SE3910 Realtime Systems Week 7 Class 3 Announcement

SE-3910 Real-time Systems • Week 7, Class 3 – Announcement – Estimating rates • • Uncompressed Video Size Compression Ratio Frame rate – the Stroboscope effect (Aliasing) Channel capacity – Fourier Transform • Sampling error SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling, Some from Dr. Hornick, etc. 1

How is an image stored in memory? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 2

Full HD/1080 p SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 3

How large is an uncompressed image? • 1080 p – 1920 x 1080 – 3 channels (RGB), each 8 bits • How many bytes for one image? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 4

What is the uncompressed data-rate? • 1080 p – 1920 x 1080 – 3 channels (RGB), each 8 bits – 60 fps • What is the data rate, in Xbits per second? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 5

H. 262 Compression • H. 262 compression has a target maximum data rate of 25 Mb/s. Supposing this means Mebibits/s (or Megabits/s), what is the desire compression ratio? compression ratio = compressed / uncompressed SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 6

The Stroboscopic Effect • Have you ever noticed something that is in motion seem to stop? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 7

The Stroboscopic Effect (Aliasing) • http: //upload. wikimedia. org/wikipedia/comm ons/7/77/Propeller_strobe. ogv • http: //upload. wikimedia. org/wikipedia/comm ons/e/ef/The_wagon-wheel_effect. ogv SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 8

Safety • See, e. g. http: //www. seasshops. ucla. edu/services/stud SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 9

Aliasing • http: //photo. stackexchange. com/questions/2 4512/what-is-aliasing-and-anti-aliasing SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 10

More aliasing • Single-Sensor Imaging: Methods and Applications for Digital Cameras, by Rastislav SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 11

Transmitting data • Physical Layer – You didn’t talk too much about this in Network Protocols – Can occur through many mediums • • Twisted Pair Coaxial Cable Fiber Optics Wireless SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 12

Claude Shannon • SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 13

Signals as sums of sine-waves http: //ccn. ucla. edu/BMCweb/Shared. Co lides/Slide. Files. html http: //mathworld. wolfram. com/Fourier. Serie SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick s. Square. Wave. html Much Material: Dr. Schilling 14

What is analog bandwidth? Time Freq. http: //www. mathworks. com/matlabcentral/fileexchange/22214 -voice-audio. SE-3910 - Dr. Josiah Yoder processing Slide style: Dr. Hornick Much Material: Dr. Schilling 15

SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 16

Channel capacity • SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 17

In-class exercise • The old analog TV channels had a bandwidth of 6 MHz • Supposing a SNR of 50 d. B, what is the maximum possible bit-rate? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 18

Rates Wiring Type Bandwidth CAT 3 16 MHz CAT 5 100 MHz Coaxial Cable (50 Ohm) 1 -2 GHz Fiber Optic 50000 GHz SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 19

In-Class Exercise: If this is 1 second, what is the output if we sample 3 times per second? 1 0, 8 0, 6 0, 4 0, 2 0 0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 -0, 2 -0, 4 -0, 6 -0, 8 -1 SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 20

Sampling Theorem (again Nyquist) • fs = 2 B (B is bandwidth of signal) SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 21

Discretization • Consider an analog signal that will vary between two values – say 0 and VH volts • Discretization refers to the “levels” the ADC is able to resolve the analog signal to: – a 2 -bit converter can resolve 4 different discrete levels SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 22

Discretization Error • Difference between the actual analog value and quantized digital value due is called quantization error. – Due either to rounding or truncation. SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 23