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Basics of Video

Video Processing & Communications. Basics of Video. Courtesy of Professor Yao Wang Polytechnic University, Brooklyn, NY11201 yao@vision.poly.edu. Outline. Video capture Photometric model Geometric model Analog video Progressive vs. interlaced rasters in analog TV system

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Basics of Video

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  1. Video Processing & Communications Basics of Video Courtesy of Professor Yao Wang Polytechnic University, Brooklyn, NY11201 yao@vision.poly.edu

  2. Outline • Video capture • Photometric model • Geometric model • Analog video • Progressive vs. interlaced rasters in analog TV system • Different color representations: YUV/YIQ • Digital video • Sampling/quantization • Y’CbCr format • Video display • Spatial/temporal/bit-depth resolution Video Basics

  3. Photometric Model of Video Capture Courtesy of Onur Guleryuz Video Basics

  4. Geometric Model of Video Capture 3-D point Camera center The image of an object is reversed from its 3-D position. The object appears smaller when it is farther away. 2-D image Image plane Video Basics

  5. Implication of Models in Analog World Miniature building Explosion from The Mummy Lighting in Filmmaking Video Basics

  6. Interlaced Frame Progressive Frame Field 1 Field 2 Progressive and Interlaced Raster Scans Horizontal retrace Vertical retrace Interlaced scan is developed to provide a trade-off between temporal and vertical resolution, for a given, fixed data rate (number of line/sec). Video Basics

  7. Color TV Broadcasting and Receiving Video Basics

  8. Why not using RGB directly? • R,G,B components are correlated • Transmitting R,G,B components separately is redundant • More efficient use of bandwidth is desired • RGB->YC1C2 transformation • Decorrelating: Y,C1,C2 are uncorrelated • C1 and C2 require lower bandwidth • Y (luminance) component can be received by B/W TV sets Color transformation is a compromised solution, but the ultimate one Video Basics

  9. YIQ in NTSC I (in-phase): orange-to-cyan Q (quadrature): green-to-purple (human eye is less sensitive) Q can be further bandlimited than I Phase=Arctan(Q/I) = hue, Magnitude=sqrt (I^2+Q^2) = saturation Hue is better retained than saturation Recall: Quadrature amplitude modulation (QAM) in digital communication Video Basics

  10. Color Image Y image I image (orange-cyan) Q image (green-purple)

  11. I and Q on the color circle Q: green-purple I: orange-cyan Video Basics

  12. Conversion between RGB and YIQ • RGB -> YIQ Y = 0.299 R + 0.587 G + 0.114 B I = 0.596 R -0.275 G -0.321 B Q = 0.212 R -0.523 G + 0.311 B • YIQ -> RGB • R =1.0 Y + 0.956 I + 0.620 Q, • G = 1.0 Y - 0.272 I -0.647 Q, • B =1.0 Y -1.108 I + 1.700 Q. Video Basics

  13. YUV in PAL Video Basics

  14. YUV/RGB Conversion Numerical approximations • Y = (( ( 66 * R + 129 * G + 25 * B + 128) >> 8) + 16) • U = ( ( -38 * R - 74 * G + 112 * B + 128) >> 8) + 128 • V = ( ( 112 * R - 94 * G - 18 * B + 128) >> 8) + 128 Video Basics

  15. YIQ/YUV Comparison Video Basics

  16. Different Color TV Systems Video Basics

  17. Who uses what? From http://www.stjarnhimlen.se/tv/tv.html#worldwide_0 Video Basics

  18. Digital Video Sampling Quantization Taken from EE465: Image Acquisition Video Basics

  19. BT.601* Video Format * BT.601 is formerly known as CCIR601 Video Basics

  20. RGB <--> Y’CbCr Analog video Digital video Video Basics

  21. YUV vs. Y’CbCr Video Basics

  22. Chrominance Subsampling Formats Video Basics

  23. Digital Video Formats Video Basics

  24. 4:2:0 YUV Video U: 144-by-176 V: 144-by-176 Y: 288-by-352 Video Basics

  25. Tricky Photometric Situations Shadow causes problem to background extraction Video enhancement Video Basics

  26. Geometric Invariance Video Basics

  27. Video Display • High-end • If the resolution of display device is higher than that of video sequence, what can we do? • Tradeoff between quality and complexity • Subjective evaluation of video quality • Low-end • If the resolution of display device is lower than that of video sequence, what can we do? • What if the bit-depth resolution is lower? (e.g., display video on PDAs and portable DVDs) It is the last and the least-researched component in visual communication systems Video Basics

  28. Resolution, Resolution, Resolution temporal 300fps 30fps 1M 10M spatial 8bpp 32bpp Bit-depth Video Basics

  29. High Dynamic Range Imaging Q: Can we generate a HDR image (16bpp) by a standard camera? A: Yes, adjust the exposure and fuse multiple LDR images together Video Basics

  30. HDR Display (after Toner Mapping) Note that any commercial display devices we see these days are NOT HDR Video Basics

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