Pierangela Cicconi

Efficient region-based motion estimation and symmetry oriented segmentation for image sequence coding

In the paper an efficient coding system for very low bit rates is presented. It is characterized by three operating modes. The intraframe mode combines image segmentation and an efficient luminance representation focalized on the concept of symmetry. The motion compensated mode is based on an adaptive motion representation which provides a good trade-off between the cost of parameter transmission and the quality of prediction. The obtained motion vector field is used for the reconstruction in the predicted mode. Experimental results are given on four test sequences. Simulations show good performance of the coding system both in terms of PSNR and bitrate. In particular, experiments show that the system is capable of working at around 24 kbit/sec with good quality for head-and-shoulder sequences. With more complex sequences, 50 kbit/sec are reached with acceptable degradation of the reconstructed images. >

New trends in image data compression

This paper gives an overview of a number of advanced techniques for image compression, which are under investigation in the Signal Processing Laboratory at the Swiss Federal Institute of Technology of Lausanne. Various applications ranging from High definition television (HDTV) to multimedia will be discussed. In particular, systems based on subband decomposition, edge based representation, as well as symmetries will be presented.

Symmetry-based image segmentation

In this work, we present a technique which suggests the use of symmetry to reduce the redundancy in images. A symmetry-based image segmentation and coding scheme is described. A segmentation technique is analyzed, and applied on natural images, performing their efficient partition. In order to find symmetries in regions of any shape, the concept of axes of symmetry is generalized to skeletons of symmetry, dividing the regions into two symmetric subparts by the introduction of the Medial Axis Transformation of the regions. Each subpart of the regions is then linearly predicted with respect to the skeletons. An efficient coding strategy specifying the shape and the luminance of the regions is described. Results on natural images show that the described technique outperforms the more classical second generation image coding methods in terms of visual quality.

Symmetry-based image coding

A novel coding technique which proposes the use of symmetry to reduce redundancy in images is presented. Axes of symmetry are extracted using the Principal Axes of Inertia theory and the technique is extended to non-symmetric images by the introduction of a Coefficient of Symmetry. One part of the images is then linearly predicted with respect to the chosen axis. The method is implemented in a block-based fashion in order to adapt to local symmetries on the image data. An image representation and a coding strategy is illustrated, and results are presented on real static images.