INTERNATIONAL JOURNAL OF RESEARCH IN COMPUTER APPLICATIONS AND ROBOTICS ISSN

INTERNATIONAL JOURNAL OF RESEARCH IN COMPUTER APPLICATIONS AND ROBOTICS ISSN 2320-7345 IMAGE DENOISING TECHNIQUES FOR SALT AND PEPPER NOISE., A COMPARATIVE STUDY Bibekananda Jena 1, Punyaban Patel 2, Banshidhar Majhi 3, C.R.Tripathy 4 1 Department of ETE, 2 Department of IT, 3,4 Department of CSE e-mail: 1,2 Purushottam Institute of Engineering and Technology, Rourkela, India 3 National Institute of Technology Rourkela, India 4 VSSUT, Burla, India 1 bibekananda.jena@gmail.com, 2 punyaban@gmail.com, bmnitr@gmail.com, 3 crt.vssut@yahoo.com Abstract Noise present in the image hides necessary details. It compromises with level of quality of image. So, it needs to remove the noise from images. We briefly describe and compare some recent advances in image denoising schemes. In particular, we discuss eight leading denoising algorithms, and describe their similarities and differences in terms of both structure and performance. With the help of these experiments, we are able to identify the strengths and weaknesses of these state of the art methods, as well as seek the way ahead towards a definitive solution to the longstanding problem of image denoising. In this paper, we make a survey on various denoising filters and conclude which works better among all. Keywords Image De-noising, Spatial Filters, Median Filters, Peak Signal-to-Noise Ratio (PSNR), Structural Similarity Index Measure (SSIM). 1. Introduction Image Processing is a technique to enhance raw images received from cameras/sensors placed on satellites, space and aircrafts or pictures taken in normal day-to-day life for various applications. A digital image is an array of real numbers represented by a finite number of bits [1]. Denoising has been an important and long-standing problem in image processing for many decades. In the last few years, however, several strong contenders have emerged which produce stunning results across a wide range of image types, and for varied noise distributions, and strengths [1, 2]. In this paper, we do take a modest step in exposing the similarities, strengths, and weaknesses of these competing methods, paving the way for the resolution of the more fundamental questions in future work. The rest of this paper is organized as follows: in Section 2, the eight types of image denoising techniques are explained as a literature review, the noise model is explained in Section 3, performance measured in section 4, the simulation and result is discussed in section 5, and the conclusion in section 6. B i b e k a n a n d a J e n a e t a l Page 27

2. Literature Review In this section, we have gone through detail literature reviews of impulse noise removal on the reported recent articles and critically studied their performances through computer simulation described as below; [1, 2, 16]. In traditional median filtering called standard median filter (SMF) [3,4], the filtering operation is performed across to each pixel without considering whether it is uncorrupted. So, the image details, contributed by the uncorrupted pixels are also subjected to filtering and as a result the image details are lost in the restored version. To alleviate this problem, an impulse noise detection mechanism is applied prior to the image filtering. A Dynamic Adaptive Median Filter (DAMF) [5] was proposed for removing high density salt and pepper noise. The filter is dynamic in nature as it decides the window size for the test pixel locally before filtering during run time and is adaptive due to the selection of a proper window size. The progressive switching median filter (PSMF) [6] was proposed which achieves the detection and removal of impulse noise in two separate stages. In first stage, it applies impulse detector and then the noise filter is applied progressively in iterative manners in second stage. In this method, impulse pixels located in the middle of large noise blotches can also be properly detected and filtered. The performance of this method is not good for very highly corrupted image. Nonlinear filters such as adaptive median filter (AMF) [7] can be used for discriminating corrupted and uncorrupted pixels and then apply the filtering technique. Noisy pixels will be replaced by the median value, and uncorrupted pixels will be left unchanged. An efficient decision-based algorithm (DBA) [8] was proposed using a fixed window size of 3 3, where the corrupted pixels are replaced by either the median pixel or neighborhood pixels. It shows promising results, a smooth transition between the pixels is lost with lower processing time which degrades the visual quality of the image. A novel improved median filtering (NIMF) [9] algorithm is proposed for removal of highly corrupted with salt-and-pepper noise from images. Firstly all the pixels are classified into signal pixels and noisy pixels by using the Max-Min noise detector. The noisy pixels are then separated into three classes, which are low-density, moderatedensity, and high-density noises, based on the local statistic information. Finally, the weighted 8-neighborhood similarity function filter, the 5 5 median filter and the 4-neighborhood mean filter are adopted to remove the noises for the low, moderate and high level cases, respectively. A Tolerance based Arithmetic Mean Filtering Technique (TSAMFT) [10] is proposed to remove salt and pepper noise from corrupted images. Arithmetic Mean filtering technique is modified by the introduction of two additional features. In the first phase, to calculate the Arithmetic Mean, only the unaffected pixels are considered. In the second phase, a Tolerance value has been used for the replacement of the pixels. This proposed technique provides much better results than that of the existing mean and median filtering techniques. A modified decision based unsymmetrical trimmed median filter (MDBUTMF) [11] algorithm is proposed for the restoration of gray scale, and color images that are highly corrupted by salt and pepper noise. The proposed algorithm replaces the noisy pixel by trimmed median value when other pixel values, 0 s and 255 s are present in the selected window and when all the pixel values are 0 s and 255 s then the noise pixel is replaced by mean value of all the elements present in the selected window. When this algorithm tested against different gray scale and color images, it gives better Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM). 3. Noise Models Generally, image is affected by different types of noise. The most common types of noise encountered, in image are Impulse noise, Gaussian noise and the combination of both called mixed noise. Impulsive noise can be classified as salt-and-pepper noise (SPN) and random-valued impulse noise (RVIN)[1,2,3]. An image containing impulsive noise can be described as follows: η(i, j)with probability x(i, j) = p y(i, j)with probability 1 p (3.1) Where, x(i, j) denotes a noisy image pixel, y(i, j) denotes a noise free image pixel and η(i, j) denotes a noisy impulse at the location(i, j). In salt-and-pepper noise, noisy pixels take either minimal or maximal values B i b e k a n a n d a J e n a e t a l Page 28

i.e. η(i, j) {L, L }, and for random-valued impulse noise, noisy pixels take any value within the range minimal to maximal value i.e. y(i, j) [L, L ] where, L, L denote the lowest and the highest pixel luminance values within the dynamic range respectively. 4. Performance Measures One of the issues of de-noising is the measure of the reconstruction error. In order to separate the noise and image components from a single observation of a degraded image it is necessary to assume or have knowledge about the statistical properties of the noise. The metrics used for performance comparison of different filters (exists) are given below; [13,14]. (i) Peak Signal to Noise Ratio (PSNR) Given that original image X of size (M N) pixels and as reconstructed image X, the MSE is defined as: MSE = Similar, the PSNR (db) is defined as: (4.1) ( X, X, ) (ii) Structural Similarity Index Measure (SSIM) PSNR(dB) = 10 log (4.2) SSIM X, X = ( )( ) ( )( ) (4.3) μ and μ represent the mean of the original and restored images. σ and σ represent the standard deviation of the original and restored images. σ represent the co-standard deviation of the original and restored image. C and C represent small constant are added to avoid instability. 5. Simulations and Results. In this section, we compared the denoising performance of the methods introduced in the previous section. The performance of all these filters has been evaluated qualitatively and quantitatively through experimental analysis. The Peak Signal Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) are used to evaluate quality of the image after applying noise removal methods. Although extensive simulations were carried out using standard test images, only performance evaluation using images such as Lena image of size 512 512, and Boat image of size 512 512 are explained in this section. The images are subjected to as low as 10% noise density to as high as 90% noise density. Some standard and recently suggested few well performing schemes like SMF, PSMF, AMF, DBA, IDBA, NIMF, MDBUTMF and DAMF are applied to the noisy images. The simulation is carried out using MATLAB 7.0. Table-1 and 2 shows the PSNR and SSIM values of different filters for Boat images. The same are also plotted in Figure-1 and 2 for Lena image. From the result it is clear that DAMF has given excellent performance even if the noise density is too high. Even though the result of MDBUTMF and DAMF are works well up to 40% noise, MDBUTMF is failed to show better performance for high noise density because of using fixed window size in filtering. In order to give a visual impression about the performances of the filters included in the comparison, the results of test images Lena is given in Figure-3. It shows that, the most appealing visual result is produced by the DAMF filter. B i b e k a n a n d a J e n a e t a l Page 29

Table 1: Comparative results in PSNR(dB) of different filters for boat image corrupted with salt and pepper noise of varying strength Name of % of noise filters 10 20 30 40 50 60 70 80 90 SMF 30.5053 27.5743 22.8572 18.5194 15.0823 12.2046 9.8480 7.9985 6.4759 PSMF 33.4886 30.0736 27.4559 24.4729 22.9539 21.6866 18.7751 13.0581 7.5560 AMF 34.8437 32.0047 29.4418 27.1750 25.3635 24.1938 22.5625 20.7916 18.2041 DBA 35.2274 32.8400 30.6642 28.7420 27.1391 25.6242 23.9436 21.9022 19.3607 TSAMF 34.5989 31.4543 28.8550 26.5061 24.5939 22.7814 21.6897 19.9584 18.7151 NIMF 37.7004 34.5577 32.6481 31.2240 30.0527 28.9015 27.6643 26.1985 23.5982 MDBUTMF 40.0667 36.2844 33.8956 31.9350 29.8555 27.3214 23.5516 19.4438 15.3040 DAMF 39.9957 36.3133 33.8736 31.8377 30.2321 28.6669 27.2101 25.4505 23.4890 Table 2: Comparative results in SSIM of different filters for boat image corrupted with salt and pepper noise of varying strength Name of % of noise filters 10 20 30 40 50 60 70 80 90 SMF 0.9893 0.9792 0.9400 0.8482 0.7039 0.5232 0.3409 0.1920 0.0748 PSMF 0.9947 0.9886 0.9796 0.9604 0.9453 0.9294 0.8707 0.6158 0.1945 AMF 0.9961 0.9925 0.9865 0.9774 0.9658 0.9555 0.9355 0.9044 0.8317 DBA 0.9964 0.9938 0.9898 0.9841 0.9771 0.9675 0.9523 0.9240 0.8636 TSAMF 0.9959 0.9915 0.9843 0.9726 0.9560 0.9312 0.9099 0.8606 0.7880 NIMF 0.9980 0.9958 0.9935 0.9910 0.9882 0.9846 0.9796 0.9713 0.9479 MDUTMF 0.9980 0.9972 0.9951 0.9924 0.9876 0.9778 0.9470 0.8614 0.6218 DAMF 0.9988 0.9972 0.9951 0.9922 0.9887 0.9837 0.9771 0.9657 0.9456 Figure-1: PSNR characteristics for Lena image at various noise densities B i b e k a n a n d a J e n a e t a l Page 30

Figure-2: SSIM characteristics for Lena image at various noise densities % of Noise 30% (a) 50% (b) 70% (c) 90% (d) Methods Noisy Image (a) SMF (b) PSMF (c) AMF (d) Bibekananda Jena et al Page 31

DBA (e) NIMF (f) TSAMFT (g) MDBUTMF (h) DAMF (i) Figure 3 : Column a,b,c and d represents the Noisy and restored images of Lena image for 30%, 50%, 70% and 90% noise respectively. Rows a to i shows the Noisy image and Restored image of the SMF, PSMF, AMF, DBA, NIMF, TSAMFT, MDBUTMF abd DAMF techinques respectively. 6. Conclusion In this paper some standard and current method are discussed and compared for restoration of an image, corrupted by salt and pepper noise. For lower values of noise the standard filters like median filter and adaptive median filter can denoise salt and pepper noise, but fail to remove noise effectively as the noise density increase. The comparative study explained with help of PSNR and MSE. From the performance analyses the currently proposed DAMF algorithm outperforms the other denoising techniques at low as well as high noise density. References [1] R. C. Gonzalez and R. E. Woods, Digital Image Processing, Addison Wesley, 2nd edition, 1992, First Impression 2009. [2] S.Sridhar, Digital Image Processing, Oxford University Press, 2011. [3] Eng, H.-L., Ma, K.-K. Noise adaptive soft-switching median filter, IEEE Trans. Image Process 10(2), Pp.242 251, 2001. [4] G. Pok and J.-C. Liu, Decision based median filter improved by predictions, Proc. ICIP, vol. 2, pp. 410 413, 1999. [5] Punyaban Patel, Banshidhar Majhi, Bibekananda Jena, C.R.Tripathy, Dynamic Adaptive Median Filter (DAMF) for Removal of High Density Impulse Noise, International Journal of Image, Graphics and Signal Processing (IJIGSP), ISSN: 2074-9074(Print), ISSN: 2074-9082 (Online), Vol.4, No.11, pp.53-62,october 2012. [6] Zhou Wang and David Zhang, Progressive Switching Median Filter for the Removal of Impulse Noise from Highly Corrupted Images IEEE Transactions On Circuits And Systems II: Analog And Digital Signal Processing, vol. 46, no. 1, pp.78-80, January 1999. [7] Hwang, H. and Haddad, R.A., Adaptive median filters: new algorithms and results, IEEE Trans. Image Processing, vol. 4, no.4, pp.499 502, 1995. [8] Srinivasan, K.S., Ebenezer, D., A new fast and efficient decision based algorithm for removal of high-density impulse noises, IEEE Signal Processing Letters, vol. 14, no. 3, pp.189 192, 2007. Bibekananda Jena et al Page 32

[9] C. Wang, T. Chen, and Z.Qu, A Novel Improved Median Filter for Salt-and-Pepper Noise from Highly Corrupted Images, 3 rd International Symposium on Systems and Control in Aeronautics and Astronautics (ISSCAA 2010), Harbin, China, pp.718-722, IEEE, 8-10 June,2010. [10] [Shahriar Kaisar, Md. Sakib Rijwan, Jubayer Al Mahmud, and Muhammead Mizanur Rahman, Salt and Pepper Noise Detection and Removal by Tolerance based Selectve Arithmatic Mean Filtering Technique for Image Restoration, International Journal of Computer Science and Network Security, pp. 271-278, Vol.8, No.6, June 2008. [11] S.Esakkirajanet. al., Removal of high density salt and pepper noise through modified decision based unsymmetric trimmed median filter, IEEE signal processing letters, vol. 18(5), pp. 287-290, May,2011. [12] Steven W. Smith, The Scientist and Engineer s Guide to Digital Signal Processing, California Technical Publishing, San Diego, California, 1999. [13] Madhu S. Nair and G. Raju, A new fuzzy-based decision algorithm for high-density impulse noise removal, Journal of Signal, Image and Video Processing, Springer, in press, DOI 10.1007/s11760-010-0186-4, 2010. [14] Z. Wang, A. C. Bovik, H. R. Sheikh, and E. P. Simoncelli, Image quality assessment: from error visibility to structural similarity, IEEE Trans. Image Process. 13(4), 600 612 (April 2004). Author Biography Bibekananda Jena, male, is an Assistant Professor and Head in the department of Electronics and Telecommunication Engineering, Purushottam Institute of Engineering and Technology, Rourkela, India. His research interests are Image Processing, Signal Processing, Wireless and Sensor Network, Mobile Communication. He has guided many UG students. Punyaban Patel, male, is an Assistant Professor & Head, in the department of Information Technology. He is pursuing his Ph.D. under Sambalpur University. His research interests are Image Processing, Software Engineering, Wireless and Sensor Network. He has guided many UG and PG students. Banshidhar Majhi, male, is a Professor in the department of CSE, National Institute of Technology, Rourkela, India. He has published many research papers in national and international journals and conferences in the field of soft computing, image processing, biometrics, network security, wireless sensor networks etc. He has guided and produced many M.Tech and Ph.D. scholars. C.R.Tripathy, male, is a Professor in the department of CSE, VSSUT, Burla, India. He has published many research papers in national and international journals and conferences in the field of Software Engineering, Image Processing, Parallel Processing, Wireless Sensor Networks etc. He has guided and produced many M.Tech and Ph.D. scholars. B i b e k a n a n d a J e n a e t a l Page 33