Object-oriented Analysis-synthesis Coding Based on Source Models of Moving 2 D - and 3d-objects

Abstract

For encoding moving images at very low bit rates objectoriented analysis-synthesis coding using source models of moving 2 D and 3D-objects has been investigated. According to this coding concept each moving object of an image is described and encoded by three parameter sets defining the motion, the shape and the surface colour of the moving object The parameters to be coded are dependent on the source model being applied. Thus, the coding efficiency of objectoriented analysis-synthesis coding can be evaluated by comparing the encoded parameter bit rates for a fixed picture quality. The results obtained with source models of moving 213and 3D-objects are compared to those of a standard H.261 coder at a bit rate of 64 kbit/s. The source models of flexible 2 D and rigid 3D-objects are more efficient than source models which are based on rigid 2D-objects or on moving blocks as in the case of a H.261 coder. 1. I N T R O D U C T I O N In order to encode moving video signals at 64 kbit/s transmission rate the standardized hybrid coding technique H.261 subdivides each image of a sequence into blocks of 1 6 x 1 6 picture elements (pels) and encodes each block by motion compensated predictive and transform coding [1]. Thus this coding technique is based on the source model of moving square blocks which can lead to visible distortions known as blocking and mosquito effects. To avoid these image distortions object-oriented analysis-synthesis coding [2] has been proposed. This coding technique is based on the source model of moving objects instead of moving square blocks. Each object is described and encoded by three parameter sets defining the motion, shape and surface colour of the object. The parameter sets to be coded vary with the kind of object model. Three kinds of object models have been invetigated, rigid 2D-objects [3], flexible 2D-objects [4] and rigid 3 D objects [5]. In order to evaluate the coding efficiency of object-oriented analysis-synthesis coding the encoded parameter bit rates of the cited source models are compared at a fixed picture quality measured by the signal-to-noise ratio. After a short explanation of the basic components of an object-oriented analysis-synthesis coder in section 2 the coding of the parameter sets is described in section 3. Finally the influence of the various source models on the coding efficiency is discussed in section 4. 2. GENERAL S T R U C T U R E O F A N O B J E C T O R I E N T E D A N A L Y S I S S Y N T H E S I S C O D E R The block diagram of an object oriented analysis-synthesis coder is shown in Fig.l . Instead of a frame memory as in block-oriented coding techniques object-oriented coding requires a memory to store the parameter sets A = {Aj}, M = {Mj}, S = {Sj} defining the motion Aj, shape Mj and colour S; of each moving object i. The memory for object parameters of the coder and decoder contains the same parameter informations and allows the coder and decoder to reconstruct a transmitted image by image synthesis. The reconstructed image V k is displayed at the decoder and used for image analysis of the next input image I k+ I at the coder. The task of the image analysis block in Fig. 1 is to estimate the parameter sets A;, M;. Sj for each object i of the next input image Ik+i by use of the reconstructed image I'k. At the output of the image analyis block the parameter sets Ai, Mj, Sj are available in PCM representation. Image analysis distinguishes between two types of objects. Model Compliance objects (MC-objects) can be reconstructed by transmitting only the motion Aj and shape Mj parameter sets and using the colour Si parameter set stored in the memory. Model failure objects (MF-objects) are image areas where the motion description by the source model fails. MF-objects are encoded by the shape Mi and colour Sj parameter sets, see Table 1.

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Cite this paper

@inproceedings{Musmann2008ObjectorientedAC, title={Object-oriented Analysis-synthesis Coding Based on Source Models of Moving 2 D - and 3d-objects}, author={Hans Georg Musmann}, year={2008} }