Basics of Video Coding and H.263 Video Coding 김성재 Sep. 6, 2000

Basics of Video Coding and H.263 Video Coding 2 Content Basics of Video Coding –Introduction –Color Coordinate and Picture Format –Transform Coding - DCT –Quantization –Entropy Coding H.263 Video Coding –Introduction –Encoder Block Diagram –Overall Process –Motion Estimation –Quantization –VLC encoding of quantized transform coefficient

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 3 Introduction (1/4) Image Coding (Video Coding) –To represent an image(video) with as few bits as possible while preserving the level of distortion (quality) Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 4 Introduction (2/4) Typical Image Coding System Three Components in Image Coder Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 5 Introduction (3/4) Classification of Image Coding Techniques Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 6 Introduction (4/4) Features of Video Compression Algorithm –Random Access –Fast Forward/Reverse Searches –Reverse Playback –Audio-Visual Synchronization –Robustness to Errors –Coding/Decoding Delay –Format Flexibility Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 7 Color Coordinate and Picture Format (1/3) Human Visual System –Cone : near to fovea, for day vision, 7 million –Rod : away from fovea, for night vision, 120 million Color Coordinate –RGB –YUV –YC r C b Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 8 Color Coordinate and Picture Format (2/3) Picture Format Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 9 Color Coordinate and Picture Format (3/3) Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 10 DCT(Discrete Cosine Transform) (1/2) N 개의 입력 신호 에 대해서 1-D forward DCT 는 다음과 같이 정의 Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 11 DCT(Discrete Cosine Transform) (2/2) 4x4 2-D DCT Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 12 Scalar Quantization Basics of Video Coding 0 n bits/pixel Q r bits/pixel Original imageReconstructed image

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 13 Vector Quantization Basics of Video Coding Original image Reconstructed image Codebook

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 14 Huffman Coding Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 15 Arithmetic Coding Green-Green-Red Basics of Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 16 Introduction (1/2) Two basic compression algorithm –Block-based motion estimation/compensation : Reduction of the temporal redundancy –Transform domain(DCT)-based compression : Reduction of the spatial redundancy 3 types of pictures –I(Intra picture), P(Predicted picture), B(Interpolated picture) H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 17 Introduction (2/2) Structure of Video Data –Macroblock ¤Four Luminance(Y) Block ¤Two Chrominence(C r, C b ) Block –Block : 8x8 pixel H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 18 Encoder Block Diagram (1/2) H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 19 Encoder Block Diagram (2/2) oME1 Integer pixel motion estimation and INTRA/INTER decision oME2 Half pixel motion estimation oM1 Input frame store oM2 Decoded frame store oPRED Make prediction block oMBTYPE Decide block type and block pattern oVLC(C) VLC coding of transform coefficients oVLC(M) VLC coding of motion vectors oCC Coding control oDCT Discrete Cosine Transform oQ Quantizer H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 20 Overall Process (1/2)

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 21 Overall Process (2/2)

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 22 Motion Estimation (1/4) Integer pixel motion estimation – 움직임 탐색은 Y 에 대해 정수 화소 단위로 이루어진다. – 현재 입력 Block 과 이전 Frame 의 영상과 Macroblock 단위로 비교하여 SAD(Sum of Absolute Difference) 가 가장 작은 위 치를 찾는다. –Full search 가 사용되며 탐색범위는 현재 Macroblock 의 위치 에서 수평, 수직방향으로 화소가 된다 H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 23 Motion Estimation (2/4) INTRA/INTER Mode Decision –Integer pixel motion estimation 을 한 후에 Coder 는 INTRA 로 부호화할 것인지 INTER 로 부호화 할 것인지를 결정한다. –A < (SAD - 500) 이면 INTRA 모드로 선택된다. –INTER 모드가 선택되면 계속해서 Half pixel search 가 이루어 진다. H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 24 Motion Estimation (3/4) Half pixel search – 이전에 재생된 영상을 이용 – 탐색 범위는 정수단위의 움직임 벡터 위치에서 Half pixel 이 된다. –SAD(0,0) 는 100 을 뺀 값과 비교 C B D c A b d a Half pixel position Integer pixel position a = A b = (A+B)//2 c = (A+C)//2 d = (A+B+C+D)//4 // : Integer division with rounding to nearest integer H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 25 Motion Estimation (4/4) Differential coding of motion vectors –Motion vector 의 전송은 이전 Macroblock 의 Motion vector 와 의 차이를 전송 –Motion vector difference : MV2MV3 MVMV1 MV2MV3 MV(0, 0) MV1 MVMV1 MV2(0, 0) MVMV1 : Picture or GOB border MV : Current motion vector MV1 : Previous motion vector MV2 : Above motion vector MV3 : Above right motion vector H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 26 Quantization (1/2) · Notation - QP(Quantization Parameter) : 1~32 사이의 정수값 - Quantization step size : 2xQP - COF : 양자화 될 DCT 영역의 계수값 - LEVEL : COF 를 양자화한 절대값 - COF’ : 재생된 DCT 영역의 계수값 · Quantization –For INTRA : –For INTER : H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 27 Quantization (2/2) Dequantization Quantization for INTRA DC coefficient –8 bit 가 사용 –Quantization : –Dequantization : H.263 Video Coding

Sep. 6, 2000 Basics of Video Coding and H.263 Video Coding 28 VLC encoding of quantized transform coefficient Event 는 3 개의 Parameter 의 조합으로 이루어진다. (LAST, RUN, LEVEL) –LAST ¤0 : Not last coefficient ¤1 : Last nonzero coefficient –RUN : Number of zero coefficients preceding the current nonzero coefficient –LEVEL : Magnitude of the coefficient H.263 Video Coding