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Understanding Uncompressed Video Size, Compression Ratios, and Sampling Theorems in Real-Time Systems

In this week’s class, we dive into critical concepts related to video processing in real-time systems. We will estimate rates for uncompressed video, calculate compression ratios, and explore the effects of aliasing, especially the stroboscopic effect. We'll discuss how images are stored in memory, focusing on pixel dimensions such as Full HD (1080p) and the implications of RGB channels. Additionally, we'll cover sampling errors, channel capacity, and the fundamentals of the Fourier Transform to enhance your understanding of data transmission and compression in digital media.

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Understanding Uncompressed Video Size, Compression Ratios, and Sampling Theorems in Real-Time Systems

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  1. SE-3910Real-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.

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

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

  4. How large is an uncompressed image? • 1080p • 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

  5. What is the uncompressed data-rate? • 1080p • 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

  6. 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

  7. 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

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

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

  10. Aliasing • http://photo.stackexchange.com/questions/24512/what-is-aliasing-and-anti-aliasing SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

  11. More aliasing • Single-Sensor Imaging: Methods and Applications for Digital Cameras, by RastislavLukac • http://www.openphotographyforums.com/forums/showthread.php?t=14988 SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

  12. 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

  13. Claude Shannon H – analog Bandwidth S – Signal power N – Noise power SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

  14. Signals as sums of sine-waves http://ccn.ucla.edu/BMCweb/SharedCode/slides/SlideFiles.html http://mathworld.wolfram.com/FourierSeriesSquareWave.html SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

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

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

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

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

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

  20. In-Class Exercise: If this is 1 second,what is the output if we sample 3 times per second? SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling

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

  22. 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

  23. 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

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