A hybrid level set model for image segmentation

Local image information is crucial for accurate segmentation of images with intensity inhomogeneity. However, image information in local region is not embedded in popular region-based active contour models, such as the piecewise constant models. In this paper, we propose a region-based active contour model that is able to utilize image information in local regions. The major contribution of this paper is the introduction of a local binary fitting energy with a kernel function, which enables the extraction of accurate local image information. Therefore, our model can be used to segment images with intensity inhomogeneity, which overcomes the limitation of piecewise constant models. Comparisons with other major region-based models, such as the piece-wise smooth model, show the advantages of our method in terms of computational efficiency and accuracy. In addition, the proposed method has promising application to image denoising.

Image segmentation actually could be regarded as a computer vision pre-processing step of cloud computing and big data analysis. Active contour model is a new research direction for images segmentation in synthetic aperture radar(SAR) images. However, due to the SAR images have speckle noise and low signal-to-clutter ratio, active contour models cannot produce satisfied segmentation results. To solve these issues, active contours driven by visual saliency fitting energy is proposed in this paper. First, a saliency map is calculated by improved local contrast measure. Then, a visual saliency fitting energy is proposed based on saliency map and local binary fitting energy. The saliency map has a higher signal-to-clutter ratio and the local binary fitting energy is an active contour model that can effectively segment images with intensity inhomogeneity. In this way, the proposed method has a better segmentation result. The experiments on ship chips in SAR images demonstrate that the proposed method is robust to speckle noise and the segmentation result has good connectivity and integrity for entire ship targets.

Active contour models are always designed on the assumption that images are approximated by regions with piecewise-constant intensities. This assumption, however, cannot be satisfied when describing intensity inhomogeneous images which frequently occur in real world images and induced considerable difficulties in image segmentation. A milder assumption that the image is statistically homogeneous within different local regions may better suit real world images. By taking local image information into consideration, an enhanced active contour model is proposed to overcome difficulties caused by intensity inhomogeneity. In addition, according to curve evolution theory, only the region near contour boundaries is supposed to be evolved in each iteration. We try to detect the regions near contour boundaries adaptively for satisfying the requirement of curve evolution theory. In the proposed method, pixels within a selected region near contour boundaries have the opportunity to be updated in each iteration, which enables the contour to be evolved gradually. Experimental results on synthetic and real world images demonstrate the advantages of the proposed model when dealing with intensity inhomogeneity images.

This study presents an efficient variational region-based active contour model for segmenting images without priori knowledge about the object or background. In order to handle intensity inhomogeneities and noise, we propose to integrate into the region-based local intensity model a global density distance inspired by the Bhattacharyya flow. The local term based on local information of segmented image allows the model to deal with bias field artifact, which arises in data acquisition processes. The global term, which is based on the density distance between the probability distribution functions of image intensity inside and outside the active contour, provides information for accurate segmentation, keeps the curve from spilling, and addresses noise in the image. Intensive 2D and 3D experiments on many imaging modalities of medical fields such as computed tomography, magnetic resonance imaging, and ultrasound images demonstrate the effectiveness of the model when dealing with images with blurred object boundary, intensity inhomogeneities, and noise.

The local intensity fitting active contour models can handle inhomogeneous images, but they suffer from the shortcomings of poor performance in segmenting images with severe intensity inhomogeneity and being sensitive to initializations. To overcome these problems, we put forward a robust active contour model by introducing two adjustment coefficient functions. The energy functional of the proposed model is presented by integrating the local fitting term and two adjustment coefficient functions. The local fitting term is defined by introducing two local fitting functions that approximate the image intensities inside and outside of the contour. These two adjustment coefficient functions, which improve the segmentation performance and enhance the robustness to initialization, are constructed by utilizing the Sigmoid function as well as the difference between local intensity averages and image actual intensities. The results of the experiments on synthetic and real images demonstrate that the presented model not only is capable of handling intensity inhomogeneity better under more flexible initializations but also takes less time in comparison with other region-based models. Furthermore, these two adjustment coefficients can be employed to other local intensity fitting models to enhance the robustness to initialization and to decrease the segmentation time.

An algorithm is proposed, which combines global and local information of fingerprint images to detect singular points. It’s mathematically proven that normal lines of gradient of double orientation field(GDOF) pass through singular points. Normal lines of GDOF use rather global information to detect candidate singular points. Fingerprint image is divided into blocks and normal lines of GDOF are drawn. The number of normal lines that pass through each block is accumulated. The block that has the maximum number corresponds to a candidate singular point. It can be seen as a kind of Hough transform(HT). As candidate singular points detected by global information may have a little warp from their real positions, it’s necessary to use local information to refine their positions. Poincare index is chosen, and uses local information to refine the candidate singular points. This makes our algorithm more robust to noise than methods that only use local information. What’s more, the pairs of the detected singular points are used to classify fingerprint. Experimental results show that our algorithm performs well and fast enough for real time application in databases NIST-4.

Lumen segmentation of the carotid artery is an important preprocessing step with clinical application, because it facilitates subsequent analysis, including stenosis grading, the detection and quantification of plaque components in the vessel wall. But it is a challenging task owing to the low and varying contrast between the surrounding tissues. Plus, intensity inhomogeneity often occurs in medical images from different modalities, which causes undesirable side effects when the traditional Chan-Vese (CV) model is applied. In order to overcome the intensity inhomogeneity problem we improve the CV model by adding a local fitting term, which incorporates both local information and global information. We also introduce a penalizing energy to avoid the time-consuming re-initialization procedure in traditional level set method.We propose and validate a semi-automatic method for lumen segmentation of carotid artery in computed tomography angiography(CTA). First we manually select a seedpoint on the lumen area, then the segmentation is automatically obtained using a level set. By combining both global and local statistical information, we manage to overcome the inhomogeneous intensity distribution in the CTA images and provide more satisfying segmentation result than CV model. Experiments on carotid artery CTA data have demonstrated the efficiency and accuracy of our model, in addition our model is also less sensitive to the location of the initial contour. Therefore our method has the potential to replace the manual procedure of lumen segmentation in CTA, which is of great value for doctors with clinical applications.

Active contours driven by local likelihood image fitting energy for image segmentation

We investigated a parametric kernel-driven active contour (PKAC) model, which implicitly transfers kernel mapping and piecewise constant to modeling the image data via kernel function. The proposed model consists of curve evolution functional with three terms: global kernel-driven and local kernel-driven terms, which evaluate the deviation of the mapped image data within each region from the piecewise constant model, and a regularization term expressed as the length of the evolution curves. In the local kernel-driven term, the proposed model can effectively segment images with intensity inhomogeneity by incorporating the local image information. By balancing the weight between the global kernel-driven term and the local kernel-driven term, the proposed model can segment the images with either intensity homogeneity or intensity inhomogeneity. To ensure the smoothness of the level set function and reduce the computational cost, the distance regularizing term is applied to penalize the deviation of the level set function and eliminate the requirement of re-initialization. Compared with the local image fitting model and local binary fitting model, experimental results show the advantages of the proposed method in terms of computational efficiency and accuracy.

Integrating local distribution information with level set for boundary extraction

The segmentation and detection of various types of nodules in a Computer-aided detection (CAD) system present various challenges, especially when (1) the nodule is connected to a vessel and they have very similar intensities; (2) the nodule with ground-glass opacity (GGO) characteristic possesses typical weak edges and intensity inhomogeneity, and hence it is difficult to define the boundaries. Traditional segmentation methods may cause problems of boundary leakage and “weak” local minima. This paper deals with the above mentioned problems. An improved detection method which combines a fuzzy integrated active contour model (FIACM)-based segmentation method, a segmentation refinement method based on Parametric Mixture Model (PMM) of juxta-vascular nodules, and a knowledge-based C-SVM (Cost-sensitive Support Vector Machines) classifier, is proposed for detecting various types of pulmonary nodules in computerized tomography (CT) images. Our approach has several novel aspects: (1) In the proposed FIACM model, edge and local region information is incorporated. The fuzzy energy is used as the motivation power for the evolution of the active contour. (2) A hybrid PMM Model of juxta-vascular nodules combining appearance and geometric information is constructed for segmentation refinement of juxta-vascular nodules. Experimental results of detection for pulmonary nodules show desirable performances of the proposed method.

Uncertain active contour model based on rough and fuzzy sets for auroral oval segmentation

This study proposes an innovative approach for the recycling of dry wastewater sludge in the production of fired clay bricks, aiming to create environmentally friendly and cost-effective building materials. Consequently, the proposed research focuses on optimizing the thermal and mechanical properties of ceramic bricks, while incorporating sewage sludge as a pore-forming agent in brick manufacturing process. For the assessment of porosity in ceramic brick mixtures with varying volumetric proportions of ash, clay and wastewater sludge, a novel method for microscopy image analysis is proposed. This advanced image segmentation method uses active contours driven by local image information to accurately estimate brick porosity from light microscopy images, coping with light reflections, intensity inhomogeneity, and the defocus effect present on the sample surface. The thermal properties of the ceramic blocks were assessed using non-contact infrared lock-in thermography and thermogravimetric analysis (TGA). The obtained results indicate that incorporating sewage sludge increases porosity, thereby improving the material's insulating properties, with the cost of reduced mechanical strength. Nevertheless, the compressive strength for a mixture containing 15% of sewage sludge meets the criteria for the production of first-class bricks, according to ASTM C62 standards for brick manufacturing. The present study demonstrates that incorporating sewage sludge into fired clay ceramic bricks production is a feasible and sustainable approach, offering significant advantages for waste management and promoting energy-efficient building design.

C-V model has the advantage of being able to detect boundaries of objects that are not defined by gradient. However, when detecting these types of edges, the C-V model only considers the average value of each region without local information. As a result, its segmentation result may exist errors, when detecting non-gradient defined boundaries. In order to overcome this problem, we modify the fitting term of classical C-V model with an extra weight. This weight can control the relative height of zero-level contour, so the new method can decrease the segmentation errors. Experiments show that the new model can obtain more accurate results and segment multi-phase images by setting proper weights. Active contour models (1), based on level set method, are one important type of methods in image segmentation. Those methods can handle topological changes automatically, and can get the boundaries of objects with complex edges. At present, there are two categories of active contour methods. One is based on the edge information and the other is based on the region information. Snakes (2), geometric active contours (3), geodesic active contours (GAC) model (4) are edge-based models. These methods get the boundaries of objects from the gradients of images. As these methods depend on the gradient information, when processing images with non-gradient defined edges, they will get wrong boundaries. While M-S model (5) and C-V model (6) are based on global region information. They take piecewise constant patches as the solution of segmentation problems. As a result, it can process the images whose edges are not well defined. Additionally, C-V model can process images fast and segment the objects with inner-boundaries, and its solution is robust to the initialization of the curves. However, C-V model may have problems when detecting blurred and fuzzy edges. The reason is that the C-V model only considers the averages inside and outside the zero-level contours, and the results determined by its energy functional may be not suitable for these edge types. In this paper, we propose an improved C-V model with a generalized fitting term to deal with the above problem. A weight factor w added into the generalized fitting term, controls the height of zero-level sets of the original C-V model. Thus we may obtain accurate segmentation results by

A novel image segmentation algorithm based on the adaptive edge detection and an improved mean shift is proposed. According to the Ostu method, an adaptive threshold algorithm is applied to improve Canny operator in edge detection. The edge detection method has better performance and strong adaptability. Then the resulting edge information is incorporated into the main two steps of image segmentation based on mean shift. Since the discontinuity and homogeneity information are combined flexibly, the proposed algorithm takes the best of local and global image information. Experimental results reveal that the proposed algorithm is stronger adaptive and achieves better segmentation performance compared with several typical kinds of methods.