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Object Based Stereoscopic Video Coding

image scene analysis depth

Definition: Object-based coding techniques have the ability to describe a scene in a structural way and to convey depth information that can be computed directly from the images.

Object based coding has long attracted considerable attention as a promising alternative to block-based encoding, achieving excellent performance and producing fewer annoying effects. Furthermore, important image areas such as facial details in face to face communications can be reconstructed with a higher image quality than with block-oriented hybrid coding. In addition, the ability of object based coding techniques to describe a scene in a structural way, in contrast to traditional waveform-based coding techniques, opens new areas of applications. Video production, realistic computer graphics, multimedia interfaces and medical visualization are some of the applications that may benefit by exploiting the potential of object based schemes. Object based approaches applied in coding of stereo image sequences have the additional benefit of conveying depth information which may be computed directly from the images. Using the depth information the scene may be separated in layers and depth keying is possible.

Also, accurate 3D modeling of the scene structure may be achieved. The main problem in object based analysis is the automatic extraction and modeling of objects directly from the image intensities. This task may require complex image analysis techniques to segment the scene into homogeneous regions or even user interaction so that image regions correspond to real objects on the scene.

Figure 1 illustrates the basic structure of an object-based stereoscopic image coding scheme. The encoder consists of an analysis part and a synthesis part. The analysis part aims to subdivide the scene into a set of objects representing each one by a set of parameters: shape or boundary, motion, structure or depth and texture or colour. These parameters are encoded and transmitted to the decoder where the decoded parameters are then used to synthesize an approximation of the original images. The analysis phase is the most sophisticated one, consisting of image segmentation and motion/structure estimation.

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