OpenRaiser/Intern-Atlas huggingface dataset:
Real-Time License Plate Recognition on an Embedded DSP-Platform
Authors: Clemens Arth, Florian Limberger, Horst Bischof
Venue: CVPR
Year: 2007

In this paper we present a full-featured license plate detection and recognition system. The system is implemented on an embedded DSP platform and processes a video stream in real-time. It consists of a detection and a character recognition module. The detector is based on the AdaBoost approach presented by Viola and Jones. Detected license plates are segmented into individual characters by using a region-based approach. Character classification is performed with support vector classification. In order to speed up the detection process on the embedded device, a Kalman tracker is integrated into the system. The search area of the detector is limited to locations where the next location of a license plate is predicted. Furthermore, classification results of subsequent frames are combined to improve the class accuracy. The major advantages of our system are its real-time capability and that it does not require any additional sensor input (e.g. from infrared sensors) except a video stream. We evaluate our system on a large number of vehicles and license plates using bad quality video and show that the low resolution can be partly compensated by combining classification results of subsequent frames.
Robust Local Features and their Application in Self-Calibration and Object Recognition on Embedded Systems
Authors: Clemens Arth, Christian Leistner, Horst Bischof
Venue: CVPR
Year: 2007

In recent years many powerful computer vision algorithms have been invented, making automatic or semiautomatic solutions to many popular vision tasks, such as visual object recognition or camera calibration, possible. On the other hand embedded vision platforms and solutions such as smart cameras have successfully emerged, however, only offering limited computational and memory resources. The first contribution of this paper is the investigation of a set of robust local feature detectors and descriptors for application on embedded systems. We briefly describe the methods involved, i.e. the DoG (difference of Gaussian) and MSER (maximally stable extremal regions) detector as well as the PCA-SIFT descriptor, and discuss their suitability for smart systems and their qualification for given tasks. The second contribution of this work is the experimental evaluation of these methods on two challenging tasks, namely fully embedded object recognition on a moderate size database and on the task of robust camera calibration. Our approach is fortified by encouraging results we present at length.
Shadow Removal in Front Projection Environments Using Object Tracking
Authors: Samuel Audet, Jeremy R. Cooperstock
Venue: CVPR
Year: 2007

When an occluding object, such as a person, stands between a projector and a display surface, a shadow results. We can compensate by positioning multiple projectors so they produce identical and overlapping images and by using a system to locate shadows. Existing systems work by detecting either the shadows or the occluders. Shadow detection methods cannot remove shadows before they appear and are sensitive to video projection, while current occluder detection methods require near infrared cameras and illumination. Instead, we propose using a camera-based object tracker to locate the occluder and an algorithm to model the shadows. The algorithm can adapt to other tracking technologies as well. Despite imprecision in the calibration and tracking process, we found that our system performs effective shadow removal with sufficiently low processing delay for interactive applications with video projection.
Variable Bandwidth Image Denoising Using Image-based Noise Models
Authors: Noura Azzabou, Nikos Paragios, Frédéric Guichard, Frédéric Cao
Venue: CVPR
Year: 2007

This paper introduces a variational formulation for image denoising based on a quadratic function over kernels of variable bandwidth. These kernels are scale adaptive and reflect spatial and photometric similarities between pixels. The bandwidth of the kernels is observation-dependent towards improving the accuracy of the reconstruction process and is constrained to be locally smooth. We analyze the evolution of the noise model form the RAW space to the RGB one, by propagating it over the image formation process. The experimental results demonstrate that the use of a variable bandwidth approach and an image intensity dependent noise variance ensures better restoration quality.
Topology-preserving Geometric Deformable Model on Adaptive Quadtree Grid
Authors: Ying Bai, Xiao Han 0007, Jerry L. Prince
Venue: CVPR
Year: 2007

Topology-preserving geometric deformable models (TGDMs) are used to segment objects that have a known topology. Their accuracy is inherently limited, however, by the resolution of the underlying computational grid. Although this can be overcome by using fine-resolution grids, both the computational cost and the size of the resulting contour increase dramatically. In order to maintain computational efficiency and to keep the contour size manageable, we have developed a new framework, termed QTGDMs, for topology-preserving geometric deformable models on balanced quadtree grids (BQGs). In order to do this, definitions and concepts from digital topology on regular grids were extended to BQGs so that characterization of simple points could be made. Other issues critical to the implementation of geometric deformable models are also addressed and a strategy for adapting a BQG during contour evolution is presented. We demonstrate the performance of the QTGDM method using both mathematical phantoms and real medical images.
Biased Manifold Embedding: A Framework for Person-Independent Head Pose Estimation
Authors: Vineeth Nallure Balasubramanian, Jieping Ye, Sethuraman Panchanathan
Venue: CVPR
Year: 2007

The estimation of head pose angle from face images is an integral component of face recognition systems, human computer interfaces and other human-centered computing applications. To determine the head pose, face images with varying pose angles can be considered to be lying on a smooth low-dimensional manifold in high-dimensional feature space. While manifold learning techniques capture the geometrical relationship between data points in the high-dimensional image feature space, the pose label information of the training data samples are neglected in the computation of these embeddings. In this paper, we propose a novel supervised approach to manifold-based non-linear dimensionality reduction for head pose estimation. The Biased Manifold Embedding (BME) framework is pivoted on the ideology of using the pose angle information of the face images to compute a biased neighborhood of each point in the feature space, before determining the low-dimensional embedding. The proposed BME approach is formulated as an extensible framework, and validated with the Isomap, Locally Linear Embedding (LLE) and Laplacian Eigen-maps techniques. A Generalized Regression Neural Network (GRNN) is used to learn the non-linear mapping, and linear multi-variate regression is finally applied on the low-dimensional space to obtain the pose angle. We tested this approach on face images of 24 individuals with pose angles varying from -90deg to +90deg with a granularity of 2. The results showed substantial reduction in the error of pose angle estimation, and robustness to variations in feature spaces, dimensionality of embedding and other parameters.
Hierarchical Learning of Curves Application to Guidewire Localization in Fluoroscopy
Authors: Adrian Barbu, Vassilis Athitsos, Bogdan Georgescu, Stefan Böhm, Peter Durlak, Dorin Comaniciu
Venue: CVPR
Year: 2007

In this paper we present a method for learning a curve model for detection and segmentation by closely integrating a hierarchical curve representation using generative and discriminative models with a hierarchical inference algorithm. We apply this method to the problem of automatic localization of the guidewire in fluoroscopic sequences. In fluoroscopic sequences, the guidewire appears as a hardly visible, non-rigid one-dimensional curve. Our paper has three main contributions. Firstly, we present a novel method to learn the complex shape and appearance of a free-form curve using a hierarchical model of curves of increasing degrees of complexity and a database of manual annotations. Secondly, we present a novel computational paradigm in the context of Marginal Space Learning, in which the algorithm is closely integrated with the hierarchical representation to obtain fast parameter inference. Thirdly, to our knowledge this is the first full system which robustly localizes the whole guidewire and has extensive validation on hundreds of frames. We present very good quantitative and qualitative results on real fluoroscopic video sequences, obtained in just one second per frame.
Reducing correspondence ambiguity in loosely labeled training data
Authors: Kobus Barnard, Quanfu Fan
Venue: CVPR
Year: 2007

We develop an approach to reduce correspondence ambiguity in training data where data items are associated with sets of plausible labels. Our domain is images annotated with keywords where it is not known which part of the image a keyword refers to. In contrast to earlier approaches that build predictive models or classifiers despite the ambiguity, we argue that that it is better to first address the correspondence ambiguity, and then build more complex models from the improved training data. This addresses difficulties of fitting complex models in the face of ambiguity while exploiting all the constraints available from the training data. We contribute a simple and flexible formulation of the problem, and show results validated by a recently developed comprehensive evaluation data set and corresponding evaluation methodology.
3D Pose Estimation Based on Multiple Monocular Cues
Authors: Björn Barrois, Christian Wöhler
Venue: CVPR
Year: 2007

In this study we propose an integrated approach to the problem of 3D pose estimation. The main difference to the majority of known methods is the usage of complementary image information, including intensity and polarisation state of the light reflected from the object surface, edge information, and absolute depth values obtained based on a depth from defocus approach. Our method is based on the comparison of the input image to synthetic images generated by an OpenGL-based renderer using model information about the object provided by CAD data. This comparison provides an error term which is minimised by an iterative optimisation algorithm. Although all six degrees of freedom are estimated, our method requires only a monocular camera, circumventing disadvantages of multiocular camera systems such as the need for external camera calibration. Our framework is open for the inclusion of independently acquired depth data. We evaluate our method on a toy example as well as in two realistic scenarios in the domain of industrial quality inspection. Our experiments regarding complex real-world objects located at a distance of about 0.5 m to the camera show that the algorithm achieves typical accuracies of better than 1 degree for the rotation angles, 1-2 image pixels for the lateral translations, and several millimetres or about 1 percent for the object distance.
Harmony in Motion
Authors: Zohar Barzelay, Yoav Y. Schechner
Venue: CVPR
Year: 2007

Cross-modal analysis offers information beyond that extracted from individual modalities. Consider a camcorder having a single microphone in a cocktail-party: it captures several moving visual objects which emit sounds. A task for audio-visual analysis is to identify the number of independent audio-associated visual objects (AVOs), pinpoint the AVOs' spatial locations in the video and isolate each corresponding audio component. Part of these problems were considered by prior studies, which were limited to simple cases, e.g., a single AVO or stationary sounds. We describe an approach that seeks to overcome these challenges. It acknowledges the importance of temporal features that are based on significant changes in each modality. A probabilistic formalism identifies temporal coincidences between these features, yielding cross-modal association and visual localization. This association is of particular benefit in harmonic sounds, as it enables subsequent isolation of each audio source. We demonstrate this in challenging experiments, having multiple, simultaneous highly nonstationary AVOs.
Performance Benchmark of DSP and FPGA Implementations of Low-Level Vision Algorithms
Authors: Daniel Baumgartner, Peter Rössler, Wilfried Kubinger
Venue: CVPR
Year: 2007

Selecting an embedded hardware platform for image processing has a big influence on the achievable performance. This paper reports our work on a performance benchmark of different implementations of some low-level vision algorithms. The algorithms are implemented on both Digital Signal Processor (DSP) and Field Programmable Gate Array (FPGA) high-speed embedded platforms. The target platforms are a TITMS320C6414 DSP and an Altera Stratix FPGA. The implementations are evaluated, compared and discussed. The DSP implementations outperform the FPGA implementations, but at the cost of spending all its resources to these tasks. FPGAs, however, are well suited to algorithms, which benefit from parallel execution.
Automatic Person Detection and Tracking using Fuzzy Controlled Active Cameras
Authors: Keni Bernardin, Florian van de Camp, Rainer Stiefelhagen
Venue: CVPR
Year: 2007

This paper presents an automatic system for the monitoring of indoor environments using pan-tilt-zoomable cameras. A combination of Haar-feature classifier-based detection and color histogram filtering is used to achieve reliable initialization of person tracks even in the presence of camera movement. A combination of adaptive color and KLT feature trackers for face and upper body allows for robust tracking and track recovery in the presence of occlusion or interference. The continuous recomputation of camera parameters, coupled with a fuzzy controlling scheme allow for smooth tracking of moving targets as well as acquisition of stable facial close ups, similar to the natural behavior of a human cameraman. The system is tested on a series of natural indoor monitoring scenarios and shows a high degree of naturalness, flexibility and robustness.
Geometric Modeling and Calibration of Planar Multi-Projector Displays Using Rational Bezier Patches
Authors: Ezekiel S. Bhasker, Aditi Majumder
Venue: CVPR
Year: 2007

In order to achieve seamless imagery in a planar multi-projector display, geometric distortions and misalignment of images within and across projectors have to be removed. Camera-based calibration methods are popular for achieving this in an automated fashion. Previous methods for geometric calibration fall into two categories: (a) methods that model the geometric function relating the projectors to cameras using simple linear models, like homography, to calibrate the display. These models assume perfect linear devices and cannot address projector nonlinearities, like lens distortions, which are common in most commodity projectors, (b) methods that use piecewise linear approximations to model the relationship between projectors and cameras. These require a dense sampling of the function space to achieve good calibration. In this paper, we present a new closed-form model that relates projectors to cameras in planar multi-projector displays, using rational Bezier patches. This model overcomes the shortcomings of the previous methods by allowing for projectors with significant lens distortion. It can be further used to develop an efficient and accurate geometric calibration method with a sparse sampling of the function.
A Novel Approach to Improve Biometric Recognition Using Rank Level Fusion
Authors: Jay R. Bhatnagar, Ajay Kumar 0001, Nipun Saggar
Venue: CVPR
Year: 2007

This paper proposes a novel approach for rank level fusion which gives improved performance gain verified by experimental results. In the absence of ranked features and instead of using the entire template, we propose using K partitions of the template. The approach proposed in the paper is useful for generating sequential ranks and survivor lists on partitions of template to boost confidence levels by incorporating information from partitions. The proposed algorithm iteratively generates ranks for each partition of the user template. Ranks from template partitions are consolidated to estimate the fusion rank for the classification. This paper investigates rank level fusion for palmprint biometric using two approaches: (1) fixed threshold and resulting survivor list, and (2) iterative thresholds and iteratively refined survivor list. The above approaches achieve similar performances as related manifestations of fusion architecture. The experimental results support the proposition of high in-template similarity of palmprint for a user and its relevance to the intra-modal fusion framework. Experimental results using proposed approach on real palmprint data from 100 users show superior performance with recognition accuracy of 99 % as compared to recognition accuracy of 95% achieved with the conventional approach.
Multiple Instance Learning of Pulmonary Embolism Detection with Geodesic Distance along Vascular Structure
Authors: Jinbo Bi, Jianming Liang
Venue: CVPR
Year: 2007

We propose a novel classification approach for automatically detecting pulmonary embolism (PE) from computed-tomography-angiography images. Unlike most existing approaches that require vessel segmentation to restrict the search space for PEs, our toboggan-based candidate generator is capable of searching the entire lung for any suspicious regions quickly and efficiently. We then exploit the spatial information supplied in the vascular structure as a post-candidate-generation step by designing classifiers with geodesic distances between candidates along the vascular tree. Moreover, a PE represents a cluster of voxels in an image, and thus multiple candidates can be associated with a single PE and the PE is identified if any of its candidates is correctly classified. The proposed algorithm also provides an efficient solution to the problem of learning with multiple positive instances. Our clinical studies with 177 clinical cases demonstrate that the proposed approach outperforms existing detection methods, achieving 81 % sensitivity on an independent test set at 4 false positives per study.
On the Blind Classification of Time Series
Authors: Alessandro Bissacco, Stefano Soatto
Venue: CVPR
Year: 2007

We propose a cord distance in the space of dynamical models that takes into account their dynamics, including transients, output maps and input distributions. In data analysis applications, as opposed to control, the input is often not known and is inferred as part of the (blind) identification. So it is an integral part of the model that should be considered when comparing different time series. Previous work on kernel distances between dynamical models assumed either identical or independent inputs. We extend it to arbitrary distributions, highlighting connections with system identification, independent component analysis, and optimal transport. The increased modeling power is demonstrated empirically on gait classification from simple visual features.
Fast Human Pose Estimation using Appearance and Motion via Multi-Dimensional Boosting Regression
Authors: Alessandro Bissacco, Ming-Hsuan Yang 0001, Stefano Soatto
Venue: CVPR
Year: 2007

We address the problem of estimating human pose in video sequences, where rough location has been determined. We exploit both appearance and motion information by defining suitable features of an image and its temporal neighbors, and learning a regression map to the parameters of a model of the human body using boosting techniques. Our algorithm can be viewed as a fast initialization step for human body trackers, or as a tracker itself. We extend gradient boosting techniques to learn a multi-dimensional map from (rotated and scaled) Haar features to the entire set of joint angles representing the full body pose. We test our approach by learning a map from image patches to body joint angles from synchronized video and motion capture walking data. We show how our technique enables learning an efficient real-time pose estimator, validated on publicly available datasets.
Efficient Indexing For Articulation Invariant Shape Matching And Retrieval
Authors: Soma Biswas, Gaurav Aggarwal, Rama Chellappa
Venue: CVPR
Year: 2007

Most shape matching methods are either fast but too simplistic to give the desired performance or promising as far as performance is concerned but computationally demanding. In this paper, we present a very simple and efficient approach that not only performs almost as good as many state-of-the-art techniques but also scales up to large databases. In the proposed approach, each shape is indexed based on a variety of simple and easily computable features which are invariant to articulations and rigid transformations. The features characterize pairwise geometric relationships between interest points on the shape, thereby providing robustness to the approach. Shapes are retrieved using an efficient scheme which does not involve costly operations like shape-wise alignment or establishing correspondences. Even for a moderate size database of 1000 shapes, the retrieval process is several times faster than most techniques with similar performance. Extensive experimental results are presented to illustrate the advantages of our approach as compared to the best in the field.
On Constant Focal Length Self-Calibration From Multiple Views
Authors: Benoît Bocquillon, Adrien Bartoli, Pierre Gurdjos, Alain Crouzil
Venue: CVPR
Year: 2007

We investigate the problem of finding the metric structure of a general 3D scene viewed by a moving camera with square pixels and constant unknown focal length. While the problem has a concise and well-understood formulation in the stratified framework thanks to the absolute dual quadric, two open issues remain. The first issue concerns the generic Critical Motion Sequences, i.e. camera motions for which self-calibration is ambiguous. Most of the previous work focuses on the varying focal length case. We provide a thorough study of the constant focal length case. The second issue is to solve the nonlinear set of equations in four unknowns arising from the dual quadric formulation. Most of the previous work either does local nonlinear optimization, thereby requiring an initial solution, or linearizes the problem, which introduces artificial degeneracies, most of which likely to arise in practice. We use interval analysis to solve this problem. The resulting algorithm is guaranteed to find the solution and is not subject to artificial degeneracies. Directly using interval analysis usually results in computationally expensive algorithms. We propose a carefully chosen set of inclusion functions, making it possible to find the solution within few seconds. Comparisons of the proposed algorithm with existing ones are reported for simulated and real data.