Color image segmentation based on multi-level Tsallis–Havrda–Charvát entropy and 2D histogram using PSO algorithms
Introduction
Image segmentation is a process in which an image is partitioned into non-overlapping regions such that each region is homogeneous and two arbitrary adjacent regions are heterogeneous. Thresholding method is one of the simplest and the most widely used segmentation techniques. Basically, there are two types of thresholding methods: bi-level and multi-level thresholding. Bi-level thresholding methods [1], [2], [3], [4], [5], [6], [7], [8] assume that the image has only two homogeneous regions: object and background. However, in many applications, one encounters images with multiple regions. In the past ten years, different kinds of multi-level thresholding methods and algorithms have been proposed [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19].
One-dimensional (1D) histogram has been used as a thresholding technique for years. It is derived from the gray level information of each pixel, but does not take into account the spatial correlation between a pixel and its neighbor pixels. In order to overcome this drawback, people presented several types of two-dimensional histograms (2D) in the past few years. The first thresholding model based on 2D histogram and Shannon entropy was introduced in 1989 [4]. This 2D histogram was constructed by using the gray level of each pixel and the average gray level from the local neighborhood of the pixel, and named as the gray-level & local-average histogram (GLLA). In the recent few years, several thresholding models by applying other types of 2D histograms, such as, gray-level & local-variance histogram (GLLV) [20], gray-level & local-entropy histogram (GLLE) [21], gray-level & spatial-correlation histogram (GLSC) [22], [23], gray-level & gradient-magnitude histogram (GLGM) [24] and 2D direction histogram (2DD) [25] and so on were developed. In this paper, we mainly apply GLLA histogram to build the proposed model. In general, thresholding methods based on 2D histogram [4], [6], [7], [11], [12], [17], [18], [19] perform better than the 1D histogram methods [3], [5], [8], [13], [14], [15], [16].
Recently, entropic thresholding techniques have attracted more and more attention [3], [4], [5], [6], [7], [8], [12], [13], [14], [15], [16], [17], [18], [19]. An entropic thresholding model is mostly about searching for the optimal threshold values by maximizing or minimizing a criterion function. In 2004 de Albuquerque et al. [5], a 1D bi-level thresholding model was presented based on the non-extensive property of the Tsallis entropy. In the same year, Sahoo and Arora [6] proposed a Rényi entropic bi-level thresholding method by using GLLA histogram. In 2006 [7], they combined the GLLA histogram with the Tsallis–Havrda–Charvát entropy, and proposed a Tsallis–Havrda–Charvát entropic bi-level thresholding model. As for the multi-level thresholding, formulating the multi-level criterion function based on 1D Shannon entropy [14] is not a difficult task because of the extensive property of Shannon entropy. But it is not easy to formulate the multi-level criterion function based on Tsallis entropy. Sparavigna [13], in 2015, formulated a multi-level thresholding model based on 1D Tsallis entropy. Furthermore, in 2017, Ishak [17], [18] presented two multi-level thresholding models based on GLLA histogram by using Rényi entropy and Tsallis entropy respectively. We point out that, in 2016, a multi-level thresholding model based on GLLA histogram and Kullback–Leibler divergence, instead of entropy, was developed in [11]. However, all the thresholding models mentioned above didnot deal with color image segmentation. In this paper, we extend the multi-level thresholding technique to RGB color image.
Generally speaking, in our real world, a color image provides better description of a scene than the gray-level image [1], [2], [3], [9], [10], [19], [26]. It is known that most of the segmentation methods for a gray-level image can be directly applied to each component of a RGB color image [26]. However, so far only a limited amount of the studies [10], [19] mentioned how to employ the multi-level thresholding techniques on a color image. The discussions above give us a motivation to come up with a RGB color image segmentation model under the framework of a multi-level thresholding technique by using Tsallis–Havrda–Charvát entropy and GLLA histogram.
It is pointed out that most of the bi-level thresholding methods can be extended to multi-level with some appropriate modifications. But, as for the 2D multi-level extension, it gives rise to the exponential increase of computational time [6], since exhaustively searching for the optimal threshold values of a multi-level thresholding is an NP-hard combinatorial optimization problem [17]. In order to reduce the computational time, in recent years, people have been focusing on the metaheuristic algorithms, such as, Artificial Bee Colony (ABC) approach [16], Differential Evolution (DE) approach [12], Quantum Genetic (QG) algorithm [17] and Particle Swarm Optimization (PSO) algorithm [11], [13], [14], [15], [27]. In this paper, we implement all the experiments by applying PSO algorithm because of its simplicity in concept, time efficiency and highly convergent properties.
We test our method on The Berkeley Segmentation Dataset and Benchmark (BSDS300) extensively by computing the average four performance indices (Probability Rand Index, PRI, Global Consistency Error, GCE, Variation of Information, VOI and Boundary Displacement Error, BDE). In this paper, we compare the average four performance indices from the proposed model with the results from [11], [13], [17] to illustrate the effectiveness and reasonability of our proposed model.
The main contributions of this paper are as follows:
- (1)
We derive the generalized multi-level thresholding criterion function based on GLLA histogram and Tsallis–Havrda–Charvát entropy and validate this formulation rigorously by applying the mathematical induction method.
- (2)
We propose a multi-level thresholding scheme for RGB color image which is the first attempt that has been done so far according to our research. We assign the mean values from each thresholded class to obtain three segmented component images independently. Then, we obtain a segmented RGB color image which is very close to the original image and has fewer color levels than the original image.
- (3)
We demonstrate the dynamic idea of PSO algorithm by using a figure and employ the PSO algorithm to seek the optimal threshold values in a very reasonable computational time.
- (4)
We compare the labeled segmented image with the benchmark images (ground truth, human segmentation) from BSDS300 to evaluate the proposed model quantitatively and objectively. We calculate the average four performance indices (PRI, GCE, VOI and BDE) of the proposed model and compare them with the results from [11], [13], [17].
This paper is organized as follows: In Section 2, we discuss the background knowledge about the GLLA histogram, Tsallis–Havrda–Charvát entropy and PSO method respectively. In Section 3, we formulate the multi-level thresholding criterion function for the proposed model and validate the formulation by using the mathematical induction method. Then we present a thresholding scheme for RGB color image. In Section 4, we report the effectiveness of our model by applying the PSO algorithm on BSDS300 and calculating the four performance indices. In Section 5, we present some concluding remarks and future work from our model.
Section snippets
Background materials
In this section, the details of the GLLA histogram, Tsallis–Havrda–Charvát entropy and PSO algorithm are discussed.
Assume that a gray-level image is a function f(x, y): where for M ≥ 2 and . Then a RGB color image is a vector function such that:where fr(x, y), fg(x, y), fb(x, y) are red, green and blue components whose mixture generates any color that can be displayed. We use fc(x, y) to represent an
The proposed model
In this section, we formulate the multi-level thresholding criterion function based on Tsallis–Havrda–Charvát entropy and GLLA histogram and justify this formulation by using the mathematical induction method. Then, we extend the model to each color component of a RGB image to obtain three thresholded components and a segmented color image.
Experiments
In this section, we discuss how to use PSO algorithm to search the optimal thresholds. Next we illustrate how to conduct all the experiments on the images from Berkeley Segmentation Dataset (BSDS300) and compare the average four performance indices (PRI, GCE, VOI and BDE) of our model with the result from 2D K-L divergence model [11], 1D Tsallis-based model [13] and 2D Rényi-based model [17].
Conclusion and future work
In this paper, we develop a multi-level RGB color image thresholding algorithm based on Tsallis–Havrda–Charvát entropy of degree α and GLLA histogram. We apply the PSO algorithm to obtain the better performance results from our proposed model compared with 1D Tsallis-based model [13], 2D K-L divergence model [11] and 2D Rényi-based model [17] (see the discussion from Section 4). Actually, the Tsallis–Havrda–Charvát entropy, (see Eq. (3)), becomes Shannon entropy, S(p), when the degree α
Surina Borjigin graduated from the department of mathematics, University of Louisville, KY, USA with a Ph.D. in Applied & Industrial Mathematics in August 2018; M.A. in Mathematics, University of Louisville in May 2014; M.S. in Mathematics, Beihang University, Beijing, China in January 2012; B.S. in Information and Computer Science, Inner Mongolia University, Inner Mongolia, China in July 2007. Her research interest field is image segmentation and image thresholding.
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Surina Borjigin graduated from the department of mathematics, University of Louisville, KY, USA with a Ph.D. in Applied & Industrial Mathematics in August 2018; M.A. in Mathematics, University of Louisville in May 2014; M.S. in Mathematics, Beihang University, Beijing, China in January 2012; B.S. in Information and Computer Science, Inner Mongolia University, Inner Mongolia, China in July 2007. Her research interest field is image segmentation and image thresholding.
Prasanna K. Sahoo who used to be a professor in the department of mathematics, University of Louisville. He passed away on 6/18/2017.
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Deceased June 18, 2017.