Object-based Analysis-synthesis Research Articles

Circle-tangent interpolation of vertices for measurement value representation and shape approximation in object video coding

Abstract A circle-tangent interpolation of vertices and simple algorithms to find these vertices are presented which perform the description of shapes. These shapes are parts of the object-based analysis-synthesis code for image sequences. The algorithms for the shape approximation presented here take advantage of the qualities of the circle-tangent interpolation. The number of the vertices required can be reduced by about 23%. Furthermore, the advantage of the circle-tangent interpolation for the representation of measuring values is shown.

Automatic adaptation of a face model in a layered coder with an object-based analysis-synthesis layer and a knowledge-based layer

Abstract The topic of investigation was the extension of a generic object-based analysis-synthesis coder (OBASC) using the source model of ‘moving flexible 3D objects’ for the encoding of moving images at very low data rates to a knowledge-based coder in case scene-specific knowledge can be acquired. According to the coding concept, the OBASC describes and encodes each moving object of an image sequence by three parameter sets defining its motion, shape and surface color. The parameter sets of each object are obtained by image analysis. Using the coded parameter sets, an image can be synthesized by model-based image synthesis. The coder switches to a knowledge-based coder as soon as scene-specific knowledge can be acquired. In the example given in this paper, an algorithm tries to detect faces within moving objects using template matching and feature extraction techniques. If a face is detected, the face model Candide is adapted to the image sequence and integrated into the 3D model object describing the moving object. Due to this knowledge of the scene, the head and shoulders scene can be more efficiently modeled and encoded. Furthermore, the knowledge of the scene contents is used for controlling the coder. When compared to OBASC, the knowledge-based coder reduces the bit-rate required for encoding head and shoulder scenes by 17%.

Shape estimation of articulated 3D objects for object-based analysis-synthesis coding (OBASC)

Abstract This paper investigates shape estimation of articulated 3D objects for object-based analysis-synthesis coding based on the source model of ‘moving articulated 3D objects’. For shape estimation three steps are applied: shape-initialization, object-articulation and shape-adaptation. Here, a new algorithm for object-articulation is introduced. Object-articulation subdivides a rigid model object represented by a mesh of triangles into flexibly connected model object-components. For object articulation, neighboring triangles which exhibit similar 3D motion during the image sequence are clustered into patches. These patches are considered to be the model object-components. For 3D motion estimation of a single triangle, a more reliable algorithm is proposed. The reliability is measured by the probability of convergency to correct parameters. For improving the reliability both, a more robust technique is applied and the triangle and its neighborhood are evaluated by the estimation algorithm. For clustering, a frame to frame clustering method which considers clustering results obtained in previous frames is presented. The developed algorithm for object-articulation is incorporated in OBASC. Typical videophone test sequences were applied. Compared to OBASC based on the source model of ‘moving rigid 3D objects’, the transmission rate decreases from 63.5 to 53 kbit/s at a fixed image quality measured by SNR. Furthermore, a realistic object articulation of a model object ‘body’ into object-components ‘head’ and ‘shoulders’ can be achieved without a priori knowledge about the scene content.

Redundancy reducing coding of moving object shapes

Abstract A redundancy reducing technique for coding of object shapes in image sequences is presented. Polygon-spline approximation as known from object-based analysis-synthesis coding is used as a basis. A parametric hexagonal coordinate system sis introduced in place of the cartesian one. The range of relative coordinates is limited. By these two methods the data rate required for coding the shapes is decreased by about 13%. When additionally using temporal prediction, by exploiting the fact that the slope of an object shape does not differ so much in time, a total decrease of about 28% is achieved.

A layered coding system for very low bit rate video coding

Abstract Known coding techniques for transmitting moving images at very low bit rates are explained by the source models on which these coding techniques are based. It is shown that with motion-compensated hybrid coding, object-based analysis-synthesis coding, knowledge-based coding and semantic coding, there is a consistent development of source models. In consequence these coding techniques can be combined in a layered coding system. From experimental results obtained for object-based analysis-synthesis, coding estimates for the coding efficiency of such a layered coding system are derived using head and shoulder video telephone test sequences. It is shown that an additional compression factor of about 3 can be expected with such a complex layered coding system, when compared to block-based hybrid coding.

Estimation of point light source parameters for object-based coding

Abstract In this paper, the source model of moving rigid 3D objects of an object-based analysis-synthesis coder (OBASC) is extended from diffuse to non-diffuse illumination introducing the explicit illumination model of a distant point light source and ambient diffuse light. For each image of a real image sequence containing moving objects, first, shape and 3D motion parameters describing the objects are estimated assuming an ellipsoid-like smooth shape. Then, the illumination parameters are estimated by a fast iterative maximum-likelihood Gauβ-Newton estimation method. Typically, the illumination parameters converge after very few images close to the true ones. The accurateness depends on the amount of object rotation and the correctness of the shape assumptions. For a real image sequence showing a textured ball covering 20% of image area, rotating about 10 ° per frame, and illuminated by spot and ambient light, the extension of the source model reduces the model failures from 9.9% of the image area to 6.7%. In the area of model failures, the image synthesized from the source model parameters differ significantly from the real image. In this early experiment, source model parameters are coded losslessly. Since model failures are expensive by means of bit-rate, a significant reduction of bit-rate can be expected.

Object-based analysis-synthesis coding of image sequences at very low bit rates

An object-based analysis-synthesis image sequence coder for transmission bit rates between 8 and 16 kbit/s is presented. Each moving object is described by three sets of parameters defining its shape, motion, and colour. Coding is based on the source model of flexible 2D objects which move translationally in the image plane, as it has been used in an implementation for a 64 kbit/s ISDN videophone by Hotter (1990). In order to cut down the bit rate from 64 kbit/s to 8 kbit/s, QCIF image resolution instead of CIF resolution is applied. Image analysis and coding of object parameters have been adapted to the reduced resolution and to the changed parameter statistics, respectively. In addition to Hotter's coder, predictive coding is used for encoding polygons and splines to improve the coding efficiency of shapes. Vector quantization is applied instead of DCT for coding the luminance and chrominance parameters of the object textures. Uncovered background regions are encoded by applying adaptive prediction from either the neighbouring static background or a special background memory. Experimental results, obtained by computer simulations, confirm that the presented coding algorithm is a promising scheme for the application at extremely low transmission bit rates. This is shown by comparing the picture qualities obtained with the presented algorithm and a block-based hybrid-DCT scheme corresponding to H.261/RM8 at 11 kbit/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Prototype prediction for colour update in object-based analysis-synthesis coding

In an object-based analysis-synthesis coder each image of an image sequence is subdivided into arbitrarily shaped moving objects. The objects are described by three parameter sets defining their motion, shape and colour, where the colour parameters denote the luminance and chrominance values of the object surface. In order to increase the efficiency of the coder, a predictive technique for the coding of colour parameters is presented using image pattern prototypes for prediction. The prototypes are extracted from previously coded images and identically stored at the coder and the decoder. They can be used for the prediction of the colour parameters of an object by applying a suitably defined mapping function. The prediction error is coded by an adaptive combination of DCT and intraframe DPCM. For the reconstruction of the colour parameters at the decoder the address of the image pattern prototype and the parameters of the mapping function have to be transmitted as side information. Prototype prediction is only applied, when its data rate is lower than that of an extended hybrid scheme. At a transmission data rate of 61 kbit/s prototype prediction increases the PSNR by 2 dB in the areas of colour update. >

Object-based analysis-synthesis coding based on the source model of moving rigid 3D objects

The topic of investigation was object-based analysis-synthesis coding (OBASC) using the source model of ‘moving rigid 3D objects’ for the encoding of moving images at very low data rates. According to the coding concept, each moving object of an image is described and encoded by three parameter sets defining its motion, shape and surface color. The parameter sets of each object are obtained by image analysis. They are coded using an object-dependent parameter coding. Using the coded parameter sets, an image can be synthesized by model-based image synthesis. In comparison to block-based hybrid coding, OBASC requires the additional transmission of shape parameters. The transmission of shape information avoids the mosquito and block artifacts of a block-based coder. Furthermore, important areas such as facial areas can be reconstructed with a significant image quality improvement. OBASC based on the source models of ‘moving flexible 2D objects’ and of ‘moving rigid 3D objects’ gives almost identical image quality for the same data rate. Therefore the use of more advanced source models like flexible 3D objects or 3D face models is expected to further improve image quality.

Object-based analysis-synthesis coding (OBASC) based on the source model of moving flexible 3-D objects

This correspondence investigates object-based analysis-synthesis coding (OBASC) for the encoding of moving images at very low data rates. According to the source model, each moving object of an image is described and encoded by three parameter sets defining its motion, shape, and surface color. The parameter sets of each object are obtained by model-based image analysis. They are coded by an object-dependent parameter coding. Using the coded parameter sets, an image can be synthesized by model-based image synthesis. Here, OBASC based on the source model of "moving flexible 3-D objects with 3-D motion" (F3D) is introduced. The efficiency of this source model F3D is compared to the efficiency of OBASC based on the source model of "moving rigid 3-D objects with 3-D motion" (R3D). Compared to R3D, F3D requires the additional transmission of flexible-shape parameters. Therefore, the source model F3D is only applied in those areas of the image which cannot be described by the source model R3D. The new source model F3D reduces the bit rate from 64 to 56 kb/s, providing the same picture quality measured by the SNR of the encoded color parameters.