A Study of Digital Video Compression Technology

In this thesis, we studied the three methods of digital video encoder with either discrete cosine transform (DCT) or discrete wavelet transform (DWT), 2D method (DCT & DWT), 3D method (DCT & DWT) and hybrid method. The aim of the video compression is to achieve higher compression ratio with little elimination of visual quality and lower computational complexity. By exploiting the redundancies in the video sequence and the human visual response we could reduce storage of information in the video sequence and then apply the information theory (Huffman coding) which is a lossless coding method using by text compression tool such as Winzip or Winrar. 2D model with 2D-DCT is adopted by the JPEG for image compression. In application of video sequence, it is called motion JPEG. For preventing the block effects of the 2D-DCT method, DWT replaces DCT. The DWT is completed by two orthogonal or biorthogonal filter banks and then the DWT coefficients are transmitted by the SPIHT Algorithm. For exploiting the temporal redundancies, the 3D model of digital video compression is the direct method. By applying the 3D transform either with the 3D-DCT or 3D-DWT, we can transform the temporal redundancies to the frequency domain and then quantize the coefficients according to the human visual response. In the previous study, the energy of 3D-DCT coefficients is highly compacted in the hyperbolic plane, thus our mission is to quantize the coefficients outside the plane to zero for achieving higher compression ratio without lower visual quality. The quantization value could be obtained form the proposed equation. The zig-zag scan order of the 2D-DCT is not suitable for the 3D-DCT, because it can’t achieve higher compression by using variable length coding. The optimal scan order should be implemented according to the probability of non-zero coefficients. Hybrid method is also a method of eliminating the temporal redundancies of video sequence by motion estimation. It reduces the temporal redundancies by subtracting the predicted frame from the current frame, thus it is more suitable for the high motion video sequence but 3D method isn’t.CHAPTER 1 MOTIVATION 6 CHAPTER 2 VIDEO BASICS 8 2.1 HUMAN PERCEPTION OF COLOR 8 2.2 FREQUENCY RESPONSE OF THE HVS 9 2.2.1 Spatial Frequency 9 2.2.2 Angular Frequency 9 2.2.3 Temporal Frequency 10 2.2.4 Temporal Frequency Response 11 2.2.5 Spatial Frequency Response 12 2.2.6 Spatiotemporal Frequency Response 12 2.3 DIGITAL VIDEO FORMAT AND CHROMINANCE SUBSAMPLING 13 2.4 VIDEO QUALITY MEASUREMENT 15 CHAPTER 3 2D METHOD OF DIGITAL VIDEO COMPRESSION – 2D-DCT & 2DDWT 17 3.1 INTRODUCTION TO 2D-DCT DIGITAL VIDEO COMPRESSION 17 3.2 DISCRETE COSINE TRANSFORM 18 3.3 QUANTIZATION 21 3.4 ZIG-ZAG SCAN 23 3.5 RUN LENGTH CODING & VARIABLE LENGTH CODING 24 3.6 INTRODUCTION TO 2D-DWT DIGITAL VIDEO COMPRESSION 27 3.7 2 DIMENSIONAL DISCRETE WAVELET TRANSFORM 27 3.8 SET PARTITIONING IN HIERARCHICAL TREES 31 3.9 EXPERIMENTAL RESULTS 35 CHAPTER 4 3D METHOD OF DIGITAL VIDEO COMPRESSION – 3D DCT & 3D DWT 41 4.1 INTRODUCTION TO 3D-DCT DIGITAL VIDEO COMPRESSION 41 4.2 3 DIMENSIONAL DISCRETE COSINE TRANSFORM 42 4.3 OPTIMAL QUANTIZATION TABLE 43 4.4 SCAN ORDER OF 3D-DCT QUANTIZED COEFFICIENTS 46 4.5 INTRODUCTION TO 3D-DWT DIGITAL VIDEO COMPRESSION 48 4.6 3 DIMENSIONAL DISCRETE WAVELET TRANSFORM 49 4.7 QUANTIZATION 50 4.8 HUFFMAN CODING 52 4.9 EXPERIMENTAL RESULTS 53 CHAPTER 5 HYBRID METHOD OF DIGITAL VIDEO COMPRESSION - MPEG2 STANDARD 60 5.1 INTRODUCTION TO MPEG2 60 5.2 MOTION ESTIMATION – BLOCK MATCHING METHODS 61 5.3 SEARCH ALGORITHM 62 5.3.1 Full Search Algorithm 62 5.3.2 One At a Time Search Algorithm 63 5.3.3 Two-Dimensional Logarithmic Search Algorithm 63 5.3.4 3-Steps Search Algorithm 64 5.3.5 Cross-Search Algorithm 65 5.3.6 Diamond Search 65 5.3.7 Half pixel Refinement 66 5.4 MOTION PREDICTION & COMPENSATION 67 5.5 GROUP OF PICTURE & TRANSMISSION ORDER OF THE VIDEO FRAMES 68 5.6 MPEG2 VIDEO STRUCTURE AND VIDEO STREAM SYNTAX 71 5.6.1 Video Sequence Header 72 5.6.2 Group of Picture Header 73 5.6.3 Picture Header 73 5.6.4 Slice Header 74 5.6.5 Macro Block Header 75 5.6.6 Block Header 76 5.8 EXPERIMENTAL RESULTS 77 CHAPTER 6 SUMMARY AND FUTURE WORKS 81 REFERENCES 8