Digital processing of speech signals

Calibration between color camera and 3D Light Detection And Ranging (LIDAR) equipment is an essential process for data fusion. The goal of this paper is to improve the calibration accuracy between a camera and a 3D LIDAR. In particular, we are interested in calibrating a low resolution 3D LIDAR with a relatively small number of vertical sensors. Our goal is achieved by employing a new methodology for the calibration board, which exploits 2D-3D correspondences. The 3D corresponding points are estimated from the scanned laser points on the polygonal planar board with adjacent sides. Since the lengths of adjacent sides are known, we can estimate the vertices of the board as a meeting point of two projected sides of the polygonal board. The estimated vertices from the range data and those detected from the color image serve as the corresponding points for the calibration. Experiments using a low-resolution LIDAR with 32 sensors show robust results.

Calibration between Color Camera and 3D LIDAR Instruments with a Polygonal Planar Board

Accurate segmentation of cervical cells in Pap smear images is an important step in automatic pre-cancer identification in the uterine cervix. One of the major segmentation challenges is overlapping of cytoplasm, which has not been well-addressed in previous studies. To tackle the overlapping issue, this paper proposes a learning-based method with robust shape priors to segment individual cell in Pap smear images to support automatic monitoring of changes in cells, which is a vital prerequisite of early detection of cervical cancer. We define this splitting problem as a discrete labeling task for multiple cells with a suitable cost function. The labeling results are then fed into our dynamic multi-template deformation model for further boundary refinement. Multi-scale deep convolutional networks are adopted to learn the diverse cell appearance features. We also incorporated high-level shape information to guide segmentation where cell boundary might be weak or lost due to cell overlapping. An evaluation carried out using two different datasets demonstrates the superiority of our proposed method over the state-of-the-art methods in terms of segmentation accuracy.

Accurate Cervical Cell Segmentation from Overlapping Clumps in Pap Smear Images

This paper reports on an algorithm for automatic, targetless, extrinsic calibration of a lidar and optical camera system based upon the maximization of mutual information between the sensor-measured surface intensities. The proposed method is completely data-driven and does not require any fiducial calibration targets-making in situ calibration easy. We calculate the Cramer-Rao lower bound CRLB of the estimated calibration parameter variance, and we show experimentally that the sample variance of the estimated parameters empirically approaches the CRLB when the amount of data used for calibration is sufficiently large. Furthermore, we compare the calibration results to independent ground-truth where available and observe that the mean error empirically approaches zero as the amount of data used for calibration is increased, thereby suggesting that the proposed estimator is a minimum variance unbiased estimate of the calibration parameters. Experimental results are presented for three different lidar-camera systems: i a three-dimensional 3D lidar and omnidirectional camera, ii a 3D time-of-flight sensor and monocular camera, and iii a 2D lidar and monocular camera.

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Automatic Extrinsic Calibration of Vision and Lidar by Maximizing Mutual Information

This paper presents a new algorithm for the extrinsic calibration of a perspective camera and an invisible 2D laser-rangefinder (LRF). The calibration is achieved by freely moving a checkerboard pattern in order to obtain plane poses in camera coordinates and depth readings in the LRF reference frame. The problem of estimating the rigid displacement between the two sensors is formulated as one of registering a set of planes and lines in the 3D space. It is proven for the first time that the alignment of three plane-line correspondences has at most eight solutions that can be determined by solving a standard p3p problem and a linear system of equations. This leads to a minimal closed-form solution for the extrinsic calibration that can be used as hypothesis generator in a RANSAC paradigm. Our calibration approach is validated through simulation and real experiments that show the superiority with respect to the current state-of-the-art method requiring a minimum of five input planes.

A Minimal Solution for the Extrinsic Calibration of a Camera and a Laser-Rangefinder

This paper presents an effective algorithm for calibrating the extrinsic parameters between a camera and a laser range finder whose trace is invisible. On the basis of an analysis of three possible features, we propose to design a right-angled triangular checkerboard and to employ the invisible intersection points of the laser range finder's slice plane with the edges of the checkerboard to set up the constraints equations. The extrinsic parameters are then calibrated by minimizing the algebraic errors between the measured intersections points and their corresponding projections on the image plane of the camera. We compared our algorithm with the existing methods by both simulations and the real data of a stereo measurement system. The simulation and experimental results confirmed that the proposed algorithm can yield more accurate results.

An algorithm for extrinsic parameters calibration of a camera and a laser range finder using line features

Overlapping cells segmentation is one of the challenging topics in medical image processing. In this paper, we propose to approximately represent the cell contour as a set of sparse contour points, which can be further partitioned into two parts: the strong contour points and the weak contour points. We consider the cell contour extraction as a contour points locating problem and propose an effective and robust framework for segmentation of partially overlapping cells in cervical smear images. First, the cell nucleus and the background are extracted by a morphological filtering-based K-means clustering algorithm. Second, a gradient decomposition-based edge enhancement method is developed for enhancing the true edges belonging to the center cell. Then, a dynamic sparse contour searching algorithm is proposed to gradually locate the weak contour points in the cell overlapping regions based on the strong contour points. This algorithm involves the least squares estimation and a dynamic searching principle, and is thus effective to cope with the cell overlapping problem. Using the located contour points, the Gradient Vector Flow Snake model is finally employed to extract the accurate cell contour. Experiments have been performed on two cervical smear image datasets containing both single cells and partially overlapping cells. The high accuracy of the cell contour extraction result validates the effectiveness of the proposed method.

Accurate Segmentation of Partially Overlapping Cervical Cells Based on Dynamic Sparse Contour Searching and GVF Snake Model

Tuberculosis (TB) is a communicable disease for which early diagnosis is critical for disease control. Manual screening for TB identification involves a labor-intensive task with poor sensitivity and specificity. To improve the diagnostic process we develop an automated system for TB identification, which consists of an automatic microscope, an image-based autofocus algorithm and an image-based TB identification algorithm. The system can automatically capture a large number of clear images on sputum sample and process all the images in real time to identify the bacilli and count their number. In order to speed up image acquisition while guaranteeing the image quality, an efficient method for capturing the images is proposed. To obtain fine segmentation results, a two-stage segmentation method based on both the HSV and CIE L*a*b* color space is developed. To identify the TB bacilli, the algorithm uses three shape feature descriptors, which are area, compactness and roughness, and makes the judgment using a decision tree. Experimental results confirmed the superior performance of the proposed algorithm.

Automatic identification of mycobacterium tuberculosis from ZN-stained sputum smear: Algorithm and system design

This paper presents a new 3D reconstruction method using feature points extracted by the SIFT and Harris corner detector. Since the SIFT feature points can be detected stably and relatively accurately, the proposed algorithm first uses the SIFT matching points to calculate the fundamental matrix. On the other hand many of the feature points detected by the SIFT are not what we need for reconstruction, so by combining the SIFT feature points with the Harris corners it is possible to obtain more vivid and detailed 3D information. Experiments have been conducted to validate the proposed method.

3D reconstruction based on SIFT and Harris feature points

Corner detection has been shown to be extremely useful in many computer vision applications. In this paper, an improved SUSAN corner detector is proposed and its performance is compared with Harris and SUSAN corner detection. The method adopts an adaptive multi-threshold strategy based on local brightness rather than one threshold for the whole image, and divides the circular mask area of SUSAN into two or more parts. Next, the number of pixels in the part where the nucleus locates is calculated. If the number is less than half the total pixels of the circular mask, the nucleus becomes a corner candidate. The exact positions of image corners are those candidates with local minimum numbers. In order to improve the computational efficiency of the algorithm, we limit the search space for corner candidates to those pixels whose intensity gradient magnitudes by Sobel operator are higher than a threshold. Experiments have demonstrated that our corner detector is accurate and efficient.

Dongxiang Zhou

Papers

An algorithm for extrinsic parameters calibration of a camera and a laser range finder using line features

Accurate Segmentation of Partially Overlapping Cervical Cells Based on Dynamic Sparse Contour Searching and GVF Snake Model

Automatic identification of mycobacterium tuberculosis from ZN-stained sputum smear: Algorithm and system design

3D reconstruction based on SIFT and Harris feature points

An efficient and robust corner detection algorithm