A top-down region dividing approach for image segmentation
Introduction
Image segmentation aims to extract or threshold objects with respect to the background. It is a critical preprocessing step to the success of image recognition [1], image compression [2], image visualization [3], and image retrieval [4]. There are many types of image segmentation techniques [2], [3], [4], [5], [6], [7]. Among them, the histogram-based and the region-based algorithms are most popular.
The histogram-based (or feature-based) segmentation technique produces a binary image based on the threshold value [6]. The intensities of object and background pixels tend to cluster into two sets in the histogram. The histogram will be bimodal by a threshold value, which is selected from the valley between the two sets. The optimal segmentation intends to find the threshold value that minimizes the misclassification. If the threshold is too high, many object pixels will be lost and object contour will be severely destroyed. Although the complexity of histogram-based technique is low, the threshold selection is difficult, especially when the histogram is multi-modal. Furthermore, the histogram-based technique only considers the feature image (histogram) without checking the spatial relationship among connected pixels.
Watershed-based segmentation, a region-based approach, uses a bottom-up strategy that segments an image into several small regions, followed by a merge procedure. The immersion-based system [8] and the drainage rainfall system [9] are two approaches for performing watershed transformation. It considers an image as a topographic surface and the image intensity as the altitude. The drop of water will progressively fill up the ascending catchment basins from the minima of lowest altitude (lowest intensity) of the surface. Each pixel will flow along a descending path to a local minimum. When the altitude of water gradually increases, two catchment basins will reach at some points, called watershed points. A collection of watershed pixels on the contour is defined as the watershed line. Since the watershed algorithm is highly sensitive to the local minimum, it usually results in over-segmentation. In other words, there are overcrowded regions segmented in an image. Furthermore, in order to merge similarly smaller connected regions, the region adjacency graph (RAG) is used for region growing. Although the watershed-based image segmentation provides better results than the histogram-based approach, its computational complexity is high.
In order to provide more efficient algorithms that not only obtain better results, but also maintain low complexity, a novel top-down region dividing (TDRD) based approach is developed to iteratively divide sub-regions if the size of a sub-region is larger than a predefined threshold or the homogeneity of a sub-region is larger than a predefined threshold. The rest of this paper is organized as follows. In Section 2, we present the overview of the proposed TDRD-based image segmentation. The region dividing and sub-region examination strategies are provided in Section 3. Experimental results are shown in Section 4. Section 5 introduces its potential applications to medical image analysis. Finally, conclusions are drawn in Section 6.
Section snippets
Problem motivation
The histogram-based image segmentation method, although its complexity is low, does not consider the spatial relationship of neighborhood and may fail in some cases, such as the case in Fig. 1. Fig. 1(a) shows an image containing dark and bright parts on the left and right areas, respectively. In each part, gray values gradually increase from left to right. For example, the pixels on the leftmost column of left part are “32,” and are increased by 1 on each column to the right, until the pixels
Region dividing procedure
The region dividing procedure is based on our previous image simplification algorithm [10] that combines the advantages from histogram-based and region-based segmentation methods. It includes three steps: (a) suspicious intensities determination, (b) suspicious pixels determination, and (c) final intensity determination (FID).
(a) Suspicious intensities determination: The suspicious intensities are determined by comparing the histograms of two transformed images using histogram equalization
Experimental results
We perform our algorithm using two dividing iterations on an input image in Fig. 5(a). After obtaining Fig. 8(a) which performs one dividing iteration, we continuously segment all the sub-regions to achieve two dividing iterations for an input image. The results of performing the second iteration of our TDRD-based image simplification are shown in Fig. 9. Since there are three classes in white, gray and black in Fig. 8(a), the results of the second iteration are shown below for each class.
- (1)
Figs.
Potential applications in medical image analysis
Medical image analysis is important since it provides assistance for medical doctors to find out the diseases inside the body without the surgery procedure [15]. The TDRD-based image segmentation provides useful applications due to the properties of medical images. Generally, medical images contain three major regions: background, soft tissue, and object. We present the ideas of two potential applications, breast boundary segmentation and lung segmentation. Further detailed implementation is
Conclusions
We have presented a TDRD-based image segmentation technique to combine the advantages of histogram-based and region-based approaches. The TDRD-based algorithm consists of two major procedures: region dividing and sub-region evaluation. In the region dividing procedure, the suspicious pixels are obtained from the suspicious intensities. In the sub-region evaluation procedure, the final intensities of suspicious pixels are determined by considering local spatial information. Experimental results
About the Author—YI-TA WU was born in Taipei, Taiwan. He received the B.S. degree in Physics from Tamkang University, Taipei, Taiwan, in 1995, and the M.S. degree in Computer Science from National Dong-Hwa University, Hualien, Taiwan, in 1997. Dr. Wu received Ph.D. from Department of Computer Science, New Jersey Institute of Technology, in May 2005. He is now a research fellow at University of Michigan, Ann Arbor. His current research interests include image/video processing, mathematical
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About the Author—YI-TA WU was born in Taipei, Taiwan. He received the B.S. degree in Physics from Tamkang University, Taipei, Taiwan, in 1995, and the M.S. degree in Computer Science from National Dong-Hwa University, Hualien, Taiwan, in 1997. Dr. Wu received Ph.D. from Department of Computer Science, New Jersey Institute of Technology, in May 2005. He is now a research fellow at University of Michigan, Ann Arbor. His current research interests include image/video processing, mathematical morphology, image watermarking, steganography, surveillance system, robot vision, pattern recognition, shortest path planning, and artificial intelligence.
About the Author—FRANK Y. SHIH received the B.S. degree from National Cheng-Kung University, Taiwan, in 1980, the M.S. degree from the State University of New York at Stony Brook, in 1984, and the Ph.D. from Purdue University, West Lafayette, Indiana, in 1987, all in Electrical Engineering. He is presently a professor jointly appointed in the Department of Computer Science, the Department of Electrical and Computer Engineering, and the Department of Biomedical Engineering at New Jersey Institute of Technology, Newark, NJ. He currently serves as the Director of Computer Vision Laboratory.
Dr. Shih is currently on the Editorial Board of the International Journal of Pattern Recognition, the International Journal of Pattern Recognition Letters, the International Journal of Pattern Recognition and Artificial Intelligence, the International Journal of Recent Patents on Engineering, the International Journal of Recent Patents on Computer Science, the International Journal of Internet Protocol Technology, and the Journal of Internet Technology. Dr. Shih has contributed as a steering member, committee member, and session chair for numerous professional conferences and workshops. He was the recipient of the Research Initiation Award from the National Science Foundation in 1991. He won the Honorable Mention Award from the International Pattern Recognition Society for Outstanding Paper and also won the Best Paper Award in the International Symposium on Multimedia Information Processing. He has received several awards for distinguished research at New Jersey Institute of Technology. He has served several times on the Proposal Review Panel of the National Science Foundation.
Dr. Shih holds the research fellow for the American Biographical Institute and the IEEE senior membership. He has published seven book chapters and over 180 technical papers, including 85 in well-known prestigious journals. His current research interests include image processing, computer vision, sensor networks, pattern recognition, bioinformatics, information security, robotics, fuzzy logic, and neural networks.
About the Author—JIAZHENG SHI received B.E. and M.E. from Beijing University of Posts & Telecom, respectively, in 1997 and 2000, and received Ph.D. from University of Nebraska-Lincoln in 2005. He is now a research fellow at University of Michigan, Ann Arbor. His research interests include image processing and medical imaging analysis.