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Author

Stefan Uhlmann

Bio: Stefan Uhlmann is an academic researcher from Tampere University of Technology. The author has contributed to research in topics: Contextual image classification & Synthetic aperture radar. The author has an hindex of 8, co-authored 22 publications receiving 291 citations.

Papers
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Journal ArticleDOI
TL;DR: The classification results show that the additional color features introduce a new level of discrimination and provide noteworthy improvement in classification performance (compared with the traditionally employed PolSAR and texture features) within the application of land use and land cover classification.
Abstract: Polarimetric synthetic aperture radar (PolSAR) data are used extensively for terrain classification applying SAR features from various target decompositions and certain textural features. However, one source of information has so far been neglected from PolSAR classification: Color. It is a common practice to visualize PolSAR data by color coding methods and thus, it is possible to extract powerful color features from such pseudocolor images so as to provide additional data for a superior terrain classification. In this paper, we first review previous attempts for PolSAR classifications using various feature combinations and then we introduce and perform in-depth investigation of the application of color features over the Pauli color-coded images besides SAR and texture features. We run an extensive set of comparative evaluations using 24 different feature set combinations over three images of the Flevoland- and the San Francisco Bay region from the RADARSAT-2 and the AIRSAR systems operating in C- and L-bands, respectively. We then consider support vector machines and random forests classifier topologies to test and evaluate the role of color features over the classification performance. The classification results show that the additional color features introduce a new level of discrimination and provide noteworthy improvement in classification performance (compared with the traditionally employed PolSAR and texture features) within the application of land use and land cover classification.

142 citations

Journal ArticleDOI
TL;DR: This work extracts domain knowledge about sport events recorded by multiple users, by classifying the sport type into soccer, American football, basketball, tennis, ice-hockey, or volleyball, by using a multi-user and multimodal approach.
Abstract: The recent proliferation of mobile video content has emphasized the need for applications such as automatic organization and automatic editing of videos. These applications could greatly benefit from domain knowledge about the content. However, extracting semantic information from mobile videos is a challenging task, due to their unconstrained nature. We extract domain knowledge about sport events recorded by multiple users, by classifying the sport type into soccer, American football, basketball, tennis, ice-hockey, or volleyball. We adopt a multi-user and multimodal approach, where each user simultaneously captures audio-visual content and auxiliary sensor data (from magnetometers and accelerometers). Firstly, each modality is separately analyzed; then, analysis results are fused for obtaining the sport type. The auxiliary sensor data is used for extracting more discriminative spatio-temporal visual features and efficient camera motion features. The contribution of each modality to the fusion process is adapted according to the quality of the input data. We performed extensive experiments on data collected at public sport events, showing the merits of using different combinations of modalities and fusion methods. The results indicate that analyzing multimodal and multi-user data, coupled with adaptive fusion, improves classification accuracies in most tested cases, up to 95.45%.

31 citations

Journal ArticleDOI
TL;DR: An extensive set of experiments show that individual visual features or their combination with traditional SAR features introduce a new level of discrimination and provide noteworthy improvement of classification accuracies within the application of land use and land cover classification for dual- and single-pol image data.
Abstract: Fully and partially polarimetric SAR data in combination with textural features have been used extensively for terrain classification. However, there is another type of visual feature that has so far been neglected from polarimetric SAR classification: Color. It is a common practice to visualize polarimetric SAR data by color coding methods and thus it is possible to extract powerful color features from such pseudo color images so as to gather additional crucial information for an improved terrain classification. In this paper, we investigate the application of several individual visual features over different pseudo color generated images along with the traditional SAR and texture features for a novel supervised classification application of dual- and single-polarized SAR data. We then draw the focus on evaluating the effects of the applied pseudo coloring methods on the classification performance. An extensive set of experiments show that individual visual features or their combination with traditional SAR features introduce a new level of discrimination and provide noteworthy improvement of classification accuracies within the application of land use and land cover classification for dual- and single-pol image data.

25 citations

Proceedings ArticleDOI
07 Oct 2008
TL;DR: An overview of related factors, which are to be considered in a portable personality environment, and the current state-of-the-art of profile acquisition and management algorithms to obtain and handle personalized information.
Abstract: With the advances in ubiquitous computing, there is an increasing focus on personalization of user information especially in web applications. Currently those personalized user profiles are scattered around the Internet, mostly stored for each individual website. Therefore, this prohibits the usage of those profiles in other environments such as shopping in local stores or sharing interests among people. The so-called Portable Personality focuses on the management and distribution of personalized profiles via mobile devices. This paper provides an overview of related factors, which are to be considered in a portable personality environment. We discuss common user profile categorization approaches and their possible representation. Moreover, we mention the current state-of-the-art of profile acquisition and management algorithms to obtain and handle personalized information. This also includes approaches towards portable profiles. At the end, profile merging and personalization algorithms are covered to handle the challenges of aggregate multiple profiles and personalized recommendations based on distributed (portable) profiles.

22 citations

Journal ArticleDOI
01 Aug 2012
TL;DR: Both visual and numerical performance evaluations of the proposed framework over two benchmark SAR images demonstrate its superiority and a significant performance gap against several major classifiers in this field.
Abstract: Terrain classification over polarimetric synthetic aperture radar (SAR) images has been an active research field where several features and classifiers have been proposed up to date. However, some key questions, e.g., 1) how to select certain features so as to achieve highest discrimination over certain classes?, 2) how to combine them in the most effective way?, 3) which distance metric to apply?, 4) how to find the optimal classifier configuration for the classification problem in hand?, 5) how to scale/adapt the classifier if large number of classes/features are present?, and finally, 6) how to train the classifier efficiently to maximize the classification accuracy?, still remain unanswered. In this paper, we propose a collective network of (evolutionary) binary classifier (CNBC) framework to address all these problems and to achieve high classification performance. The CNBC framework adapts a “Divide and Conquer” type approach by allocating several NBCs to discriminate each class and performs evolutionary search to find the optimal BC in each NBC. In such an (incremental) evolution session, the CNBC body can further dynamically adapt itself with each new incoming class/feature set without a full-scale retraining or reconfiguration. Both visual and numerical performance evaluations of the proposed framework over two benchmark SAR images demonstrate its superiority and a significant performance gap against several major classifiers in this field.

21 citations


Cited by
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Journal ArticleDOI
TL;DR: This review has revealed that RF classifier can successfully handle high data dimensionality and multicolinearity, being both fast and insensitive to overfitting.
Abstract: A random forest (RF) classifier is an ensemble classifier that produces multiple decision trees, using a randomly selected subset of training samples and variables. This classifier has become popular within the remote sensing community due to the accuracy of its classifications. The overall objective of this work was to review the utilization of RF classifier in remote sensing. This review has revealed that RF classifier can successfully handle high data dimensionality and multicolinearity, being both fast and insensitive to overfitting. It is, however, sensitive to the sampling design. The variable importance (VI) measurement provided by the RF classifier has been extensively exploited in different scenarios, for example to reduce the number of dimensions of hyperspectral data, to identify the most relevant multisource remote sensing and geographic data, and to select the most suitable season to classify particular target classes. Further investigations are required into less commonly exploited uses of this classifier, such as for sample proximity analysis to detect and remove outliers in the training samples.

3,244 citations

Journal ArticleDOI
TL;DR: Experimental results with three Radarsat-2 images in quad polarization mode indicate that classification accuracies could be significantly increased by integrating spatial and polarimetric features using ensemble learning strategies.
Abstract: Fully Polarimetric Synthetic Aperture Radar (PolSAR) has the advantages of all-weather, day and night observation and high resolution capabilities. The collected data are usually sorted in Sinclair matrix, coherence or covariance matrices which are directly related to physical properties of natural media and backscattering mechanism. Additional information related to the nature of scattering medium can be exploited through polarimetric decomposition theorems. Accordingly, PolSAR image classification gains increasing attentions from remote sensing communities in recent years. However, the above polarimetric measurements or parameters cannot provide sufficient information for accurate PolSAR image classification in some scenarios, e.g. in complex urban areas where different scattering mediums may exhibit similar PolSAR response due to couples of unavoidable reasons. Inspired by the complementarity between spectral and spatial features bringing remarkable improvements in optical image classification, the complementary information between polarimetric and spatial features may also contribute to PolSAR image classification. Therefore, the roles of textural features such as contrast, dissimilarity, homogeneity and local range, morphological profiles (MPs) in PolSAR image classification are investigated using two advanced ensemble learning (EL) classifiers: Random Forest and Rotation Forest. Supervised Wishart classifier and support vector machines (SVMs) are used as benchmark classifiers for the evaluation and comparison purposes. Experimental results with three Radarsat-2 images in quad polarization mode indicate that classification accuracies could be significantly increased by integrating spatial and polarimetric features using ensemble learning strategies. Rotation Forest can get better accuracy than SVM and Random Forest, in the meantime, Random Forest is much faster than Rotation Forest.

340 citations

Journal ArticleDOI
TL;DR: This paper focuses on the video content analysis techniques applied in sportscasts over the past decade from the perspectives of fundamentals and general review, a content hierarchical model, and trends and challenges.
Abstract: Sports data analysis is becoming increasingly large scale, diversified, and shared, but difficulty persists in rapidly accessing the most crucial information. Previous surveys have focused on the methodologies of sports video analysis from the spatiotemporal viewpoint instead of a content-based viewpoint, and few of these studies have considered semantics. This paper develops a deeper interpretation of content-aware sports video analysis by examining the insight offered by research into the structure of content under different scenarios. On the basis of this insight, we provide an overview of the themes particularly relevant to the research on content-aware systems for broadcast sports. Specifically, we focus on the video content analysis techniques applied in sportscasts over the past decade from the perspectives of fundamentals and general review, a content hierarchical model, and trends and challenges. Content-aware analysis methods are discussed with respect to object-, event-, and context-oriented groups. In each group, the gap between sensation and content excitement must be bridged using proper strategies. In this regard, a content-aware approach is required to determine user demands. Finally, this paper summarizes the future trends and challenges for sports video analysis. We believe that our findings can advance the field of research on content-aware video analysis for broadcast sports.

179 citations

Journal ArticleDOI
TL;DR: Making full use of the prior knowledge of POL-SAR data and local spatial information, the proposed method overcomes shortcomings of traditional methods, in which they are sensitive to extracted features and slow to execute.
Abstract: Inspired by a popular deep neural network, i.e., deep belief network (DBN), a novel method for polarimetric synthetic aperture radar (POL-SAR) image classification is proposed in this paper. For the particularity of POL-SAR data, a new type of restricted Boltzmann machine (RBM) is specially defined, which we name the Wishart–Bernoulli RBM (WBRBM), and is used to form a deep network named as Wishart DBN (W-DBN). Numerous unlabeled POL-SAR pixels are made full use of in the modeling of POL-SAR pixels by W-DBN. In addition, the coherency matrix is used directly to represent a POL-SAR pixel without any manual feature extraction, which is simple and time saving. Local spatial information, together with the confusion matrix, is used in this paper to clean the preliminary classification result obtained by the method based on W-DBN. Making full use of the prior knowledge of POL-SAR data and local spatial information, the proposed method overcomes shortcomings of traditional methods, in which they are sensitive to extracted features and slow to execute. The experiments, tested on three POL-SAR data sets, show that the proposed method produces better results and is much faster than traditional methods.

142 citations

Journal ArticleDOI
TL;DR: The term serious storytelling is introduced as a new potential media genre – defining serious storytelling as storytelling with a purpose beyond entertainment – and several application areas are predicted, including wellbeing and health, medicine, psychology, education and online communication.
Abstract: In human culture, storytelling is a long-established tradition. The reasons people tell stories are manifold: to entertain, to transfer knowledge between generations, to maintain cultural heritage, or to warn others of dangers. With the emergence of the digitisation of media, many new possibilities to tell stories in serious and non-entertainment contexts emerged. A very simple example is the idea of serious gaming, as in, digital games without the primary purpose of entertainment. In this paper, we introduce the term serious storytelling as a new potential media genre --- defining serious storytelling as storytelling with a purpose beyond entertainment. We also put forward a review of existing potential application areas, and develop a framework for serious storytelling. We foresee several application areas for this fundamental concept, including wellbeing and health, medicine, psychology, education, ethical problem solving, e-leadership and management, qualitative journalism, serious digital games, simulations and virtual training, user experience studies, and online communication.

127 citations