ABSTRACT Preprocessing is done on the CT image of lung for removal of noise. A fuzzy filter is presented for the noise reduction of medical images corrupted with additive noise. The filter operation involves two stages. The first stage computes a fuzzy derivative for eight different directions. The second stage uses these fuzzy derivatives to perform smoothing with the fuzzification and De fuzzification operations along by weighting the contributions of neighboring pixel values. Both stages are based on fuzzy rules. The filter can be applied iteratively to effectively reduce heavy noise. In particular, the shape of the membership functions is adapted according to the remaining noise level after each iteration, making use of the distribution of the homogeneity in the image. 1. INTRODUCTION Medical imaging is the technique that is used to create images of the human body (or parts and function thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology)[3]. The CT images offer detailed information of lung cavities, which could be used for better surgical planning of treating Lung Cancer. Preprocessing is done to remove the noise from the isotropic CT image. The structure of the human lungs is shown here. Fig 1: Structure of human lungs Many existing methods are there for preprocessing. Filtering is the most fundamental operation in image processing and computer vision. The filtered image at a given location is a function of values of the input image in a small neighborhood of the same location. Assuming that images vary slowly over space, near pixels is likely to have similar values. But this assumption fails at regions that contain edges and image details (e.g. corners, lines, end of lines etc.) Most of the classical linear filters like the averaging low pass filters tend to blur and destroy the lines, edges and other fine image details Wiener filter [2] is an optimization filter aimed to minimize the mean square error between the original image and the filtered counterpart. Since noise in CT images follows the Poisson distribution, which can be approximated using a Gaussian distribution for large number of occurrences. Fuzzy image processing [4] is the collection of all approaches that understand, represent and process the images, their segments and feature as fuzzy sets. The representation and processing depend on the selected fuzzy technique and on the problem to be solved. Fuzzy image processing involves three main stages. Image fuzzification, Membership modification, Image defuzzification. Fuzzy image processing using fuzzy techniques plays a very important role in image processing. Fuzzy techniques are important and powerful tools for knowledge representation and processing, and also managing the subjectivity and uncertainty very efficiently. The three important areas that are not perfect are Greyness ambiguity, Geometrical fuzziness, vague knowledge. Fuzzy Geometry, measures of Fuzziness and image information, fuzzy inference systems, fuzzy clustering, Fuzzy mathematical morphology, fuzzy measure theory, Fuzzy Grammars, neural fuzzy are some of important theoretical components of fuzzy image processing scheme. Median filtering is similar to using an averaging filter, in that each output pixel is set to an average of the pixel values in the neighborhood of the corresponding input pixel. However, with median filtering, the value of an output pixel is determined by the median of the neighborhood pixels, rather than the mean. Median filtering is a specific case of order-statistic filtering
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