videoBasicsl

Avinash Sawant 01-Feb-09 : 

Avinash Sawant 01-Feb-09

Image : 

Image

Pixel Arrays : 

Pixel Arrays QSIF (19Kp) SIF (82Kp) 601 (300Kp) SVGA (500Kp) ATV (1Mp) Workstation (1Mp) HDTV (2Mp) 120 240 483 600 720 900 1080 160 352 720 800 1152 1280 1920

Image and Video : 

Image and Video

Formats : 

Formats RGB is not used for transmission of signals between capture and display devices b Too expensive, needs too much bandwidth .n capture and l Converted to luminance and chrominance formats Use standard YIQ or YUV format

Why Compression? : 

Why Compression? Multimedia applications generates a lot of data Need to compress data for efficient storage Need to compress data for efficient transmission.

Sequential JPEG Encoder and Decoder : 

Sequential JPEG Encoder and Decoder Forward Discrete Cosine Transform Quantizer Entropy Encoder Table Specification Table Specification Entropy Decoder Dequantizer Inverse DCT Table Specification Table Specification Source Image Data Reconstructed Image Data Compressed Image Data Compressed Image Data 8x8 blocks

Slide 8: 

DCT example

Slide 9: 

DC and AC coefficient DC Coefficient : First coefficient in every 8 x 8 block Represents the average value of pixels in block AC Coefficients : Remaining 63 coefficients in every 8 x 8 block DC Coefficients: treated separately from the AC Coefficients Differential values of DC coeffs. of all blocks are derived and encoded

Entropy Coding : 

Entropy Coding Assigns fewer bits to symbols that appear more often and more bits to the symbols that appear less often Efficient when occurrence probabilities vary widely Huffman codebook from the set of symbols and their occurring probabilities Two properties: generate compact codes prefix property Run-length Coding

How to achieve Compression ? : 

How to achieve Compression ? Redundancies in Video Statistical Spatial ( Intra Frame) Psychovisual Temporal ( Inter Frame) Luminance / Chrominance Frequency

Spatial Redundancy : 

Spatial Redundancy Take advantage of similarity among most neighboring pixels

Spatial Redundancy Reduction : 

Spatial Redundancy Reduction RGB to YUV less information required, same visually Macro Blocks Take groups of pixels DCT Represent pixels in blocks with fewer numbers Quantization Reduce data required for co-efficients Entropy coding Compress

Temporal redundancy : 

Temporal redundancy Next frame

Temporal Redundancy Reduction : 

Temporal Redundancy Reduction

Frame structure : 

Frame structure

I-frame coding : 

I-frame coding

P-frame coding : 

P-frame coding

Slide 20: 

Finding Best Matching Block

Slide 21: 

Finding Motion Vector

Video Stream Data Structure : 

Video Stream Data Structure

Video Encoder : 

Video Encoder

Video Decoder : 

Video Decoder

Slide 25: 

Thank You