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Object Based Video Coding - A Multimedia Communication Perspective

Object Based Video Coding - A Multimedia Communication Perspective. Muhammad Hassan Khan 2004-03-0020. Overview. Motivation for Video Coding Today’s Video Coding Problems with today’s video coding Desirable Features Solution to get desirable features Object Based Video Coding

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Object Based Video Coding - A Multimedia Communication Perspective

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  1. Object Based Video Coding - A Multimedia Communication Perspective Muhammad Hassan Khan 2004-03-0020

  2. Overview • Motivation for Video Coding • Today’s Video Coding • Problems with today’s video coding • Desirable Features • Solution to get desirable features • Object Based Video Coding • MPEG-4 Support • Model Based Coding • Major Problem: Segmentation • Segmentation by Graph Cuts • Architecture to Incorporate this segmentation mechanism with MPEG-4 bit stream

  3. Why Video Coding? • Consider a 1 minute video with 60fps • No of frames = 60 x 60 = 3600 • Given that each color frame in the video was a 640 x 480 pixels • The size of the raw video comes out to be? • 3600 x 640 x 480 x 3 = 3,317,760,000 bits • Of the order of Gbs • Now a days one might say that memory is no big deal… BUT • What if we want to transfer this file from one node to the other node over a network! • Things would collapse very soon • Just imagine if the video was 1 hour duration rather than 1 minute!!! • I hope the need for video coding is now obvious 

  4. Today’s Video Coding • Designed for natural scenes • Higher frequency DCT coefficients are quantized • Sharp edges are not well preserved YUV (lossy) Motion DCT Quantize (lossy) Order Entropy

  5. Problems with Today’s Video Coding • Poor performance in case of • Anything with sharp edges • Highly textured regions • Texts (Channel Logos) • The bit stream produced by today’s coders is also debatable in that weather it is the MOST optimal bit stream • In fact what is a most optimal bit stream is still a question

  6. Desired Features • Better compression • Improved quality • Interactivity and Manipulation of Content • Error Resilience • Processing of content in the compressed domain • Identification and selective coding/decoding of the object of interest • Facilitate Search / Indexing (MPEG-7)

  7. Solution to Get Desirable Features • MPEG-4 • Support for Object Based Coding • Rather than conventional block based coding for natural images • The scene should be divided hierarchically into objects • The scene will now be described by the objects placed in a hierarchical manner • A sample is presented in the next slide

  8. The scene divided into objects Hierarchical Description

  9. The decoding process

  10. Meshed Video • 2D mesh tessellates the video into patches • Motion vector for each vertex • Motivation • Modeling (Motion and Shape)

  11. Problems with Mesh Based Coding • Works fine with previously known models and caters for a small class of objects • The reliable tracking of features or control points along the video • E.g. FAPs • A ready-made model is assumed, 2D or 3D model of the object has to be known • A more general approach was required • Object Based Video Coding • Shape, Color, and Motion

  12. Requires a Major Step! • Segmentation • Dividing the scene into objects • In simplest form these objects can be foreground and background • In more complex situations there can be multiple objects in the scene • Segmentation is required to extract the objects • Computing Motion • Object Based Motion • Parameterized Motion Information

  13. Segmentation by Graph Cuts • Uses Max-Flow Min-Cut Algorithm from Graph Theory • Divides the data into regions based on an energy function, usually employed to the intensities of the image • A smoothness function is also used to make sure that the segmentation achieved is consistent • Details will be provided in the final presentation

  14. Architecture • We will also propose mechanism to assign motion information to the segmented objects • Our approach will be as consistent as possible with the support provided by MPEG

  15. References • Gary J. Sullivan, Pankaj Topiwala, Ajay Luthra SPIE Conference on Applications of Digital Image Processing XXVII, Special Session on Advances in the New Emerging Standard: H.264/AVC, August, 2004 • Gabriel Antunes, Abrantes, Fernando Pereira, MPEG-4 Facial Animation Technology : Survey, Implementation and Results, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 9, No. 2, March 1999 • Roger H Clarke, Image and Video Compression: A Survey Department of Computing and Electrical Engineering, Heriot-Watt University, Riccarton, Edinburgh EH14 4 AS, Scotland. • Noel Brady, MPEG-4 Standardized Methods for the Compression of Arbitrarily Shaped Video Objects, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 9, No. 8, December 1999 • Boykov, Y.; Veksler, O.; Zabih, R.; Fast approximate energy minimization via graph cuts, Pattern Analysis and Machine Intelligence, IEEE Transactions on Volume 23,  Issue 11,  Nov. 2001 Page(s):1222 - 1239

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