Video Concepts and Techniques 1 SAMARTH COLLEGE OF ENGINEERING &TECHNOLOLOGY DEPARTMENT OF ELECTRONIC & COMMUNICATION ENGINEERING 5th semester (E&C) Subject Code [ ] Guided By:- Prof. NISHIDH PATEL Prepared By:- 1.PATEL MAYURKUMAR D. ( ) 2.CHAUHAN HARDIKSINH R. ( ) 3. PATEL SRUSHTI P. ( ) 4. ACHARYA SUNITA S. ( )

2 Outline Fundamental Concepts Basic Video Compression Techniques MPEG Video Coding I – MPEG-1 and 2 MPEG Video Coding II – MPEG-4, 7, and Beyond

3 Types of Video Signals  3 types: Component Video, Composite Video, S-Video  Component Video – 3 signal use 3 separate video signals for red, green, and blue image planes. most computer systems use it. get best color reproduction since no crosstalk between channels. however, requires more bandwidth and good synchronization.  Composite Video - 1 signal chrominance and luminance signals are mixed into a single carrier. chrominance is composition of (I and Q, or U and V) a color subcarrier put chrominance at high-frequency end of the signal shared with luminance signal. some interference between luminance and chrominance signals.  S-Video - 2 Signals uses two wires for luminance and composite chrominance signals. less crosstalk between them.

4 Analog Video  Interlaced scanning odd-numbered lines traced first, then even-numbered lines traced horizontal retrace: the jump from Q to R, during which the electronic beam in CRT is blanked. vertical retrace: the jump from T to U or V to P.  NTSC (National Television System Committee) TV standard used in North America and Japan. 4:3 aspect ratio (ratio of picture width to height) 525 scan lines per frame at 30 frames per second (fps).

5 Digital Video  Advantages: stored in memory, ready to be processed (noise removal, cut and paste), and integrated to various multimedia applications repeated recording does not degrade image quality ease of encryption and better tolerance to channel noise  Chroma Subsampling human see color with much less spatial resolution than black/white how many pixel values should be actually sent? scheme (4:4:4): no chroma subsampling is used: each pixel's Y, Cb and Cr values are sent. scheme (4:2:2): horizontal subsampling of Cb, Cr signals by a factor of 2. all Ys are sent, and every two Cb's and Cr's are sent. scheme (4:1:1): subsamples horizontally by a factor of 4 scheme (4:2:0): subsamples in both the horizontal and vertical dimensions by a factor of 2. (used in JPEG and MPEG)

6 Video Compression  A video consists of a time-ordered sequence of frames, i.e.,images.  Video Compression (Static) predictive coding based on previous frames. temporal redundancy: consecutive frames in a video are similar subtract images in time order, and code the residual error.  The approach of deriving the difference image (subtract image from the other) is ineffective because of object motion.  Steps of Video compression based on Motion Compensation (MC) 1. Motion Estimation (motion vector search). 2. MC-based Prediction. 3. Derivation of the prediction error, i.e., the difference.

7 Motion Compensation  For efficiency, each image is divided into macroblocks of size N X N.  The current image frame is referred to as Target Frame.  A match is sought between the macroblock in the Target Frame and the most similar macroblock in previous and/or future frame(s) (referred to as Reference frame(s)).  motion vector MV: the displacement of the reference macroblock to the target macroblock.  Prediction error: the difference of two corresponding macroblocks.

8 Video Coding Evolution