Transformées basées graphes pour la compression de nouvelles modalités d’image

Due to the large availability of new camera types capturing extra geometrical information, as well as the emergence of new image modalities such as light fields and omni-directional images, a huge amount of high dimensional data has to be stored and delivered. The ever growing streaming and storage requirements of these new image modalities require novel image coding tools that exploit the complex structure of those data. This thesis aims at exploring novel graph based approaches for adapting traditional image transform coding techniques to the emerging data types where the sampled information are lying on irregular structures. In a first contribution, novel local graph based transforms are designed for light field compact representations. By leveraging a careful design of local transform supports and a local basis functions optimization procedure, significant improvements in terms of energy compaction can be obtained. Nevertheless, the locality of the supports did not permit to exploit long term dependencies of the signal. This led to a second contribution where different sampling strategies are investigated. Coupled with novel prediction methods, they led to very prominent results for quasi-lossless compression of light fields. The third part of the thesis focuses on the definition of rate-distortion optimized sub-graphs for the coding of omni-directional content. If we move further and give more degree of freedom to the graphs we wish to use, we can learn or define a model (set of weights on the edges) that might not be entirely reliable for transform design. The last part of the thesis is dedicated to theoretically analyze the effect of the uncertainty on the efficiency of the graph transforms.En raison de la grande disponibilité de nouveaux types de caméras capturant des informations géométriques supplémentaires, ainsi que de l'émergence de nouvelles modalités d'image telles que les champs de lumière et les images omnidirectionnelles, il est nécessaire de stocker et de diffuser une quantité énorme de hautes dimensions. Les exigences croissantes en matière de streaming et de stockage de ces nouvelles modalités d’image nécessitent de nouveaux outils de codage d’images exploitant la structure complexe de ces données. Cette thèse a pour but d'explorer de nouvelles approches basées sur les graphes pour adapter les techniques de codage de transformées d'image aux types de données émergents où les informations échantillonnées reposent sur des structures irrégulières. Dans une première contribution, de nouvelles transformées basées sur des graphes locaux sont conçues pour des représentations compactes des champs de lumière. En tirant parti d’une conception minutieuse des supports de transformées locaux et d’une procédure d’optimisation locale des fonctions de base , il est possible d’améliorer considérablement le compaction d'énergie. Néanmoins, la localisation des supports ne permettait pas d'exploiter les dépendances à long terme du signal. Cela a conduit à une deuxième contribution où différentes stratégies d'échantillonnage sont étudiées. Couplés à de nouvelles méthodes de prédiction, ils ont conduit à des résultats très importants en ce qui concerne la compression quasi sans perte de champs de lumière statiques. La troisième partie de la thèse porte sur la définition de sous-graphes optimisés en distorsion de débit pour le codage de contenu omnidirectionnel. Si nous allons plus loin et donnons plus de liberté aux graphes que nous souhaitons utiliser, nous pouvons apprendre ou définir un modèle (ensemble de poids sur les arêtes) qui pourrait ne pas être entièrement fiable pour la conception de transformées. La dernière partie de la thèse est consacrée à l'analyse théorique de l'effet de l'incertitude sur l'efficacité des transformées basées graphes

Prediction and Sampling with Local Graph Transforms for Quasi-Lossless Light Field Compression

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Rate-Distortion Optimized Super-Ray Merging for Light Field Compression

International audienceIn this paper, we focus on the problem of compressing dense light fields which represent very large volumes of highly redundant data. In our scheme, view synthesis based on convolutional neural networks (CNN) is used as a first prediction step to exploit interview correlation. Super-rays are then constructed to capture the interview and spatial redundancy remaining in the prediction residues. To ensure that the super-ray segmentation is highly correlated with the residues to be encoded, the super-rays are computed on synthesized residues (the difference between the four transmitted corner views and their corresponding synthesized views), instead of the synthesized views. Neighboring super-rays are merged into a larger super-ray according to a rate-distortion cost. A 4D shape adaptive discrete cosine transform (SA-DCT) is applied per super-ray on the prediction residues in both the spatial and angular dimensions. A traditional coding scheme consisting of quantization and entropy coding is then used for encoding the transformed coefficients. Experimental results show that the proposed coding scheme outperforms HEVC-based schemes at low bitrate

Graph-based multimodal multi-lesion DLBCL treatment response prediction from PET images

Diffuse Large B-cell Lymphoma (DLBCL) is a lymphatic cancer involving one or more lymph nodes and extranodal sites. Its diagnostic and follow-up rely on Positron Emission Tomography (PET) and Computed Tomography (CT). After diagnosis, the number of nonresponding patients to standard front-line therapy remains significant (30-40%). This work aims to develop a computer-aided approach to identify high-risk patients requiring adapted treatment by efficiently exploiting all the information available for each patient, including both clinical and image data. We propose a method based on recent graph neural networks that combine imaging information from multiple lesions, and a cross-attention module to integrate different data modalities efficiently. The model is trained and evaluated on a private prospective multicentric dataset of 583 patients. Experimental results show that our proposed method outperforms classical supervised methods based on either clinical, imaging or both clinical and imaging data for the 2-year progression-free survival (PFS) classification accuracy

Transformées basées graphes pour la compression de nouvelles modalités d’image

Due to the large availability of new camera types capturing extra geometrical information, as well as the emergence of new image modalities such as light fields and omni-directional images, a huge amount of high dimensional data has to be stored and delivered. The ever growing streaming and storage requirements of these new image modalities require novel image coding tools that exploit the complex structure of those data. This thesis aims at exploring novel graph based approaches for adapting traditional image transform coding techniques to the emerging data types where the sampled information are lying on irregular structures. In a first contribution, novel local graph based transforms are designed for light field compact representations. By leveraging a careful design of local transform supports and a local basis functions optimization procedure, significant improvements in terms of energy compaction can be obtained. Nevertheless, the locality of the supports did not permit to exploit long term dependencies of the signal. This led to a second contribution where different sampling strategies are investigated. Coupled with novel prediction methods, they led to very prominent results for quasi-lossless compression of light fields. The third part of the thesis focuses on the definition of rate-distortion optimized sub-graphs for the coding of omni-directional content. If we move further and give more degree of freedom to the graphs we wish to use, we can learn or define a model (set of weights on the edges) that might not be entirely reliable for transform design. The last part of the thesis is dedicated to theoretically analyze the effect of the uncertainty on the efficiency of the graph transforms.En raison de la grande disponibilité de nouveaux types de caméras capturant des informations géométriques supplémentaires, ainsi que de l'émergence de nouvelles modalités d'image telles que les champs de lumière et les images omnidirectionnelles, il est nécessaire de stocker et de diffuser une quantité énorme de hautes dimensions. Les exigences croissantes en matière de streaming et de stockage de ces nouvelles modalités d’image nécessitent de nouveaux outils de codage d’images exploitant la structure complexe de ces données. Cette thèse a pour but d'explorer de nouvelles approches basées sur les graphes pour adapter les techniques de codage de transformées d'image aux types de données émergents où les informations échantillonnées reposent sur des structures irrégulières. Dans une première contribution, de nouvelles transformées basées sur des graphes locaux sont conçues pour des représentations compactes des champs de lumière. En tirant parti d’une conception minutieuse des supports de transformées locaux et d’une procédure d’optimisation locale des fonctions de base , il est possible d’améliorer considérablement le compaction d'énergie. Néanmoins, la localisation des supports ne permettait pas d'exploiter les dépendances à long terme du signal. Cela a conduit à une deuxième contribution où différentes stratégies d'échantillonnage sont étudiées. Couplés à de nouvelles méthodes de prédiction, ils ont conduit à des résultats très importants en ce qui concerne la compression quasi sans perte de champs de lumière statiques. La troisième partie de la thèse porte sur la définition de sous-graphes optimisés en distorsion de débit pour le codage de contenu omnidirectionnel. Si nous allons plus loin et donnons plus de liberté aux graphes que nous souhaitons utiliser, nous pouvons apprendre ou définir un modèle (ensemble de poids sur les arêtes) qui pourrait ne pas être entièrement fiable pour la conception de transformées. La dernière partie de la thèse est consacrée à l'analyse théorique de l'effet de l'incertitude sur l'efficacité des transformées basées graphes

Rate-Distortion Optimized Graph Coarsening and Partitioning for Light Field Coding

International audienceGraph-based transforms are powerful tools for signal representation and energy compaction. However, their use for high dimensional signals such as light fields poses obvious problems of complexity. To overcome this difficulty, one can consider local graph transforms defined on supports of limited dimension, which may however not allow us to fully exploit long-term signal correlation. In this paper, we present methods to optimize local graph supports in a rate distortion sense for efficient light field compression. A large graph support can be well adapted for compression efficiency, however at the expense of high complexity. In this case, we use graph reduction techniques to make the graph transform feasible. We also consider spectral clustering to reduce the dimension of the graph supports while controlling both rate and complexity. We derive the distortion and rate models which are then used to guide the graph optimization. We describe a complete light field coding scheme based on the proposed graph optimization tools. Experimental results show rate-distortion performance gains compared to the use of fixed graph support. The method also provides competitive results when compared against HEVC-based and the JPEG Pleno light field coding schemes. We also assess the method against a homography-based low rank approximation and a Fourier disparity layer based coding method

Prediction and Sampling with Local Graph Transforms for Quasi-Lossless Light Field Compression

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Graph-based Spatio-angular Prediction for Quasi-Lossless Compression of Light Fields

International audienceGraph-based transforms have been shown to be powerful tools for image compression. However , the computation of the basis functions becomes rapidly untractable when the support increases, i.e. when the dimension of the data is high as in the case of light fields. Local transforms with limited supports have been investigated to cope with this difficulty. Nevertheless , the locality of the support may not allow us to fully exploit long term dependencies in the signal. In this paper, we describe a graph-based prediction solution that allows taking advantage of intra prediction mechanisms as well as of the good energy compaction properties of the graph transform. The approach relies on a separable spatio-angular transform and derives low frequency spatio-angular coefficients from one single compressed reference view and from the high angular frequency coefficients. In the tests, we used HEVC-Intra, with QP=0, to encode the reference frame with high quality. The high angular frequency coefficients containing very little energy are coded using a simple entropy coder. The approach is shown to be very efficient in a context of high quality quasi-lossless compression of light fields

Rate-Distortion Optimized Super-Ray Merging for Light Field Compression

International audienceIn this paper, we focus on the problem of compressing dense light fields which represent very large volumes of highly redundant data. In our scheme, view synthesis based on convolutional neural networks (CNN) is used as a first prediction step to exploit interview correlation. Super-rays are then constructed to capture the interview and spatial redundancy remaining in the prediction residues. To ensure that the super-ray segmentation is highly correlated with the residues to be encoded, the super-rays are computed on synthesized residues (the difference between the four transmitted corner views and their corresponding synthesized views), instead of the synthesized views. Neighboring super-rays are merged into a larger super-ray according to a rate-distortion cost. A 4D shape adaptive discrete cosine transform (SA-DCT) is applied per super-ray on the prediction residues in both the spatial and angular dimensions. A traditional coding scheme consisting of quantization and entropy coding is then used for encoding the transformed coefficients. Experimental results show that the proposed coding scheme outperforms HEVC-based schemes at low bitrate

Unsupervised Multimodal Supervoxel Merging towards Brain Tumor Segmentation

International audienceAutomated brain tumor segmentation is challenging given the tumor's variability in size, shape, and image intensity. This paper focuses on the fusion of multimodal information coming from different Magnetic Resonance (MR) imaging sequences. We argue it is important to exploit all the modality complementarity to better segment and later determine the aggressiveness of tumors. However, simply concatenating the multimodal data as channels of a single image generates a high volume of redundant information. Therefore, we propose a supervoxel-based approach that regroups pixels sharing perceptually similar information across the different modalities to produce a single coherent oversegmentation. To further reduce redundant information while keeping meaningful borders, we include a variance constraint and a supervoxel merging step. Our experimental validation shows that the proposed merging strategy produces high-quality clustering results useful for brain tumor segmentation. Indeed, our method reaches an ASA score of 0.712 compared to 0.316 for the monomodal approach, indicating that the supervoxels accommodate well tumor boundaries. Our approach also improves by 11.5% the Global Score (GS), showing clusters effectively group pixels similar in intensity and texture