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Yayın Decoder side true motion estimation for very low bitrate b-frame coding(IEEE, 2011) Ateş, Hasan Fehmi; Çizmeci, BurakIn H.264 standard, coding of motion vectors constitutes a significant portion of total bitrate especially at low bitrate regimes. This is because differential coding of motion vectors is inefficient when the bit budget is very low. In this paper, we propose a novel estimation and coding algorithm for motion vectors of B-frames at very low bitrates. In this method, the encoder selects the optimal motion vector from a limited set of candidate vectors that are determined at the decoder side using true motion estimation. Since these candidate vector sets are fixed by the decoder for each macroblock, there is no need for explicit coding of motion information, which reduces the bitrate required for coding. Also, true motion vector estimates are used for improved direct mode coding in B-frames. The algorithm provides an average of 0.68 dB PSNR gain for B-frames when compared to the reference H.264 results at the same bitrates. Simulation results also indicate significant improvement in visual quality of the compressed B-frames.Yayın Occlusion aware motion compensation for video frame rate up-conversion(2010) Çizmeci, Burak; Ateş, Hasan FehmiSince the emergence of high definition (HD) display technologies, video standards conversion problem has become an important issue in storage, transmission and display of video content. Video frame rate up-conversion (FRUC) is considered as a standard task for today's HD displays because these displays reach high refresh rates of at least 100/120 Hz and low video frame rates should be pulled up by a factor of 2 or more before display. Motion compensated FRUC techniques are proposed to avoid motion blur and motion judder at high refresh rates, but these techniques suffer from spatial inconsistencies and artifacts especially in occluded regions of the interpolated frames. This paper introduces a new video FRUC method that aims to remove both motion judder and occlusion artifacts and generate smooth object motion for high quality displays. An occlusion adaptive overlapped block motion compensation (OBMC) technique is proposed, which provides spatio-temporally consistent frame interpolation. Covered/uncovered regions are detected by analyzing the discontinuities of the motion vector field. The occlusion regions are interpolated using this covered/uncovered decision and a new error metric that measures spatial consistency. Compared to existing methods, the proposed algorithm achieves FRUC with fewer artifacts and better spatial resolution especially in occluded areas.Yayın True motion estimation for video frame rate up-conversion(Işık Üniversitesi, 2009) Çizmeci, Burak; Ateş, Hasan Fehmi; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıSince the invention of high definition display technologies, video standards conversion problem has become an important task to store, transmit and display new video formats. One of the standards conversion issue, video frame rate up-conversion (FRUC) should be considered as an important problem for high definition displays because these displays reach high refresh ates up to 100 Hz and low video frame rates should be increased before displaying. The solutions generated by conventional FRUC techniques cause artifacts such as jerkie motion and judder effect on the screen. The objective of this thesis is to remove judder and occlusion artifacts and generate a smooth object motion for high definition displays. In order to solve the problem, this thesis describes a multi-stage motion vector (MV) post-processing technique for true motion estimation and proposes a new video frame rate up-conversion method with occlusion adaptive overlapped block motion compensation, which increases the temporal resolution without loss of spatial resolution and consistency. Conventional block matching algorithms yields us unreliable MVs which should be post-processed in the refinement stages to get a consistent MV field in spatial domain. Relations between neighboring MVs are utilized to detect occlusion regions. Overlapped Block Motion Comppensation (OBMC) is adapted to these problematic regions in order to reduce halo artifacts caused by occlusion. Compared to existing methods, the proposed algorithm achieves FRUC with reduced loss of spatiaal resolution and reduced amount of artifacts.
