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Basics of Video Courtesy of Professor Yao Wang Polytechnic University, Brooklyn, NY11201

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Presentation on theme: "Basics of Video Courtesy of Professor Yao Wang Polytechnic University, Brooklyn, NY11201"— Presentation transcript:

1 Basics of Video Courtesy of Professor Yao Wang Polytechnic University, Brooklyn, NY11201

2 Adapted from Yao Wang, 2004 Video Basics 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 –YCbCr format Video display –Spatial/temporal/bit-depth resolution

3 Adapted from Yao Wang, 2004 Video Basics3 Photometric Model of Video Capture Courtesy of Onur Guleryuz

4 Adapted from Yao Wang, 2004 Video Basics4 Geometric Model of Video Capture Camera center Image plane 2-D image 3-D point The image of an object is reversed from its 3-D position. The object appears smaller when it is farther away.

5 Adapted from Yao Wang, 2004 Video Basics5 Implication of Models in Analog World Miniature building Explosion from The Mummy Lighting in Filmmaking

6 Adapted from Yao Wang, 2004 Video Basics6 Progressive and Interlaced Raster Scans Field 1Field 2 Progressive Frame Interlaced Frame Interlaced scan is developed to provide a trade-off between temporal and vertical resolution, for a given, fixed data rate (number of line/sec). Horizontal retrace Vertical retrace

7 Adapted from Yao Wang, 2004 Video Basics7 Color TV Broadcasting and Receiving

8 Adapted from Yao Wang, 2004 Video Basics8 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

9 Adapted from Yao Wang, 2004 Video Basics9 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

10 Color ImageY image I image (orange-cyan)Q image (green-purple)

11 Adapted from Yao Wang, 2004 Video Basics11 I and Q on the color circle I: orange-cyan Q: green-purple

12 Adapted from Yao Wang, 2004 Video Basics12 Conversion between RGB and YIQ Y = R G B I = R G B Q = R G B R =1.0 Y I Q, G = 1.0 Y I Q, B =1.0 Y I Q. RGB -> YIQ YIQ -> RGB

13 Adapted from Yao Wang, 2004 Video Basics13 YUV in PAL

14 Adapted from Yao Wang, 2004 Video Basics14 YUV/RGB Conversion Y = (( ( 66 * R * G + 25 * B + 128) >> 8) + 16) U = ( ( -38 * R - 74 * G * B + 128) >> 8) V = ( ( 112 * R - 94 * G - 18 * B + 128) >> 8) Numerical approximations

15 Adapted from Yao Wang, 2004 Video Basics15 YIQ/YUV Comparison

16 Adapted from Yao Wang, 2004 Video Basics16 Different Color TV Systems

17 Adapted from Yao Wang, 2004 Video Basics17 Who uses what? From

18 Adapted from Yao Wang, 2004 Video Basics18 Digital Video Taken from EE465: Image Acquisition SamplingQuantization

19 Adapted from Yao Wang, 2004 Video Basics19 BT.601* Video Format * BT.601 is formerly known as CCIR601

20 Adapted from Yao Wang, 2004 Video Basics20 RGB YCbCr Analog video Digital video

21 Adapted from Yao Wang, 2004 Video Basics21 YUV vs. YCbCr

22 Adapted from Yao Wang, 2004 Video Basics22 Chrominance Subsampling Formats

23 Adapted from Yao Wang, 2004 Video Basics23 Digital Video Formats

24 Adapted from Yao Wang, 2004 Video Basics24 4:2:0 YUV Video Y: 288-by-352 U: 144-by-176V: 144-by-176

25 Adapted from Yao Wang, 2004 Video Basics25 Tricky Photometric Situations Shadow causes problem to background extraction Video enhancement

26 Adapted from Yao Wang, 2004 Video Basics26 Geometric Invariance

27 Adapted from Yao Wang, 2004 Video Basics27 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

28 Adapted from Yao Wang, 2004 Video Basics28 Resolution, Resolution, Resolution spatial temporal Bit-depth 1M10M 30fps 300fps 8bpp 32bpp

29 Adapted from Yao Wang, 2004 Video Basics29 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

30 Adapted from Yao Wang, 2004 Video Basics30 HDR Display (after Toner Mapping) Note that any commercial display devices we see these days are NOT HDR


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