, 16, 32, 64, 128 - too big So 7 bits

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 72 101 108 108 111 33  number  binary

ASCII Table

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

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

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)

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?

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?

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

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

4 bit Gray Scale 16 numbers 16 different shades 1111 15 1110 14 1101 13 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

Gray scale 4 Bits 1 Bit each pixel 0 or 1 2 Bits 00 8 Bits 01 10 11 8 Bits Each pixel 00000000

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

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

More bits = More colours 8-bit Color 256 colors

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

Picture File Size Paint – default size is 512 x 385 pixels = 197120 pixels If each pixel holds 1 bit (black or white) 197120 pixels x 1 bit / pixel = 197120 bits 197120 / 8 = 24640 bytes What if each pixel holds 8 bit colour? 197120 pixels x 8 bits / pixel x 1 byte / 8 bits = 197120 bytes 24 bit colour? 591360 bytes! Lots of 1 & 0, bumps on a CD, load time!

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

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

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!! = 110400000 bits for a 1-second movie!!

Digitizing Videos 13.8 MB for a 1 second video

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

Homework Number Systems worksheet Notes – fill in

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