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Yayın A survey of algorithms and architectures for H.264 sub-pixel motion estimation(World Scientific, 2012-05) Fatemi, Mohammad Reza Hosseiny; Ateş, Hasan Fehmi; Salleh, Rosli BinThis paper reviews recent state-of-the-art H. 264 sub-pixel motion estimation (SME) algorithms and architectures. First, H.264 SME is analyzed and the impact of its functionalities on coding performance is investigated. Then, design space of SME algorithms is explored representing design problems, approaches, and recent advanced algorithms. Besides, design challenges and strategies of SME hardware architectures are discussed and promising architectures are surveyed. Further perspectives and future prospects are also presented to highlight emerging trends and outlook of SME designs.Yayın Spectral coding of mesh geometry with a hierarchical set partitioning algorithm(Spie-Int Soc Optical Engineering, 2008) Konur, Umut; Bayazıt, Uluğ; Ateş, Hasan Fehmi; Gürgen, Sadık FikretThis work proposes a progressive mesh geometry coder, which expresses geometry information in terms of spectral coefficients obtained through a transformation and codes these coefficients using a hierarchical set partitioning algorithm that assigns right priorities to those coefficients at all bit planes. The spectral transformation used is the one proposed in [8] where the spectral coefficients are obtained by projecting the mesh geometry on an orthonormal basis determined by mesh topology. The set partitioning method used in coding, treats spectral coefficients belonging to the three spatial coordinates with the right priority at all bit planes and realizes a truly embedded system by achieving implicit bit allocation via joint coding the zeroes of coefficients at the bit planes. The experiments performed on common irregular meshes reveal that the rate-distortion performance of the coder is significantly superior to the coding system proposed in [8].Yayın Decoder-side super-resolution and frame interpolation for improved H.264 video coding(IEEE, 2013) Ateş, Hasan FehmiIn literature decoder-side motion estimation is shown to improve video coding efficiency of both H.264 and HEVC standards. In this paper we introduce enhanced skip and direct modes for H.264 coding using decoder-side super-resolution (SR) and frame interpolation. P-and B-frames are downsampled and H.264 encoded at lower resolution (LR). Then reconstructed LR frames are super-resolved using decoder-side motion estimation. Alternatively for B-frames, bidirectional true motion estimation is performed to synthesize a B-frame from its reference frames. For P-frames, bicubic interpolation of the LR frame is used as an alternative to SR reconstruction. A rate-distortion optimal mode selection algorithm determines for each MB which of the two reconstructions to use as skip/direct mode prediction. Simulations indicate an average of 1.04 dB PSNR improvement or 23.0% bitrate reduction at low bitrates when compared to H.264 standard. Average PSNR gains reach as high as 3.95 dB depending on the video content and frame rate.Yayın Rate-distortion and complexity joint optimization for fast motion estimation in H.264 video coding(IEEE, 2006) Ateş, Hasan Fehmi; Kanberoğlu, Berkay; Altunbaşak, YücelH.264 video coding standard offers several coding modes including inter-prediction modes that use macroblock partitions with variable block sizes. Choosing a rate-distortion optimal mode among these possibilities contributes significantly to the superior coding efficiency of the H.264 encoder. Unfortunately, searching for optimal motion vectors of each possible subblock incurs a heavy computational cost. In this paper, in order to reduce the complexity of integer-pel motion estimation, we propose a rate-distortion and complexity joint optimization method that selects for each MB a subset of partitions to evaluate during motion estimation. This selection is based on simple measures of spatio-temporal activity within the MB. The procedure is optimized to minimize mode estimation error at a certain level of computational complexity. Simulation results show that the algorithm speeds up the motion estimation module by a factor of up to 20 with little loss in coding efficiency.Yayın Disaster damage assessment of buildings using adaptive self-similarity descriptor(2016-08) Kahraman, Fatih; İmamoğlu, Mümin; Ateş, Hasan FehmiAssessment of damage caused by a disaster is significant for coordinating emergency response teams and planning emergency aid. In this letter, a robust method for rapid building damage assessment is proposed using pre- and postevent EO images and building footprints. The method uses a local self-similarity descriptor (SSD) for change detection in buildings, which is shown to be robust against variations in global illumination and small local deformations. The use of building footprints helps reduce the false alarms due to changes in nonbuilding areas. Footprint is also used to differentiate small and large buildings, extract the boundary region of a building, and adapt the descriptor computation accordingly. It is shown that the adaptive SSD provides a more accurate measure of local damage on the building. The 2010 Haiti Earthquake and Typhoon Haiyan 2013 Philippines are analyzed with the proposed method, and 75/82% true positive rate and 25/15% false positive rate are obtained for detection of collapsed buildings with respect to the ground truth data of UNITAR/UNOSAT and HOT.Yayın Low complexity inter-mode selection for H.264(IEEE, 2006) Ba, Seydou Nourou; Altunbaşak, Yücel; Ateş, Hasan FehmiThe coding efficiency of the H.264/AVC standard enables the transmission of high quality video over bandwidth limited networks. Due to the use of multiple Macroblock (MB) partitions, the Motion estimation module has extremely high complexity that makes it unpractical for most real-time applications on resource-limited platforms such as hand held devices. In this paper we propose a novel algorithm that significantly reduces the encoding complexity while maintaining high rate distortion performance. The proposed method reduces the Motion estimation (ME) computational complexity by accurately predicting the optimal MB partitions and restricting the number of candidate modes based on a-priori probabilities computed from spatio-temporal information. The experimental results show that the speed up of UmHexagonS [1] (one of the most efficient ME algorithms) can be doubled while maintaining the coding efficiency of Full Search.Yayın Spherical coding algorithm for wavelet image compression(IEEE-Inst Electrical Electronics Engineers Inc, 2009-05) Ateş, Hasan Fehmi; Orchard, Michael T.In recent literature, there exist many high-performance wavelet coders that use different spatially adaptive coding techniques in order to exploit the spatial energy compaction property of the wavelet transform. Two crucial issues in adaptive methods are the level of flexibility and the coding efficiency achieved while modeling different image regions and allocating bitrate within the wavelet subbands. In this paper, we introduce the "spherical coder," which provides a new adaptive framework for handling these issues in a simple and effective manner. The coder uses local energy as a direct measure to differentiate between parts of the wavelet subband and to decide how to allocate the available bitrate. As local energy becomes available at finer resolutions, i.e., in smaller size windows, the coder automatically updates its decisions about how to spend the bitrate. We use a hierarchical set of variables to specify and code the local energy up to the highest resolution, i.e., the energy of individual wavelet coefficients. The overall scheme is nonredundant, meaning that the subband information is conveyed using this equivalent set of variables without the need for any side parameters. Despite its simplicity, the algorithm produces PSNR results that are competitive with the state-of-art coders in literature.Yayın 3-D Mesh geometry compression with set partitioning in the spectral domain(IEEE-INST Electrical Electronics Engineers Inc, 2010-02) Bayazıt, Uluğ; Konur, Umut; Ateş, Hasan FehmiThis paper explains the development of a highly efficient progressive 3-D mesh geometry coder based on the region adaptive transform in the spectral mesh compression method. A hierarchical set partitioning technique, originally proposed for the efficient compression of wavelet transform coefficients in high-performance wavelet-based image coding methods, is proposed for the efficient compression of the coefficients of this transform. Experiments confirm that the proposed coder employing such a region adaptive transform has a high compression performance rarely achieved by other state of the art 3-D mesh geometry compression algorithms. A new, high-performance fixed spectral basis method is also proposed for reducing the computational complexity of the transform. Many-to-one mappings are employed to relate the coded irregular mesh region to a regular mesh whose basis is used. To prevent loss of compression performance due to the low-pass nature of such mappings, transitions are made from transform-based coding to spatial coding on a per region basis at high coding rates. Experimental results show the performance advantage of the newly proposed fixed spectral basis method over the original fixed spectral basis method in the literature that employs one-to-one mappings.Yayın Wavelet image coding using the spherical representation(IEEE, 2005) Ateş, Hasan Fehmi; Orchard, Michael T.In this paper, we introduce the "spherical representation", which provides a new adaptive framework for modeling and coding the image information in wavelet subbands. Based on this representation, a practical coding algorithm is developed. This coder uses local energy as a direct measure to differentiate between parts of the wavelet subband and to decide how to allocate the available bitrate. As local energy becomes available at finer resolutions, i.e. in smaller size windows, the coder automatically updates its decisions about how to spend the bitrate. We use a hierarchical set of variables to specify and code the local energy up to the highest resolution, i.e. the energy of individual wavelet coefficients. The overall scheme is nonredundant, meaning that the subband information is conveyed using this equivalent set of variables without the need for any side parameters. Despite its simplicity, the algorithm produces PSNR results that are competitive with the state-of-art coders in literature.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.
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