[Show abstract][Hide abstract] ABSTRACT: Cell nuclei detection in fluorescent microscopic images is an important and time consuming task in a wide range of biological applications. Blur, clutter, bleed through and partial occlusion of nuclei make individual nuclei detection a challenging task for automated image analysis. This paper proposes a novel and robust detection method based on the active contour framework. Improvement over conventional approaches is achieved by exploiting prior knowledge of the nucleus shape in order to better detect individual nuclei. This prior knowledge is defined using a dictionary based approach which can be formulated as the optimization of a convex energy function. The proposed method shows accurate detection results for dense clusters of nuclei, for example, an F-measure (a measure for detection accuracy) of 0.96 for the detection of cell nuclei in peripheral blood mononuclear cells, compared to an F-measure of 0.90 achieved by state-of-the-art nuclei detection methods.
PLoS ONE 01/2013; 8(1):e54068. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A mobile mapping system (MMS) is the answer of the geoinformation community to the exponentially growing demand for various geospatial data with increasingly higher accuracies, captured by multiple sensors. As the mobile mapping technology is pushed to explore its use for various applications on water, rail, or road, the need emerges to have an external sensor calibration procedure that is portable, fast and easy to perform. This way, sensors can be mounted and demounted depending on the application requirements without the need for time consuming calibration procedures. A new methodology is presented to provide a high quality external calibration of cameras which is automatic, robust and fool proof. The method uses a portable, standard ranging pole which needs to be positioned on a known ground control point. While the literature focuses on solving the absolute orientation problem of the calibration, an automatic method to detect the calibration object is missing. Here, we present a mutual information based image registration technique for automatic sub-pixel localization of the ranging pole under realistic outdoor conditions. We include several robust error detection rules to allow the calibration to run without human intervention, giving as little outliers as possible, to ensure a correct calibration. Several tests are performed under various lighting and noise conditions which prove the methodology’s robustness.
ISPRS Journal of Photogrammetry and Remote Sensing 01/2013; 86:111–123. · 3.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A mobile mapping system (MMS) is the answer of the geoinformation
community to the exponentially growing demand for various geospatial
data with increasingly higher accuracies and captured by multiple
sensors. As the mobile mapping technology is pushed to explore its use
for various applications on water, rail, or road, the need emerges to
have an external sensor calibration procedure which is portable, fast
and easy to perform. This way, sensors can be mounted and demounted
depending on the application requirements without the need for time
consuming calibration procedures. A new methodology is presented to
provide a high quality external calibration of cameras which is
automatic, robust and fool proof.The MMS uses an Applanix POSLV420,
which is a tightly coupled GPS/INS positioning system. The cameras used
are Point Grey color video cameras synchronized with the GPS/INS system.
The method uses a portable, standard ranging pole which needs to be
positioned on a known ground control point. For calibration a well
studied absolute orientation problem needs to be solved. Here, a mutual
information based image registration technique is studied for automatic
alignment of the ranging pole. Finally, a few benchmarking tests are
done under various lighting conditions which proves the methodology's
robustness, by showing high absolute stereo measurement accuracies of a
[Show abstract][Hide abstract] ABSTRACT: Micro-structures of surface are considered to be effective in identifying the damage mechanisms. The industry uses computer vision to auto detect misalignment of the components as it is a contactless tool. However, in scientific investigations micro structures obtained online at high-speed has to be analyzed. In this work the change detection of a specimen rotating at a high speed studied online using image processing techniques in micro graphs which provides a clear insight about the dimensional changes. The specimen under study is made from polymer composite which has contact with a steel wheel and rotates at a high speed. The blur as a measure of dimensional change of the polymer composite can be identified due to the change in focus. The micro-structure images were dark and span a very small region of the surface due to high speed image acquisition, short shutter time and magnification of the microscope. Thus, pre-processing procedures like image enhancement, stitching and registration are performed. Then 15 blur estimation methods are applied to the stitched images. The results of three methods present a good correlation with dimensional change provided by a stylus instrument.
Proceedings of the 14th international conference on Advanced Concepts for Intelligent Vision Systems; 09/2012
[Show abstract][Hide abstract] ABSTRACT: Intensity based image registration methods are necessary in situations where feature point based methods fail, e.g multispectral images or images with repetitive textures. However the higher robustness comes at the cost of being slower than the feature point alternative. This problem can be alleviated by subsampling the pixels used to calculate the intensity matching criterion. Unfortunately there are no guidelines for the amount of allowed subsampling. In this paper we present a model for a lower bound on the number of pixel samples in image sets to keep a certain confidence about the correctness of the result, using the variance on the estimated mutual information value. With this model we can speed up the intensity based registration while remaining confident about getting correct results.
Proc. of the IEEE International Conference on Image Processing (ICIP2012); 09/2012
[Show abstract][Hide abstract] ABSTRACT: Studying wear process by effective means avoids undesirable situation such as frequent replacement of components, breakdown-maintenance and catastrophic accidents. In tribological investigations, dimensional changes due to wear processes are assessed using offline and online techniques. However, traditional postmortem analysis cannot display intermediate wear mechanisms. Visible textures as a direct measure of wear is a valuable evidence to understand tribological characteristics. In recent years, online-monitoring through computer vision has been used to study surface roughness. Nevertheless, online-monitoring for topographical and microstructural changes during wear could provide a clear insight of wear process. In this work, attempts are made to monitor rolling/sliding contact using a high-speed camera in conjunction with a microscope. Optical and imaging parameters were optimised to obtain clear images. Tests were conducted using polymer composite for understanding the contact surface topography of the wear process. Micrographs of the composite contact surface were acquired online using 35,000 fps and 0.375 ns shutterspeed. Periodical changes in wear mechanism are evident with resin back transfer, surface cracks and partial exposure of fibres. Thus, effective characterisation through online-monitoring gives a clear insight of the fundamental mechanisms behind wear process. The newly developed high speed imaging system stands as an effective tool in tribological investigations.
[Show abstract][Hide abstract] ABSTRACT: Registration of multispectral images remains a challenging task due to
the lack of stable feature points. Methods based on intensities are
generally more robust for multi-modal image registration, but are
computationally demanding or are restrictive to the transformation model
allowed in the registration. This paper proposes a new registration
framework which overcomes these drawbacks. The proposed method optimizes
the location of a set of virtual landmarks in order to get robust and
SPIE Proc. of Sensing for Agriculture and Food Quality and Safety; 04/2012
[Show abstract][Hide abstract] ABSTRACT: The topic of registering multi- and hyperspectral imagery is well studied in literature. However when the registration must be done between multispectral images and vector data, the literature is more limited. In this paper we focus on registering aerial images in the thermal (IR) band, and vector data delineating houses and other man-made structures in the same region. This differs from classical registration because first of all, the vector data is not in the same format as the thermal image (i.e. vectors versus pixels), although it can be rasterized initially. Secondly, feature points fail to match between the two representations while intensity based methods also have problems due to the large changes between the rasterized vector and thermal images. We present a method based on a modified version of mutual information that outperforms existing methods for these specific inputs.
2011 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011, Vancouver, BC, Canada, July 24-29, 2011; 01/2011
[Show abstract][Hide abstract] ABSTRACT: Our surroundings change all the time. Applications that require 3D models of a changing terrain, such as urban planning, are becoming ever more demanding with respect to the cost to create them and the accuracy of the result. A novel, cheap and fast solution for this problem is given by a UAV to take aerial images of the terrain in question, in combination with structure from motion algorithms to create a 3D model from those aerial images. However the question remains whether these on-the-fly 3D maps can match the accuracy of classical surveyor based models, which require more time to create. In this paper we investigate this question, and find that under certain conditions the accuracy of the UAV based model matches the accuracy of surveyor generated measurements.
Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International; 08/2010
[Show abstract][Hide abstract] ABSTRACT: The dynamics of genome regions are associated to the functional or dysfunctional behaviour of the human cell. In order to study these dynamics it is necessary to remove perturbations coming from movement and deformation of the nucleus, i.e. the container holding the genome. In literature models have been proposed to cope with the transformations corresponding to nuclear dynamics of healthy cells. However for pathological cells, the nucleus deforms in an apparently random way, making the use of such models a non trivial task. In this paper we propose a mapping of the cell nucleus which is based on the matching of the nuclear contours. The proposed method does not put constraints on the possible shapes nor on the possible deformations, making this method suited for the analysis of pathological nuclei.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:4379-82.
[Show abstract][Hide abstract] ABSTRACT: Active contours or snakes are widely used for segmentation and tracking. We propose a new active contour model, which converges
reliably even when the initialization is far from the object of interest. The proposed segmentation technique uses an external
energy function where the energy slowly decreases in the vicinity of an edge. Based on this energy a new external force field
is defined. Both energy function and force field are calculated using an efficient dual scan line algorithm. The proposed
force field is tested on computational speed, its effect on the convergence speed of the active contour and the segmentation
result. The proposed method gets similar segmentation results as the gradient vector flow and vector field convolution active contours, but the force field needs significantly less time to calculate.
Advanced Concepts for Intelligent Vision Systems - 12th International Conference, ACIVS 2010, Sydney, Australia, December 13-16, 2010, Proceedings, Part I; 01/2010
[Show abstract][Hide abstract] ABSTRACT: Structure from motion based D reconstruction takes a lot of time for large scenes which consist of thousands of input images.
We propose a method that speeds up the reconstruction of large scenes by partitioning it into smaller scenes, and then recombining
those. The main benefit here is that each subscene can be optimized in parallel. We present a widely usable subdivision method,
and show that the difference between the result after partitioning and recombination, and the state of the art structure from
motion reconstruction on the entire scene, is negligible.
Advanced Concepts for Intelligent Vision Systems - 12th International Conference, ACIVS 2010, Sydney, Australia, December 13-16, 2010, Proceedings, Part II; 01/2010
[Show abstract][Hide abstract] ABSTRACT: Due to weight constraints, UAVs often carry cameras with lenses that create distortions in the image. For practical applications this distortion should be removed with a proper calibration procedure, without spending too much extra time. Existing methods require costly manual interaction when the grid is not fully visible, or when not all points can be extracted. In this paper we present an algorithm to perform the calibration without any user interaction whatsoever, which works under almost all possible conditions. The only inputs are a number of pictures of a checkerboard, taken with the camera. We extract the corners from the chessboard pictures, and set up a world coordinate grid that is robust to missing corner points, occlusion and deformations. We automatically omit the pictures that are too close to another picture, to avoid giving too much weight to often viewed areas. Finally we optimize the result by iteratively removing outlier pictures from the set.
Geoscience and Remote Sensing Symposium,2009 IEEE International,IGARSS 2009; 08/2009
[Show abstract][Hide abstract] ABSTRACT: Very high spatial resolution satellite images allow to identify individual man-made objects. However, automatic extraction of these objects is still very difficult, especially in urban areas. Spectral information is insufficient to separate the different man-made object classes. Therefore, there is an increased interest in incorporating shape and contextual information in the classification process. Object-based approaches provide a straightforward method to incorporate both shape and contextual information. However, these approaches require a segmentation of the image, which is a very difficult and sensitive task, especially in urban areas. Recently some attempts have been made to incorporate shape information on a pixel basis. In this paper we further develop this approach and propose a method to also derive contextual information on a pixel basis. The per-pixel features developed in this paper contain information about the distance from the object the pixel belongs to to the nearest shadow object. Clearly, this information can be helpful to identify buildings, which are generally accompanied by shadow. However, the proposed method can also be used to describe other contextual information.