Change search
Refine search result
1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Barry, Ousmane
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Liu, Du
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Richter, Stefan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Robust Motion-Compensated Orthogonal Video Coding Using EBCOT2010In: Proceedings - 4th Pacific-Rim Symposium on Image and Video Technology, PSIVT 2010, IEEE , 2010, p. 264-269Conference paper (Refereed)
    Abstract [en]

    This paper proposes a rate-distortion control for motion-compensatedorthogonal video coding schemes and evaluates its robustness to packet loss as faced in, e.g., IP networks. The robustness of standard hybrid video coding is extensively studied in the literature. In contrast, motion-compensated orthogonal subbands offer important advantages and new features for robust video transmission. In this work, we utilize so-called uni-directional motioncompensated orthogonal transforms in combination with entropy coding similar to EBCOT known from JPEG2000.The approach provides a flexible embedded structure and allows flexible rate-distortion optimization. Moreover, it may even permit separate encoding and rate control. The proposed rate-distortion control takes channel coding into account and obtains a preemptively protected representation. Our implementation is based on repetition codes, adapted to the channel condition, and improves the PSNR significantly. The optimization requires an estimate of the packet loss rate at the encoder and shows moderate sensitivity to estimation errors.

  • 2.
    Liu, Du
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Orthonormal Motion-Adaptive Transforms for Image Sequences2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In this thesis, we propose and discuss a class of motion-adaptive transforms (MAT) to describe the temporal correlation in image sequences for compression. The temporal correlation is based on motion models, and undirected graphs are used to represent this correlation in image sequences. The transforms are adaptive to general motion fields. Hence, they avoid the predict-update mismatch of the classic block-motion lifting schemes in processing connected and disconnected pixels. Moreover, the proposed transforms are orthonormal for general motion field, and thus, they permit energy conservation and perfect reconstruction.

    As we represent the motion-connected signals by graphs, we introduce a graph-based covariance matrix model and use the associated eigenvector matrix for compression. As the proposed covariance model is closely related to the graph, the relation between the covariance matrix and theLaplacian matrix is studied and the associated eigenvector matrices are discussed. The class of MAT is constructed by using so-called scale factors.We show that the scale factors determine a relevant subspace of the signal representation.Hence, we propose a subspace-constrained transform, which achieves optimal energy compaction given the subspace constraint. On the other hand, the resulting basis vectors are signal dependent.

    To construct practical transforms without using covariance matrices, we consider two types of incremental transforms over graphs, namely the uni-directional orthogonal transform (Uni-OT) and the bidirectional orthogonal transform (Bi-OT). In addition, fractional-pel MAT is proposed to further extend the class of MAT. Our fractional-pel MAT can incorporate a general interpolation filter into the basis vectors, while offering perfect reconstruction, orthogonality, and improved coding efficiency.

  • 3.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Energy Compaction on Graphs for Motion-Adaptive Transforms2015In: Data Compression Conference Proceedings, 2015, p. 457-Conference paper (Refereed)
    Abstract [en]

    It is well known that the Karhunen-Loeve Transform (KLT) diagonalizes the covariance matrix and gives the optimal energy compaction. Since the real covariance matrix may not be obtained in video compression, we consider a covariance model that can be constructed without extra cost. In this work, a covariance model based on a graph is considered for temporal transforms of videos. The relation between the covariance matrix and the Laplacian is studied. We obtain an explicit expression of the relation for tree graphs, where the trees are defined by motion information. The proposed graph-based covariance is a good model for motion-compensated image sequences. In terms of energy compaction, our graph-based covariance model has the potential to outperform the classical Laplacian-based signal analysis.

  • 4.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Graph-Based Construction and Assessment of Motion-Adaptive Transforms2013Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose two algorithms to construct motion-adaptive transforms that are based on vertex-weighted graphs. The graphs are constructed by motion vector information. The weights of the vertices are given by scale factors that are used to accommodate proper concentration of energy in transforms. The vertex-weighted graph defines a one dimensional linear subspace. Thus, our transform basis is subspace constrained. We propose two algorithms. The first is based on the Gram-Schmidt orthonormalization of the discrete cosine transform (DCT) basis. The second combines the rotation of the DCT basis and the Gram-Schmidt orthonormalization. We assess both algorithms in terms of energy compaction. Moreover, we compare to prior work on graph-based rotation of the DCT basis and on so-called motion-compensated orthogonal transforms (MCOT). In our experiments, both algorithms outperform MCOT in terms of energy compaction. However, their performance is similar to that of graph-based rotation of the DCT basis.

  • 5.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Graph-Based Rotation of the DCT Basis for Motion-Adaptive Transforms2013In: 2013 20TH IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING (ICIP 2013), IEEE conference proceedings, 2013, p. 1802-1805Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider motion-adaptive transforms that are based on vertex-weighted graphs. The graphs are constructed by motion vector information and the weights of the vertices are given by scale factors, where the scale factors are used to control the energy compaction of the transform. The vertex-weighted graph defines a one dimensional linear subspace. Thus, our transform basis is subspace constrained. To find a full transform matrix that satisfies our subspace constraint, we rotate the discrete cosine transform (DCT) basis such that the first basis vector matches the subspace constraint. Since rotation is not unique in high dimensions, we choose a simple rotation that only rotates the DCT basis in the plane which is spanned by the first basis vector of the DCT and the subspace constraint. Experimental results on energy compaction show that the motion-adaptive transform based on this rotation is better than the motion-compensated orthogonal transform based on hierarchical decomposition while sharing the same first basis vector.

  • 6.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Motion-Adaptive Transforms Based on the Laplacian of Vertex-Weighted Graphs2014Conference paper (Refereed)
    Abstract [en]

    We construct motion-adaptive transforms for image sequences by using the eigenvectors of Laplacian matrices defined on vertex-weighted graphs, where the weights of the vertices are defined by scale factors. The vertex weights determine only the first basis vector of the linear transform uniquely. Therefore, we use these weights to define two Laplacians of vertex-weighted graphs. The eigenvectors of each Laplacian share the first basis vector as defined by the scale factors only. As the first basis vector is common for all considered Laplacians, we refer to it as subspace constraint. The first Laplacian uses the inverse scale factors, whereas the second utilizes the scale factors directly. The scale factors result from the assumption of ideal motion. Hence, the ideal unscaled pixels are equally connected and we are free to form arbitrary graphs, such as complete graphs, ring graphs, or motion-inherited graphs. Experimental results on energy compaction show that the Laplacian which is based on the inverse scale factors outperforms the one which is based on the direct scale factors. Moreover, Laplacians of motion-inherited graphs are superior than that of complete or ring graphs, when assessing the energy compaction of the resulting motion-adaptive transforms.

  • 7.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Motion-Adaptive Transforms based on Vertex-Weighted Graphs2013In: 2013 Data Compression Conference (DCC), IEEE Computer Society, 2013, p. 181-190Conference paper (Refereed)
    Abstract [en]

    Motion information in image sequences connects pixels that are highly correlated. In this paper, we consider vertex-weighted graphs that are formed by motion vector information. The vertex weights are defined by scale factors which are introduced to improve the energy compaction of motion-adaptive transforms. Further, we relate the vertex-weighted graph to a subspace constraint of the transform. Finally, we propose a subspace-constrained transform (SCT) that achieves optimal energy compaction for the given constraint. The subspace constraint is derived from the underlying motion information only and requires no additional information. Experimental results on energy compaction confirm that the motion-adaptive SCT outperforms motion-compensated orthogonal transforms while approaching the theoretical performance of the Karhunen Loeve Transform (KLT) along given motion trajectories.

  • 8.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Sound and Image Processing (Closed 130101). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    Video coding using multi-reference motion-adaptive transforms based on graphs2016In: 2016 IEEE 12th Image, Video, and Multidimensional Signal Processing Workshop, IVMSP 2016, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    The purpose of the work is to produce jointly coded frames for efficient video coding. We use motion-adaptive transforms in the temporal domain to generate the temporal subbands. The motion information is used to form graphs for transform construction. In our previous work, the motion-adaptive transform allows only one reference pixel to be the lowband coefficient. In this paper, we extend the motion-adaptive transform such that it permits multiple references and produces multiple lowband coefficients, which can be used in the case of bidirectional or multihypothesis motion estimation. The multi-reference motion-adaptive transform (MRMAT) is always orthonormal, thus, the energy is preserved by the transform. We compare MRMAT and the motion-compensated orthogonal transform (MCOT) [1], while HEVC intra coding is used to encode the temporal subbands. The experimental results show that MRMAT outperforms MCOT by about 0.6dB.

  • 9.
    Liu, Du
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Flierl, Markus
    KTH, School of Electrical Engineering (EES), Sound and Image Processing (Closed 130101).
    Video coding with adaptive motion-compensated orthogonal transforms2012In: / [ed] Domanski, M; Grajek, T; Karwowski, D; Stasinski, R, IEEE , 2012, p. 293-296Conference paper (Refereed)
    Abstract [en]

    Well-known standard hybrid coding techniques utilize the concept of motion-compensated predictive coding in a closed-loop. The resulting coding dependencies are a major challenge for packet-based networks like the Internet. On the other hand, subband coding techniques avoid the dependencies of predictive coding and are able to generate video streams that better match packet-based networks. An interesting class for subband coding is the so-called motion-compensated orthogonal transform. It generates orthogonal subband coefficients for arbitrary underlying motion fields. In this paper, a theoretical signal model based on Gaussian distributions is discussed to construct a cost function for efficient rate allocation. Additionally, a rate-distortion efficient video coding scheme is developed that takes advantage of motion-compensated orthogonal transforms. The scheme combines multiple types of motion-compensated orthogonal transforms, variable block sizes, and half-pel accurate motion compensation. The experimental results show that this adaptive scheme outperforms individual motion-compensated orthogonal transforms by up to 2 dB.

1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf