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Wavelet based Video coding with optical flow for motion compensation
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Electronics and Telecommunications.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]

In broadcasting environments intra-only video coding with JPEG 2000 has shown to provide many desired features along with high picture quality. However, there is no exploitation of temporal redundancy, which can reduce the bit rate while maintaining the quality. Optical flow algorithms are designed to find the apparent movement of brightness in an image, and can be used to estimate the motion of each pixel between consecutive images. This thesis explores the performance of a hybrid video codec that uses the ’Classic+NL’ optical flow algorithm for motion compensation and JPEG 2000 for encoding the estimation error. The motion estimation proved to be inaccurate at the edges of objects. This can cause high frequency components in the residue image, which will decrease the efficiency of JPEG 2000. Occluded regions will also have poor estimation, as they are not present in the previous frame. Since noise is not considered when the optical flow is calculated, the energy of the noise may increase after motion compensation. Without addressing these issues, optical flow algorithms are not well suited for motion estimation in hybrid video codecs. Even with the inaccurate motion compensation performed by the optical flow algorithm, there was an overall reduction in bit rate of 18.8%, compared to intra-only coding with JPEG 2000. The performance was highly content dependent, ranging from a reduction of 90% to an increase of 27%. The reduction comes at a cost of increased delay, higher complexity, vulerability to transmission errors, and a lack of a constant bit stream. The proposed hybrid codec is therefore not suited to replace intra-only coding with JPEG 2000 in contribution environments.

Place, publisher, year, edition, pages
Institutt for elektronikk og telekommunikasjon , 2011. , 103 p.
Keyword [no]
ntnudaim:6211, MTEL elektronikk, Digital kommunikasjon
URN: urn:nbn:no:ntnu:diva-14175Local ID: ntnudaim:6211OAI: diva2:448152
Available from: 2011-10-14 Created: 2011-10-14

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