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Stanford EE 368 - Image and Video coding Standards

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1Bernd Girod: EE368b Image and Video Compression Coding Standards no. 1Overview:image and video coding standardsn JPEGn MPEG-1 and MPEG-2n H.261 and H.263n Progress in video compressionBernd Girod: EE368b Image and Video Compression Coding Standards no. 2JPEG: backgroundn JPEG = Joint Photographic Experts Group: Joint standards committee of ITU-T and ISOn Flexible standard for monochrome and color image compression: “Digital Compression and Coding of Continuous-tone Still Images”n Intraframe coding scheme, optimized for still imagesn Flexible picture sizen Coding of color components separately, arbitrary color spaces possible, best compression for Y/R-Y/B-Yn Variable compression ration Compression 24:1 for ITU-R 601 images without loss of quality2Bernd Girod: EE368b Image and Video Compression Coding Standards no. 3JPEG derived industry standardsn JFIF (JPEG File Interchange Format, <xxxx.jpg>)n JTIP (JPEG Tiled, Pyramid Format)n TIFF (Tagged Image File Format)n SPIFF (Still Picture Interchange File Format, JPEG Part 3)n FlashPixl Developed by Kodak, Hewlett- Packard, Microsoft (1996)l Widely used in digital still camerasBernd Girod: EE368b Image and Video Compression Coding Standards no. 4JPEG: baseline algorithmBlockwise 8x8 DCTweighting / uniform quantizationHuffman CodingBlockwise inverse 8x8 DCTInverse weightingHuffman DecodingImage inImage out3Bernd Girod: EE368b Image and Video Compression Coding Standards no. 5JPEG: quantizer stepsizen Different weighting matrices are standardized, adapted to human visual contrast sensitivityn Example: Inverse weighting for ITU-R 601 images16 11 10 16 24 40 51 6112 12 14 19 26 58 60 5514 13 16 24 40 57 69 5614 17 22 29 51 87 80 6218 22 37 56 68 109 103 7724 35 55 64 81 104 113 9249 64 78 87 103 121 120 10172 92 95 98 112 100 103 9917 18 24 47 99 99 99 9918 21 26 66 99 99 99 9924 26 56 99 99 99 99 9947 66 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 99Luminance ChrominanceBernd Girod: EE368b Image and Video Compression Coding Standards no. 6JPEG: coding of DCT coefficientsn Differential coding of DC coefficient (0,0)n Zig-zag-scan and run-level-coding of AC coefficientsn Two options for Huffman coding:l with predefined code tables (one-pass system)l code tables optimized for individual image (two-pass system)4Bernd Girod: EE368b Image and Video Compression Coding Standards no. 7JPEG-2000 n New generation JPEG standard, recently finalized.n Discrete wavelet transformn Embedded scalar quantization with deadzonen Entropy-coding: bit-plane arithmetic coding with „context modeling“n Typically 30% lower bit-rate than old JPEG at the same image qualityBernd Girod: EE368b Image and Video Compression Coding Standards no. 8Video coding standards2-6 Mbps64 kbps< 28.8 kbpsMPEG-2H.261H.263 digital TV ISDN picture phonePSTN picture phone ITU-R 601 166 Mbit/s5Bernd Girod: EE368b Image and Video Compression Coding Standards no. 9Generic encoder block diagram for H.261, H.263, and MPEGIntraframeDCT coderIntraframe Decoder-DecoderVideo signalSChannel ControleMotioncompensatedpredictorBernd Girod: EE368b Image and Video Compression Coding Standards no. 10Image formatsITU-R 601sub QCIFQCIFCIF352 x 288176 x 1446Bernd Girod: EE368b Image and Video Compression Coding Standards no. 11ISO MPEGn MPEG-1 Standard (1991)l Target bit-rate about 1.5 Mbit/s l Typical image format CIF, no interlacel Frame rate 24 ... 30 fpsl Main application: video storage for multimedia (e.g., on CD-ROM)n MPEG-2 Standard (1994)l Extension for interlace, optimized for TV resolution (NTSC: 704 x 480 Pixel)l Image quality similar to NTSC, PAL, SECAM at 4 - 8 Mbit/sl HDTV at 20 Mbit/sBernd Girod: EE368b Image and Video Compression Coding Standards no. 12MPEG: hierarchical syntax In "Video Sequence"n "Group of Pictures" = “GOP“, GOP structure is very flexibleI-PictureP-PictureP-PictureB-Picturestime7Bernd Girod: EE368b Image and Video Compression Coding Standards no. 13MPEG: hierarchical syntax IIn "Picture": N x M luminance samples, N/2 x M/2 Cb- and Cr-samplesn "Slice": Sequence of Macroblocksn "Macroblock”n "Block": 8x8 samples16x16 luminancesamples 0 12 34 58x8 Cb-samples8x8 Cr-samplesBernd Girod: EE368b Image and Video Compression Coding Standards no. 14MPEG: coding of I-picturesn I-pictures: intraframe codedn 8x8 DCTn Arbitrary weighting matrix for coefficientsn Differential coding of DC-coefficientsn Uniform quantizationn Zig-zag-scan, run-level-codingn Entropy codingn Unfortunately, not quite JPEG8Bernd Girod: EE368b Image and Video Compression Coding Standards no. 15MPEG: coding of P-picturesn Motion-compensated prediction from an encoded I-picture or P-picture (DPCM)n Half-pel accuracy of motion compensation, bilinear interpolationn One displacement vector per macroblockn Differential coding of displacement vectorsn Coding of prediction error with 8x8-DCT, uniform thresholdquantization, zig-zag-scan as in I-picturesBernd Girod: EE368b Image and Video Compression Coding Standards no. 16MPEG: coding of B-picturesn Motion-compensated prediction from two consecutive P- or I-picturesl either• only forward prediction (1 vector/macroblock)l or• only backward prediction (1 vector/macroblock)l or• Average of forward and backward prediction = interpolation (2 vectors/macroblock)n Half-pel accuracy of motion compensation, bilinear interpolationn Coding of prediction error with 8x8-DCT, uniformquantization, zig-zag-scan as in I-pictures9Bernd Girod: EE368b Image and Video Compression Coding Standards no. 17ITU-T Rec. H.261n International standard for ISDN picture phones and for video conferencing systems (1990)n Image format: CIF (352 x 288 Y samples) or QCIF (176 * 144 Y samples), frame rate 7.5 ... 30 fpsn Bit-rate: multiple of 64 kbps (= ISDN-channel), typically 128 kbps including audio.n Picture quality: for 128 kbps acceptable with limited motion in the scenen Stand-alone videoconferencing system or desk-top videoconferencing system, integrated with PCBernd Girod: EE368b Image and Video Compression Coding Standards no. 18ITU-T Rec. H.263n International standard for picture phones over analog subscriber lines (1995)n Image format usually CIF, QCIF or Sub-QCIF, frame rate usually below 10


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