| 1. |
- Allalou, Amin, et al.
(author)
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Image Based Measurements of Single Cell mtDNA Mutation Load
- 2007
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In: Image Analysis, Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540730392 ; , s. 631-640
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Conference paper (peer-reviewed)abstract
- Cell cultures as well as cells in tissue always display a certain degree of variability, and measurements based on cell averages will miss important information contained in a heterogeneous population. This paper presents automated methods for image based measurements of mitochondiral DNA (mtDNA) mutations in individual cells. The mitochondria are present in the cell’s cytoplasm, and each cytoplasm has to be delineated. Three different methods for segmentation of cytoplasms are compared and it is shown that automated cytoplasmic delineation can be performed 30 times faster than manual delineation, with an accuracy as high as 87%. The final image based measurements of mitochondrial mutation load are also compared to, and show high agreement with, measurements made using biochemical techniques.
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| 2. |
- Brun, Anders, 1976-, et al.
(author)
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Using Importance Sampling for Bayesian Feature Space Filtering
- 2007
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In: Proceedings of the 15th Scandinavian conference on image analysis. - Berlin, Heidelberg : Springer-Verlag. - 9783540730392 ; , s. 818-827
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Conference paper (peer-reviewed)abstract
- We present a one-pass framework for filtering vector-valued images and unordered sets of data points in an N-dimensional feature space. It is based on a local Bayesian framework, previously developed for scalar images, where estimates are computed using expectation values and histograms. In this paper we extended this framework to handle N-dimensional data. To avoid the curse of dimensionality, it uses importance sampling instead of histograms to represent probability density functions. In this novel computational framework we are able to efficiently filter both vector-valued images and data, similar to e.g. the well-known bilateral, median and mean shift filters.
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| 3. |
- Cornelius, Hugo, et al.
(author)
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Efficient symmetry detection using local affine frames
- 2007
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In: Image Analysis, Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540730392 ; , s. 152-161
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Conference paper (peer-reviewed)abstract
- We present an efficient method for detecting planar bilateral symmetries under perspective projection. The method uses local affine frames (LAFs) constructed on maximally stable extremal regions or any other affine covariant regions detected in the image to dramatically improve the process of detecting symmetric objects under perspective distortion. In contrast to the previous work no Hough transform, is used. Instead, each symmetric pair of LAFs votes just once for a single axis of symmetry. The time complexity of the method is n log(n), where n is the number of LAFs, allowing a near real-time performance. The proposed method is robust to background clutter and partial occlusion and is capable of detecting an arbitrary number of symmetries in the image.
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| 4. |
- Felsberg, Michael, et al.
(author)
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Real-Time Visual Recognition of Objects and Scenes Using P-Channel Matching
- 2007
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In: Proceedings 15th Scandinavian Conference on Image Analysis. - Berlin, Heidelberg : Springer. - 9783540730392 ; , s. 908-917
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Conference paper (peer-reviewed)abstract
- In this paper we propose a new approach to real-time view-based object recognition and scene registration. Object recognition is an important sub-task in many applications, as e.g., robotics, retrieval, and surveillance. Scene registration is particularly useful for identifying camera views in databases or video sequences. All of these applications require a fast recognition process and the possibility to extend the database with new material, i.e., to update the recognition system online. The method that we propose is based on P-channels, a special kind of information representation which combines advantages of histograms and local linear models. Our approach is motivated by its similarity to information representation in biological systems but its main advantage is its robustness against common distortions as clutter and occlusion. The recognition algorithm extracts a number of basic, intensity invariant image features, encodes them into P-channels, and compares the query P-channels to a set of prototype P-channels in a database. The algorithm is applied in a cross-validation experiment on the COIL database, resulting in nearly ideal ROC curves. Furthermore, results from scene registration with a fish-eye camera are presented.
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| 5. |
- Fundana, Ketut, et al.
(author)
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Variational Segmentation of Image Sequences using Deformable Shape Priors
- 2007
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In: Image Analysis. - Berlin, Heidelberg : Springer. - 9783540730392 - 9783540730408
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Conference paper (peer-reviewed)abstract
- The segmentation of objects in image sequences is an important and difficult problem in computer vision with applications to e.g. video surveillance. In this paper we propose a new method for variational segmentation of image sequences containing nonrigid, moving objects. The method is based on the classical Chan-Vese model augmented with a novel frame-to-frame interaction term, which allow us to update the segmentation result from one image frame to the next using the previous segmentation result as a shape prior. The interaction term is constructed to be pose-invariant and to allow moderate deformations in shape. It is expected to handle the appearance of occlusions which otherwise can make segmentation fail. The performance of the model is illustrated with experiments on real image sequences.
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| 6. |
- Georgsson, Fredrik, 1971-, et al.
(author)
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Fractal Analysis of Mammograms
- 2007
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In: SCIA 2007. - Berlin : Springer. - 9783540730392 ; , s. 92-101
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Conference paper (peer-reviewed)abstract
- In this paper it is shown that there is a difference in local fractal dimension between imaged glandular tissue, supporting tissue and muscle tissue based on an assessment from a mammogram. By estimating the density difference at four different local dimensions (2.06, 2.33, 2.48, 2.70) from 142 mammograms we can define a measure and by using this measure we are able to distinguish between the tissue types. A ROC-analysis gives us an area under the curve-value of 0.9998 for separating glandular tissue from muscular tissue and 0.9405 for separating glandular tissue from supporting tissue. To some extent we can say that the measured difference in fractal properties is due to different fractal properties of the unprojected tissue. For example, to a large extent muscle tissue seems to have different fractal properties than glandular or supportive tissue. However, a large variance in the local dimension densities makes it difficult to make proper use of the proposed measure for segmentation purposes.
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| 7. |
- Hedström, Erik, et al.
(author)
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Model based cardiac motion tracking using velocity encoded magnetic resonance imaging
- 2007
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In: Image Analysis (Lecture Notes in Computer Science). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0302-9743 .- 1611-3349. - 9783540730392 ; 4522, s. 82-91
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Conference paper (peer-reviewed)abstract
- This paper deals with model based regularization of velocity encoded cardiac magnetic resonance images (MRI). We extend upon an existing spatiotemporal model of cardiac kinematics by considering data certainty and regularity of the model in order to improve its performance. The method was evaluated using a computer simulated phantom and using in vivo gridtag MRI as gold standard. We show, both quantitatively and qualitatively, that our modified model performs better than the original one.
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| 8. |
- Herberthson, Magnus, 1963-, et al.
(author)
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Representing Pairs of Orientations in the Plane
- 2007
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In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 661-670
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Conference paper (peer-reviewed)abstract
- In this article we present a way of representing pairs of orientations in the plane. This is an extension of the familiar way of representing single orientations in the plane. Using this framework, pairs of lines can be added, scaled and averaged over in a sense which is to be described. In particular, single lines can be incorporated and handled simultaneously.
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| 9. |
- Heyden, Anders, et al.
(author)
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Recursive Structure and Motion Estimation based on Hybrid Matching Constraints
- 2007
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In: Image Analysis. - Berlin, Heidelberg : Springer. - 9783540730392 - 9783540730408
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Conference paper (peer-reviewed)abstract
- Motion estimation has traditionally been approached either from a pure discrete point of view, using multi-view tensors, or from a pure continuous point of view, using optical flow. This paper builds upon a novel framework of hybrid matching constraints for motion estimation, combining the advantages of both discrete and continuous methods. We will derive both bifocal and trifocal hybrid constraints and use them together with a structure estimate based on filtering techniques. A feedback from the structure estimate will be used to further refine the motion estimate. This gives a complete iterative structure and motion estimation scheme. Its performance will be demonstrated in simulated experiments.
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| 10. |
- Jonsson, Erik, 1980-, et al.
(author)
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Accurate Interpolation in Appearance-Based Pose Estimation
- 2007
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In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 1-10
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Conference paper (peer-reviewed)abstract
- One problem in appearance-based pose estimation is the need for many training examples, i.e. images of the object in a large number of known poses. Some invariance can be obtained by considering translations, rotations and scale changes in the image plane, but the remaining degrees of freedom are often handled simply by sampling the pose space densely enough. This work presents a method for accurate interpolation between training views using local linear models. As a view representation local soft orientation histograms are used. The derivative of this representation with respect to the image plane transformations is computed, and a Gauss-Newton optimization is used to optimize all pose parameters simultaneously, resulting in an accurate estimate.
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| 11. |
- Josephson, Klas, et al.
(author)
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Triangulation of Points, Lines and Conics
- 2007
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In: Image Analysis (Lecture Notes in Computer Science). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1611-3349 .- 0302-9743. - 9783540730392 ; 4522, s. 162-172
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Conference paper (peer-reviewed)abstract
- The problem of reconstructing 3D scene features from multiple views with known camera motion and given image correspondences is considered. This is a classical and one of the most basic geometric problems in computer vision and photogrammetry. Yet, previous methods fail to guarantee optimal reconstructions - they are either plagued by local minima or rely on a non-optimal cost-function. A common framework for the triangulation problem of points, lines and conics is presented. We define what is meant by an optimal triangulation based on statistical principles and then derive an algorithm for computing the globally optimal solution. The method for achieving the global minimum is based on convex and concave relaxations for both fractionals and monomials. The performance of the method is evaluated on real image data.
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| 12. |
- Kollreider, Klaus, et al.
(author)
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Real-Time Face Detection Using Illumination Invariant Features
- 2007
-
In: Image Analysis. - Berlin : Springer. - 9783540730392 ; , s. 41-50
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Conference paper (peer-reviewed)abstract
- A robust object/face detection technique processing every frame in real-time (video-rate) is presented. A methodological novelty are the suggested quantized angle features (“quangles”), being designed for illumination invariance without the need for pre-processing, e.g. histogram equalization. This is achieved by using both the gradient direction and the double angle direction (the structure tensor angle), and by ignoring the magnitude of the gradient. Boosting techniques are applied in a quantized feature space. Separable filtering and the use of lookup tables favor the detection speed. Furthermore, the gradient may then be reused for other tasks as well. A side effect is that the training of effective cascaded classifiers is feasible in very short time, less than 1 hour for data sets of order 104. We present favorable results on face detection, for several public databases (e.g. 93% Detection Rate at 1×10− 6 False Positive Rate on the CMU-MIT frontal face test set).
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| 13. |
- Latorre Carmona, Pedro, et al.
(author)
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Affine Illumination Compensation for Multispectral Images
- 2007
-
In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 522-531
-
Conference paper (peer-reviewed)abstract
- We apply a general form of affine transformation model to compensate illumination variations in a series of multispectral images of a static scene and compare it to a particular affine and a diagonal transformation models. These models operate in the original multispectral space or in a lower-dimensional space obtained by Singular Value Decomposition (SVD) of the set of images. We use a system consisting of a multispectral camera and a light dome that allows the measurement of multispectral data under carefully controlled illumination conditions to generate a series of multispectral images of a static scene under varying illumination conditions. We evaluate the compensation performance using the CIELAB colour difference between images. The experiments show that the first 2 models perform satisfactorily in the original and lower dimensional spaces.
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| 14. |
- Nordberg, Klas, 1963-
(author)
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A linear mapping for stereo triangulation
- 2007
-
In: Scandiavian Conference on Image Analysis (SCIA). - Springer : Berlin / Heidelberg. - 9783540730392
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Conference paper (peer-reviewed)abstract
- A novel and computationally simple method is presented for triangulation of 3D points corresponding to the image coordinates in a pair of stereo images. The image points are described in terms of homogeneous coordinates which are jointly represented as the outer products of these homogeneous coordinates. This paper derives a linear transformation which maps the joint representation directly to the homogeneous representation of the corresponding 3D point in the scene. Compared to the other triangulation methods this approach gives similar reconstruction error but is numerically faster, since it only requires linear operations. The proposed method is projective invariant in the same way as the optimal method of Hartley and Sturm. The methods has a "blind plane"; a plane through the camera focal points which cannot be reconstructed by this method. For "forward-looking" camera configurations, however, the blind plane can be placed outside the visible scene and does not constitute a problem.
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| 15. |
- Nyström, Daniel, 1974-
(author)
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Colorimetric and Multispectral Image Acquisition Using Model-based and Empirical Device Characterization
- 2007
-
In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 798-807
-
Conference paper (peer-reviewed)abstract
- The focus of the study is high quality image acquisition in colorimetric and multispectral formats. The aim is to combine the spatial resolution of digital images with the spectral resolution of color measurement instruments, to allow for accurate colorimetric and spectral measurements in each pixel of the acquired images. An experimental image acquisition system is used, which besides trichromatic RGB filters also provides the possibility of acquiring multi-channel images, using a set of narrowband filters. To derive mappings to colorimetric and multispectral representations, two conceptually different approaches are used. In the model-based characterization, the physical model describing the image acquisition process is inverted, to reconstruct spectral reflectance from the recorded device response. In the empirical characterization, the characteristics of the individual components are ignored, and the functions are derived by relating the device response for a set of test colors to the corresponding colorimetric and spectral measurements, using linear and polynomial least squares regression. The results indicate that for trichromatic imaging, accurate colorimetric mappings can be derived by the empirical approach, using polynomial regression to CIEXYZ and CIELAB. However, accurate spectral reconstructions requires for multi-channel imaging, with the best results obtained using the model-based approach.
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| 16. |
- Rodríguez-Vila, Borja, et al.
(author)
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3D deformable registration for monitoring radiotherapy treatment in prostate cancer
- 2007
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In: Image Analysis. - Berlin/Heidelberg, Germany : Springer Berlin/Heidelberg. - 9783540730392 - 3540730400 - 9783540730408 ; , s. 750-759
-
Conference paper (peer-reviewed)abstract
- Two deformable registration methods, the Demons and the Morphon algorithms, have been used for registration of CT datasets to evaluate their usability in radiotherapy planning for prostate cancer. These methods were chosen because they can perform deformable registration in a fully automated way. The experiments show that for intrapatient registration both of the methods give useful results, although some differences exist in the way they deform the template. The Morphon method has, however, some advantageous compared to the Demons method. It is invariant to the image intensity and it does not distort the deformed data. The conclusion is therefore to recommend the Morphon method as a registration tool for this application. A more flexible regularization model is needed, though, in order to be able to catch the full range of deformations required to match the datasets.
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| 17. |
- Skoglund, Johan, 1978-, et al.
(author)
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Covariance estimation for SAD block matching
- 2007
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In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 374-382
-
Conference paper (peer-reviewed)abstract
- The estimation of a patch position in an image is a long established but still relevant topic with many applications, e.g. pose estimation and tracking in image sequences. In most systems the position estimate needs to be fused with other estimates, and hence, covariance information is required to weight the different estimates in the right way. In this paper we address the issue with covariance estimation in the case of sum of absolute difference (SAD) block matching. First, we derive the theory for covariance estimation in the case of SAD matching. Second, we evaluate the suggested method in a virtual 3D patch tracking scenario in order to verify the performance in real-world scenarios.
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| 18. |
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| 19. |
- Solli, Martin, 1980-, et al.
(author)
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FyFont: Find-your-Font in Large Font Databases
- 2007
-
In: Scandinavian Conference on Image Analysis, SCIA 2007. - Berlin : Springer. - 9783540730392 ; , s. 432-441
-
Conference paper (peer-reviewed)abstract
- A search engine for font recognition in very large font data-bases is presented and evaluated. The search engine analyzes an image of a text line, and responds with the name of the font used when writing the text. After segmenting the input image into single characters, the recognition is mainly based on eigenimages calculated from edge filtered character images. We evaluate the system with printed and scanned text lines and character images. The database used contains 2763 different fonts from the English alphabet. Our evaluation shows that for 99.8 % of the queries, the correct font name is one of the five best matches. Apart from finding fonts in large databases, the search engine can also be used as a pre-processor for Optical Character Recognition.
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| 20. |
- Strand, Robin
(author)
-
Weighted Distances Based on Neighbourhood Sequences in Non-Standard Three-Dimensional Grids
- 2007
-
In: Image Analysis, Proceedings. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540730392 ; , s. 452-461
-
Conference paper (peer-reviewed)abstract
- By combining weighted distances and distances based on neighbourhood sequences, a new family of distance functions with potentially low rotational dependency is obtained. The basic theory for these distance functions, including functional form of the distance between two points, is presented for the face-centered cubic grid and the body-centered cubic grid. By minimizing an error function, the optimal combination of weights and neighbourhood sequence is derived.
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| 21. |
- Svensson, Björn, et al.
(author)
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Estimation of Non-Cartesian Local Structure Tensor Fields
- 2007
-
In: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 948-957
-
Conference paper (peer-reviewed)abstract
- In medical imaging, signals acquired in non-Cartesian coordinate systems are common. For instance, CT and MRI often produce significantly higher resolution within scan planes, compared to the distance between two adjacent planes. Even oblique sampling occurs, by the use of gantry tilt. In ultrasound imaging, samples are acquired in a polar coordinate system, which implies a spatially varying metric.In order to produce a geometrically correct image, signals are generally resampled to a Cartesian coordinate system. This paper concerns estimation of local structure tensors directly from the non-Cartesian coordinate system, thus avoiding deteriorated signal and noise characteristics caused by resampling. In many cases processing directly in the warped coordinate system is also less time-consuming. A geometrically correct tensor must obey certain transformation rules originating from fundamental differential geometry. Subsequently, this fact also affects the tensor estimation. As the local structure tensor is estimated using filters, a change of coordinate system also change the shape of the spatial support of these filters. Implications and limitations brought on by sampling require the filter design criteria to be adapted to the coordinate system.
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| 22. |
- Teferi, Dereje, et al.
(author)
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Text Driven Face-Video Synthesis Using GMM and Spatial Correlation
- 2007
-
In: Image analysis. - Berlin : Springer Berlin/Heidelberg. - 9783540730392 ; , s. 572-580
-
Conference paper (peer-reviewed)abstract
- Liveness detection is increasingly planned to be incorporated into biometric systems to reduce the risk of spoofing and impersonation. Some of the techniques used include detection of motion of the head while posing/speaking, iris size in varying illumination, fingerprint sweat, text-prompted speech, speech-to-lip motion synchronization etc. In this paper, we propose to build a biometric signal to test attack resilience of biometric systems by creating a text-driven video synthesis of faces. We synthesize new realistic looking video sequences from real image sequences representing utterance of digits. We determine the image sequences for each digit by using a GMM based speech recognizer. Then, depending on system prompt (sequence of digits) our method regenerates a video signal to test attack resilience of a biometric system that asks for random digit utterances to prevent play-back of pre-recorded data representing both audio and images. The discontinuities in the new image sequence, created at the connection of each digit, are removed by using a frame prediction algorithm that makes use of the well known block matching algorithm. Other uses of our results include web-based video communication for electronic commerce and frame interpolation for low frame rate video.
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| 23. |
- Åström, Karl, et al.
(author)
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Automatic feature point correspondences and shape analysis with missing data and outliers using MDL
- 2007
-
In: Proceedings 15th Scandinavian Image Analysis Conference. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540730392 ; 4522, s. 21-30
-
Conference paper (peer-reviewed)abstract
- Automatic construction of shape models from examples has recently been the focus of intense research. These methods have proved to be useful for shape segmentation, tracking, recognition and shape understanding. In this paper we discuss automatic landmark selection and correspondence determination from a discrete set of landmarks, typically obtained by feature extraction. The set of landmarks may include both outliers and missing data. Our framework has a solid theoretical basis using principles of minimal description length (MDL). In order to exploit these ideas, new non-heuristic methods for (i) principal component analysis and (ii) procrustes mean are derived - as a consequence of the modelling principle. The resulting MDL criterion is optimised over both discrete and continuous decision variables. The algorithms have been implemented and tested on the problem of automatic shape extraction from feature points in image sequences.
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