194 results for Klette, Reinhard

  • Generalised residual images' effect on illumination artifact removal for correspondence algorithms

    Vaudrey, Tobi; Morales, S; Wedel, A; Klette, Reinhard (2011)

    Journal article
    The University of Auckland Library

    The intensity (grey value) consistency of image pixels in a sequence or stereo camera setup is of central importance to numerous computer vision applications. Most stereo matching and optical flow algorithms minimise an energy function composed of a data term and a regularity or smoothing term. To date, well performing methods rely on the intensity consistency of the image pixel values to model the data term. Such a simple model fails if the illumination is (even slightly) different between the input images. Amongst other situations, this may happen due to background illumination change over the sequence, different reflectivity of a surface, vignetting, or shading effects. In this paper, we investigate the removal of illumination artifacts and show that generalised residual images substantially improve the accuracy of correspondence algorithms. In particular, we motivate the concept of residual images and show two evaluation approaches using either ground truth correspondence fields (for stereo matching and optical flow algorithms) or errors based on a predicted view (for stereo matching algorithms).

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  • Digital planarity-A review

    Brimkov, V; Coeurjolly, D; Klette, Reinhard (2007)

    Journal article
    The University of Auckland Library

    Digital planarity is defined by digitizing Euclidean planes in the three-dimensional digital space of voxels; voxels are given either in the grid-point or the grid-cube model. The paper summarizes results (also including most of the proofs) about different aspects of digital planarity, such as supporting or separating Euclidean planes, characterizations in arithmetic geometry, periodicity, connectivity, and algorithmic solutions. The paper provides a uniform presentation, which further extends and details a recent book chapter in [R. Klette, A. Rosenfeld, Digital Geometry—Geometric Methods for Digital Picture Analysis, Morgan Kaufmann, San Francisco, 2004].

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  • Kalman-filter based spatio-temporal disparity integration

    Morales, S; Klette, Reinhard (2013)

    Journal article
    The University of Auckland Library

    Vision-based applications usually have as input a continuous stream of data. Therefore, it is possible to use the information generated in previous frames to improve the analysis of the current one. In the context of video-based driver-assistance systems, objects present in a scene typically perform a smooth motion through the image sequence. By considering a motion model for the ego-vehicle, it is possible to take advantage of previously processed data when analysing the current frame. This paper presents a Kalman filter-based approach that focuses on the reduction of the uncertainty in depth estimation (via stereo-vision algorithms) by using information from the temporal and spatial domains. For each pixel in the current disparity map, we refine the estimated value using the stereo data from a neighbourhood of pixels in previous and current frames. We aim at an improvement of existing methods that use data from the temporal domain by adding extra information from the spatial domain. To show the effectiveness of the proposed method, we analyse the performance on long synthetic sequences using different stereo matching algorithms, and compare the results obtained by the previous and the suggested approach.

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  • Wide-angle vision for road views

    Huang, F; Fehrs, K; Hartmann, G; Klette, Reinhard (2013-01)

    Journal article
    The University of Auckland Library

    The field-of-view of a wide-angle image is greater than (say) 90 degrees, and so contains more information than available in a standard image. A wide field-of-view is more advantageous than standard input for understanding the geometry of 3D scenes, and for estimating the poses of panoramic sensors within such scenes. Thus, wide-angle imaging sensors and methodologies are commonly used in various road-safety, street surveillance, street virtual touring, or street 3D modelling applications. The paper reviews related wide-angle vision technologies by focusing on mathematical issues rather than on hardware.

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  • Comparison of two 3D tracking paradigms for freely flying insects

    Risse, B; Berh, D; Tao, Junli; Jiang, X; Klette, Reinhard; Klaembt, C (2013-10)

    Journal article
    The University of Auckland Library

    In this paper, we discuss and compare state-of-the-art 3D tracking paradigms for flying insects such as Drosophila melanogaster. If two cameras are employed to estimate the trajectories of these identical appearing objects, calculating stereo and temporal correspondences leads to an NP-hard assignment problem. Currently, there are two different types of approaches discussed in the literature: probabilistic approaches and global correspondence selection approaches. Both have advantages and limitations in terms of accuracy and complexity. Here, we present algorithms for both paradigms. The probabilistic approach utilizes the Kalman filter for temporal tracking. The correspondence selection approach calculates the trajectories based on an overall cost function. Limitations of both approaches are addressed by integrating a third camera to verify consistency of the stereo pairings and to reduce the complexity of the global selection. Furthermore, a novel greedy optimization scheme is introduced for the correspondence selection approach. We compare both paradigms based on synthetic data with ground truth availability. Results show that the global selection is more accurate, while the previously proposed tracking-by-matching (probabilistic) approach is causal and feasible for longer tracking periods and very high target densities. We further demonstrate that our extended global selection scheme outperforms current correspondence selection approaches in tracking accuracy and tracking time.

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  • Corridor detection for vision-based driver assistance systems.

    Jiang, R; Klette, Reinhard; Vaudrey, Tobi; Wang, S (2011)

    Journal article
    The University of Auckland Library

    A significant component of driver assistance systems (DAS) is lane detection, and has been studied since the 1990s. However, improving and generalizing lane detection solutions proved to be a challenging task until recently. A (physical) lane is defined by road boundaries or various kinds of lane marks, and this is only partially applicable for modeling the space an ego-vehicle is able to drive in. This paper proposes a concept of (virtual) corridor for modeling this space. A corridor depends on information available about the motion of the ego-vehicle, as well as about the (physical) lane. This paper also suggests a modified version of Euclidean Distance Transform (EDT), named Row Orientation Distance Transform (RODT), to facilitate the detection of corridor boundary points. Then, boundary selection and road patch extension are applied as post-processing. Moreover, this paper also informs about the possible application of corridor for driver assistance. Finally, experiments using images from highways and urban roads with some challenging road situations are presented, illustrating the effectiveness of the proposed corridor detection algorithm. Comparison of lane and corridor on a public dataset is also provided.

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  • Visual lane analysis and higher-order tasks: a concise review

    Shin, Bok-Suk; Xu, Zezhong; Klette, Reinhard (2014-08)

    Journal article
    The University of Auckland Library

    Lane detection, lane tracking, or lane departure warning have been the earliest components of vision-based driver assistance systems. At first (in the 1990s), they have been designed and implemented for situations defined by good viewing conditions and clear lane markings on highways. Since then, accuracy for particular situations (also for challenging conditions), robustness for a wide range of scenarios, time efficiency, and integration into higher-order tasks define visual lane detection and tracking as a continuing research subject. The paper reviews past and current work in computer vision that aims at real-time lane or road understanding under a comprehensive analysis perspective, for moving on to higher-order tasks combined with various lane analysis components, and introduces related work along four independent axes as shown in Fig. 2. This concise review provides not only summarizing definitions and statements for understanding key ideas in related work, it also presents selected details of potentially applicable methods, and shows applications for illustrating progress. This review helps to plan future research which can benefit from given progress in visual lane analysis. It supports the understanding of newly emerging subjects which combine lane analysis with more complex road or traffic understanding issues. The review should help readers in selecting suitable methods for their own targeted scenario.

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  • Landmark Initialization for Unscented Kalman Filter Sensor Fusion for Monocular Camera Localization

    Hartmann, G; Huang, F; Klette, Reinhard (2013-03)

    Journal article
    The University of Auckland Library

    The determination of the pose of the imaging camera is a fundamental problem in computer vision. In the monocular case, difficulties in determining the scene scale and the limitation to bearing-only measurements increase the difficulty in estimating camera pose accurately. Many mobile phones now contain inertial measurement devices, which may lend some aid to the task of determining camera pose. In this study, by means of simulation and real-world experimentation, we explore an approach to monocular camera localization that incorporates both observations of the environment and measurements from accelerometers and gyroscopes. The unscented Kalman filter was implemented for this task. Our main contribution is a novel approach to landmark initialization in a Kalman filter; we characterize the tolerance to noise that this approach allows.

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  • Novel Backprojection Method for Monocular Head Pose Estimation

    Ju, K; Shin, Bok Suk; Klette, Reinhard (2013-07)

    Journal article
    The University of Auckland Library

    Estimating a driver’s head pose is an important task in driver-assistance systems because it can provide information about where a driver is looking, thereby giving useful cues about the status of the driver (i.e., paying proper attention, fatigued, etc.). This study proposes a system for estimating the head pose using monocular images, which includes a novel use of backprojection. The system can use a single image to estimate a driver’s head pose at a particular time stamp, or an image sequence to support the analysis of a driver’s status. Using our proposed system, we compared two previous pose estimation approaches. We introduced an approach for providing ground-truth reference data using a mannequin model. Our experimental results demonstrate that the proposed system provides relatively accurate estimations of the yaw, tilt, and roll angle. The results also show that one of the pose estimation approaches (perspective-n-point, PnP) provided a consistently better estimate compared to the other (pose from orthography and scaling with iterations, POSIT) using our proposed system.

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  • ADR shape descriptor – Distance between shape centroids versus shape diameter

    Klette, Reinhard; Žunić, Joviša (2012-06)

    Journal article
    The University of Auckland Library

    In this paper we study the ADR shape descriptor ρ(S), where ADR is short for “asymmetries in the distribution of roughness”. This descriptor was defined in 1998 as the ratio of the squared distance between two different shape centroids (namely of area and frontier) to the squared shape diameter. After known for more than ten years, the behavior of ρ(S) was not well understood till today, thus hindering its application. Two very basic questions remained unanswered so far: –What is the range for ρ(S), if S is any bounded compact shape? –How do shapes look like having a large ρ(S) value? This paper answers both questions. We show that ρ(S) ranges over the interval [0, 1). We show that the established upper bound 1 is the best possible by constructing shapes whose ρ(S) values are arbitrary close to 1. In experiments we provide examples to indicate the kind of shapes that have relatively large ρ(S) values.

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  • Generation of Random Digital Simple Curves with Artistic Emulation

    Bhowmick, Partha; Klette, Reinhard (2014-01)

    Journal article
    The University of Auckland Library

    This paper presents two novel interdependent techniques for random digital simple curve generation. The first one is about generating a curve of finite length, producing a sequence of points defining a digital path ρ ‘on the fly’. The second is for the creation of artistic sketches from line drawings and edge maps, using multiple instances of such random digital paths. A generated digital path ρ never intersects or touches itself, and hence becomes simple and irreducible. This is ensured by detecting every possible trap formed by the previously generated part of ρ, which, if entered into, cannot be exited without touching or intersecting ρ. The algorithm is completely free of any backtracking and its time complexity is linear in the length of ρ. For artistic emulation, a curve-constrained domain is defined by the Minkowski sum of the input drawing with a structuring element whose size varies with the pencil diameter. An artist’s usual trait of making irregular strokes and sub-strokes, with varying shades while sketching, is thus captured in a realistic manner. Algorithmic solutions of non-photorealism are perceived as an enrichment of contemporary digital art. Simulation results for the presented algorithms have been furnished to demonstrate their efficiency and elegance.

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  • Hybrid Filter Blending to Maintain Facial Expressions in Rendered Human Portraits

    Rezaei, Mahdi; Lin, J; Klette, Reinhard (2014)

    Journal article
    The University of Auckland Library

    Artistic rendering of human portraits is different and more challenging than that of landscapes or flowers. Issues are eye, nose, and mouth regions (i.e., facial features) where we need to represent their natural emotions. Shades or darkness around eyes, or shininess at nose tips may negatively impact the rendering result if not properly dealt with. Similarly, a lighter colour around the mouth region caused by lighting might produce some disturbing artefacts. The proposed computerised method attempts to be adaptive to those sensitive areas by utilising a face analysis module. First, the program detects main facial segments and features. Then it utilises a blending of various filtering parameters aiming at an adequate final portrait that represents the subject's original facial expression, while still supporting a non-photorealistic artistic rendering as the perceived impression.

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  • Evaluation of two stereo matchers on long real-world video sequences

    Shin, B-S; Caudillo, D; Klette, Reinhard (2015)

    Journal article
    The University of Auckland Library

    The paper evaluates iterative semi-global matching (iSGM) and linear belief-propagation matching (linBPM), both using a census data-cost function, which are two of the currently top-ranked stereo matchers. The evaluation is on long real-world video sequences where disparity ground-truth is not available. The paper applies two alternative (or mutually supporting) techniques for performance evaluation: the previously known third-eye method, and a few new data measures on video sequences. The main contribution of the paper is on answering the questions, how to evaluate stereo matchers on long real-world sequences if disparity ground truth is not available, and how to compare evaluation measures relatively to each other. The two stereo matchers used are illustrating the discussed evaluation measures; they could be replaced by other matchers, but evaluation results for those two matchers are also of interest on its own, by illustrating correlations in the behavior of those two basically very different matchers (defined by dynamic programming or by belief propagation optimization, respectively) on data sequences recorded in different traffic situations.

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  • Approximate shortest routes for frontier visibility under limited visibility

    Chen, X; Li, F; Klette, Reinhard (2012)

    Journal article
    The University of Auckland Library

    Consider a simple polygon P and a point s on the frontier @P of P. For any real > 0 there exists a shortest path inside of P such that s is on the path , and for each point p in @P, there exists a point q in at Euclidean distance less than or equal to p such that the line segment pq is in P. Such an optimum path is called a shortest route for @P visibility under -visibility that starts at point s on @P. We provide an approximation algorithm (which belongs to the class of rubberband algorithms) for finding such a path in O(n2) run time, where n is the number of vertices of a given simple polygon P. The run time does not depend on or on the start point s.

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  • Border and surface tracing - Theoretical foundations

    Brimkov, VE; Klette, Reinhard (2008)

    Journal article
    The University of Auckland Library

    In this paper, we define and study digital manifolds of arbitrary dimension, and provide (in particular) a general theoretical basis for curve or surface tracing in picture analysis. The studies involve properties such as the one-dimensionality of digital curves and (n - 1)-dimensionality of digital hypersurfaces that makes them discrete analogs of corresponding notions in continuous topology. The presented approach is fully based on the concept of adjacency relation and complements the concept of dimension, as common in combinatorial topology. This work appears to be the first one on digital manifolds based on a graph-theoretical definition of dimension. In particular, in the n-dimensional digital space, a digital curve is a one-dimensional object and a digital hypersurface is an (n - 1)-dimensional object, as it is in the case of curves and hypersurfaces in the Euclidean space. Relying on the obtained properties of digital hypersurfaces, we propose a uniform approach for studying good pairs defined by separations and obtain a classification of good pairs in arbitrary dimension. We also discuss possible applications of the presented definitions and results.

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  • Performance of Correspondence Algorithms in Vision-Based Driver Assistance Using an Online Image Sequence Database

    Klette, Reinhard; Kruger, Norbert; Vaudrey, Tobi; Pauwels, Karl; van Hulle, Marc; Morales, Sandino; Kandil, Farid I; Haeusler, Ralf; Pugeault, Nicolas; Rabe, Clemens; Lappe, Markus (2011-06)

    Journal article
    The University of Auckland Library

    This paper discusses options for testing correspondence algorithms in stereo or motion analysis that are designed or considered for vision-based driver assistance. It introduces a globally available database, with a main focus on testing on video sequences of real-world data. We suggest the classification of recorded video data into situations defined by a cooccurrence of some events in recorded traffic scenes. About 100-400 stereo frames (or 4-16 s of recording) are considered a basic sequence, which will be identified with one particular situation. Future testing is expected to be on data that report on hours of driving, and multiple hours of long video data may be segmented into basic sequences and classified into situations. This paper prepares for this expected development. This paper uses three different evaluation approaches (prediction error, synthesized sequences, and labeled sequences) for demonstrating ideas, difficulties, and possible ways in this future field of extensive performance tests in vision-based driver assistance, particularly for cases where the ground truth is not available. This paper shows that the complexity of real-world data does not support the identification of general rankings of correspondence techniques on sets of basic sequences that show different situations. It is suggested that correspondence techniques should adaptively be chosen in real time using some type of statistical situation classifiers.

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  • An Approach for Evaluating Robustness of Edge Operators using Real-World Driving Scenes

    Al-Sarraf, Ali; Vaudrey, Tobi; Klette, Reinhard; Woo, Young Woon (2008)

    Conference poster
    The University of Auckland Library

    Conference Details: 2008 23rd International Conference Image and Vision Computing New Zealand Lincoln University, Christchurch, 26-28 November 2008. http://www.lvl.co.nz/ivcnz2008/ Over the past 20 years there have been many papers that compare and evaluate di erent edge operators. Most of them focus on accuracy and also do comparisons against synthetic data. This paper focuses on real-world driver assistance scenes and does a comparison based on robustness. The three edge operators compared are Sobel, Canny and the under-publicized phase-based Kovesi-Owens operator. The Kovesi- Owens operator has the distinct advantage that it uses one pre-selected set of parameters and can work across almost any type of scene, where as other operators require parameter tuning. The results from our comparison show that the Kovesi-Owens operator is the most robust of the three, and can get decent results, even under weak illumination and varying gradients in the images. Keywords: edge operators, edge robustness evaluation, Kovesi-Owens, phase operators

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  • A Variant of Adaptive Mean Shift-Based Clustering

    Li, Fajie; Klette, Reinhard (2008)

    Conference poster
    The University of Auckland Library

    Conference Details: ICONIP 2008 - 15th International Conference on Neural Information. Processing of the Asia-Pacific Neural Network Assembly November 25-28, 2008, Auckland, New Zealand We are interested in clustering sets of highly overlapping clusters. For example, given is an observed set of stars (considered to be a set of points); how to find (recover) clusters which are the contributing galaxies of the observed union of those clusters? Below we propose a modification of an adaptive mean shift-based clustering algorithm (called Algorithm 1) proposed in 2003 by B. Geogescu, I. Shimsoni and P. Meer

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  • Approximated Ground Truth for Stereo and Motion Analysis on Real-World Sequences (Poster)

    Liu, Zhifeng; Klette, Reinhard (2009)

    Conference poster
    The University of Auckland Library

    Conference details: The 3rd Pacific-Rim Symposium on Image and Video Technology (PSIVT2009) Tokyo, Japan, January 13th—16th, 2009 http://psivt2009.nii.ac.jp/ We approximate ground truth for real-world stereo sequences and demonstrate its use for the performance analysis of a few selected stereo matching and optic flow techniques. Basically we assume zero roll and constant tilt of an ego-vehicle (for about 10 seconds) driving on a planar road.

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  • Inclusion of a Second-Order Prior into Semi-Global Matching. (2009)

    Hermann, Simon; Klette, Reinhard; Destenfanis, Eduardo (2009)

    Conference poster
    The University of Auckland Library

    Conference details: The 3rd Pacific-Rim Symposium on Image and Video Technology (PSIVT2009) Tokyo, Japan, January 13th—16th, 2009 http://psivt2009.nii.ac.jp/ We consider different parameter settings for SGM, suggest to include a second order prior into the smoothness term of the energy function, and propose and test a new cost function. Some preprocessing (edge images) proves to be of value for improving SGM stereo results on real-world data.

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