Realization of rank order filters based on majority gate

Abstract

Abstract--A new technique for the implementation of a single hardware structure capable of computing any rank order filter is presented in this paper. The proposed technique, which is based on the majority gate, achieves faster extraction of setting flag signals and, therefore, shorter processing times are attained. A pipelined systolic array, suitable for performing rank order filtering, is also presented. Applications of rank order filters include digital image processing, speech processing and coding and digital TV applications. ~ 1997 Pattern Recognition Society. Published by Elsevier Science Ltd. Nonlinear filtersComputer visionRank order filters are a class of nonlinear filters. The input of such filters is a window of data with an odd number of elements. These elements are sorted in ascending order and the output of the rank order filter with rank r is the rth element (rth order statistic)J 1) Special cases of rank order filters are median, minimum and maximum filters, where the outputs are the median, the minimum and the maximum values of the input data window, respectively. Rank order filters exhibit excellent robustness properties and provide solutions in many cases where linear filters are inappropriate. They can suppress high-frequency and impulse noise in an image, avoiding at the same time extensive blurting of the image, since they have good edge preservation properties. They have found numerous applications, such as in digital image analysis, in speech processing and coding, in digital TV applications, etc. (~'2) Median and rank order filters are strongly related with morphological filters, another class of nonlinear illters. (3'4) It has been shown that erosions and dilations are special cases of rank order filters and that any rank order filter can be expressed either as a maximum of erosions or as a minimum of dilations. °) Therefore, algorithms which originally have been devised for rank order and median filters can be used for realization of morphological operators. (5'6) Several algorithms have been proposed for the realization of rank order filters, such as tree sorts, shell sorts and quick sorts. (1) Although these algorithms are suitable for software implementation, they result in inefficient hardware structures, since they handle the numbers in wordlevel. Rank order filters can be implemented in VLSI

Deep imaging of the shell elliptical galaxy NGC 3923 with MegaCam

“…The dilatation operation is defined like the erosion, only the minimum is substituted by the maximum. Moreover, these methods implement a noise-smoothing step (e.g., Gasteratos et al 1998or Yu-qian et al 2006. Here the similarity with minimum masking ends.…”

Binary, gray-scale, and vector soft mathematical morphology: Extensions, algorithms, and implementations

“…The majority selection procedure continues in the next stages until the median value is found. Gasteratos et al (1997a) have proposed an improvement of this algorithm for the implementation of any rank filter using a single hardware structure. This is based on the concept that by having a method to compute the median value of 4N + 1 numbers and by being able to control 2N of these numbers,…”

A parallel architecture for implementation of filters based on order statistics

“…sation based on the majority gate MG has been Ž . presented by Gasteratos et al 1997 . A comparative study for median filter implementation using 3 = 3 pixel image data of 8-bit resolution is shown in Table 1.…”

“…This is due to the fact that the processing element of the MG technique consists of only three Ž . levels of gates Gasteratos et al, 1997 , whilst each compare and swap element consists of eight levels of Ž . gates includes a comparator and a multiplexer .…”