共查询到20条相似文献,搜索用时 15 毫秒
1.
Quadratic Volterra filters are effective in image sharpening applications. The linear combination of polynomial terms, however, yields poor performance in noisy environments. Weighted median (WM) filters, in contrast, are well known for their outlier suppression and detail preservation properties. The WM sample selection methodology is naturally extended to the quadratic sample case, yielding a filter structure referred to as quadratic weighted median (QWM) that exploits the higher order statistics of the observed samples while simultaneously being robust to outliers arising in the higher order statistics of environment noise. Through statistical analysis of higher order samples, it is shown that, although the parent Gaussian distribution is light tailed, the higher order terms exhibit heavy-tailed distributions. The optimal combination of terms contributing to a quadratic system, i.e., cross and square, is approached from a maximum likelihood perspective which yields the WM processing of these terms. The proposed QWM filter structure is analyzed through determination of the output variance and breakdown probability. The studies show that the QWM exhibits lower variance and breakdown probability indicating the robustness of the proposed structure. The performance of the QWM filter is tested on constant regions, edges and real images, and compared to its weighted-sum dual, the quadratic Volterra filter. The simulation results show that the proposed method simultaneously suppresses the noise and enhances image details. Compared with the quadratic Volterra sharpener, the QWM filter exhibits superior qualitative and quantitative performance in noisy image sharpening. 相似文献
2.
Vector median filters 总被引:21,自引:0,他引:21
Astola J. Haavisto P. Neuvo Y. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1990,78(4):678-689
Two nonlinear algorithms for processing vector-valued signals are introduced. The algorithms, called vector median operations, are derived from two multidimensional probability density functions using the maximum-likelihood-estimate approach. The underlying probability densities are exponential, and the resulting operations have properties very similar to those of the median filter. In the vector median approach, the samples of the vector-valued input signal are processed as vectors. The operation inherently utilizes the correlation between the signal components, giving the filters some desirable properties. General properties as well as the root signals of the vector median filters are studied. The vector median operation is combined with linear filtering, resulting in filters with improved noise attenuation and filters with very good edge response. An efficient algorithm for implementing long vector median filters is presented. The noise attenuation of the filters is discussed, and an application to velocity filtering is shown 相似文献
3.
《Signal processing》1987,13(3):287-299
Median filters (MF) are used both to filter ‘salt and pepper’ noise from signals and images and in other signal processing applications. In this paper, an extension of the MF, the vector median filter (VMF), is introduced. As opposed to the MF, the VMF outputs for each window location a number of data elements. By adjusting the VMF parameters, the MF is obtained as a VMF special case. Just like the MF, the VMF filters impulses while simultaneously preserving step changes in a signal. The VMF's principal advantage is that it reduces the total stored data signal computation time while it produces visual outputs comparable to that of an MF. Deterministic and statistical properties of the VMF are examined. Computer-generated experimental results are also presented. 相似文献
4.
Topological median filters 总被引:11,自引:0,他引:11
This paper describes the definition and testing of a new type of median filter for images. The topological median filter implements some existing ideas and some new ideas on fuzzy connectedness to improve, over a conventional median filter, the extraction of edges in noise. The concept of alpha-connectivity is defined and used to create an algorithm for computing the degree of connectedness of a pixel to all the other pixels in an arbitrary neighborhood. The resulting connectivity map of the neighborhood effectively disconnects peaks in the neighborhood that are separated from the center pixel by a valley in the brightness topology. The median of the connectivity map is an estimate of the median of the peak or plateau to which the center pixel belongs. Unlike the conventional median filter, the topological median is relatively unaffected by disconnected features in the neighborhood of the center pixel. Four topological median filters are defined. Qualitative and statistical analyses of the four filters are presented. It is demonstrated that edge detection can be more accurate on topologically median filtered images than on conventionally median filtered images. 相似文献
5.
Partition-based Weighted Sum (P-WS) filtering is an effective method for processing nonstationary signals, especially those with regularly occurring structures, such as images. P-WS filters were originally formulated as Hard-partition Weighted Sum (HP-WS) filters and were successfully applied to image denoising. This formulation relied on intuitive arguments to generate the filter class. Here we present a statistical analysis that justifies the use of weighted sum filters after observation space partitioning. Unfortunately, the HP-WS filters are nondifferentiable and an analytical solution for their global optimization is therefore difficult to obtain. A two-stage suboptimal training procedure has been reported in the literature, but prior to this research no evaluation on the optimality of this approach has been reported. Here, a Genetic Algorithm (GA) HP-WS optimization procedure is developed that, in simulations, shows that the simpler two-stage training procedure yields near optimal results. Also developed in this paper are Soft-partition Weighted Sum (SP-WS) filters. The SP-WS filters utilize soft, or fuzzy, partitions that yield a differentiable filtering operation, enabling the development of gradient-based optimization procedures. Image denoising simulation results are presented comparing HP-WS and SP-WS filters, their optimization procedures, and wavelet-based image denoising. These results show that P-WS filters, in general, outperform traditional and wavelet-based image filters, and SP-WS filters utilizing soft partitioning not only allow for simple optimization, but also yields improved performance. 相似文献
6.
Convergence properties of median and weighted median filters 总被引:1,自引:0,他引:1
Bing Zeng 《Signal Processing, IEEE Transactions on》1994,42(12):3515-3518
It has been shown that assuming the first and last value carry-on appending strategy, a finite number of passes of the same median filter to an arbitrary signal of finite length results in a root signal that will be invariant to additional filtering passes. This so-called convergence property is reproven using an extremely simple approach. In addition, the well-known idempotent property (i.e., where convergence is achieved with only one filtering pass) of a recursive median filter is reproven similarly, and the convergence behavior of weighted median filters is studied 相似文献
7.
《Signal processing》2007,87(9):2085-2099
A sharpening vector median (VM) filter for simultaneous denoising and enhancing vector-valued signals is introduced. This filter uses the trimmed aggregated distance minimization concept and robust vector order statistics to enhance edges and image details while retaining the noise removal characteristics of the standard VM operator. The procedure accommodates various design, implementation and application objectives by enhancing the vector-valued signals depending on the local image statistics and/or the user's needs. The filter properties discussed in this paper are proven and suggest that the proposed solution is a robust vector processing operator. The performance and efficiency of the filter are analyzed and commented upon. Examples from its application to color image filtering and virtual restoration of artworks are provided. 相似文献
8.
A binary annular filter removes isolated points in the foreground and the background of an image. Here, the adjective "isolated" refers to an underlying adjacency relation between pixels, which may be different for foreground and background pixels. In this paper, annular filters are represented in terms of switch pairs. A switch pair consists of two operators which govern the removal of points from foreground and background, respectively. In the case of annular filters, switch pairs are completely determined by foreground and background adjacency. It is shown that a specific triangular condition in terms of both adjacencies is required to establish idempotence of the resulting annular filter. In the case of translation-invariant operators, an annular filter takes the form X-->(X plus sign in circleA) intersectionX union or logical sum(X minus sign in circleB), where A and B are structuring elements satisfying some further conditions: when A intersectionB intersection(A plus sign in circleB) not equal?, it is an (idempotent) morphological filter; when A union or logical sumB subsetA plus sign in circleB, it is a strong filter and in this case it can be obtained by composing in either order the annular opening X-->(X plus sign in circleA) intersectionX and the annular closing X--> union or logical sum(X plus sign in circleB). 相似文献
9.
Generalized multistage median filters. 总被引:1,自引:0,他引:1
X Wang 《IEEE transactions on image processing》1992,1(4):543-545
As an extension of the multistage median filters, a class of r -filters is presented. Some properties of these filters are discussed. It is shown that the filters can smooth noise and preserve details of images efficiently. 相似文献
10.
Bottema M.J. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(6):1629-1640
Two key deterministic properties of analog median filters are established. The first is that root signals are characterized by a special class of locally monotone functions, and the second is that the repeated application of a median filter produces a root signal which retains significant features in the original data. Both results are extensions of well known facts for discrete median filters. In addition, it is shown that these properties do not extend to a natural multidimensional version of the median filter 相似文献
11.
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1987,75(11):1542-1544
Median filtering is a simple digital technique for smoothing signals. A root signal is defined as an invariant signal to the median filtering. We describe directed graph representation for the root-signal set of median filters. The directed graph representation allows us to obtain a set of roots and the number of roots in a straightforward manner. 相似文献
12.
We consider the use of nonlinear estimators for the noise smoothing of images obtained under quantum-limited imaging conditions. A Volterra expansion is investigated from which a set of linear-quadratic filters is derived using higher order statistics. The filters are applicable for single frame and multiple frames of a single scene imaged under low-light levels. 相似文献
13.
Karl W.C. Leeb S.B. Jones L.A. Kirtley J.L. Verghese G.C. 《Power Electronics, IEEE Transactions on》1992,7(3):437-443
A class of robust, rank-based signal processing filters is considered, particularly with regard to its usefulness in the power electronics field. This class of nonlinear filters is characterized by the inclusion of a sorting element in the signal path. The sorting operation allows these filters to suppress impulsive noise while preserving edges and monotonic sections of signals. This introductory work concentrates primarily on the median filter, it being the most accessible filter of the class. A working knowledge of issues arising in design and implementation is developed 相似文献
14.
15.
Analysis of two-dimensional center weighted median filters 总被引:2,自引:0,他引:2
Tong Sun Moncef Gabbouj Yrjö Neuvo 《Multidimensional Systems and Signal Processing》1995,6(2):159-172
Center weighted median (CWM) filters, which have been recognized as detail preserving filters, are an important and the simplest subclass of weighted median (WM) filters. In this paper, we analyze the root signals of two-dimensional (2-D) CWM filters. In particular, we derive the required form for a signal to be a root of a 2-D CWM filter. The required form of signals to be roots is then used to evaluate the detail preserving properties of 2-D CWM filters. As examples, the detail preserving properties of some 2-D CWM filters are compared with other detail preserving filters, i.e. multilevel median filters. The generation of binary root signals of some 2-D CWM filters is treated in the term of the smallest surviving object (SSO). It is illustrated by some examples that CWM filters with different orientation of windows can be useful in image segmentation. 相似文献
16.
Digital decimation filters play a fundamental role in oversampled sigma-delta A/D decoders. In this paper, we first show that weighted median (WM) filtering of a demodulated sequence (at the Nyquist rate) can be implemented concurrently in the A/D decoder. Through a simple modification of the binary time-series outputted by the A/D modulator, the sequence obtained after the sigma-delta modulation (SDM) decoder is shown to be equivalent to WM filtering the multilevel sequence at the Nyquist rate. Second, we show that WM filters can be used for SDM decimation filters and that these filters are readily implemented in the SDM binary domain. A very promising characteristic of SDM converters equipped with WM decimating filters is that sharp discontinuities (edges) can be preserved and acquired. Thus, the bandlimited constraint imposed on the input signals can be relaxed making SDM more attractive to A/D conversion of signals containing sharp transitions. The proposed signal processing algorithms, in essence, combine A/D sigma-delta converters and WM filters into a single programmable system 相似文献
17.
Fast adaptive optimization of weighted vector median filters 总被引:1,自引:0,他引:1
Weighted vector median (WVM) filters are effective tools for multichannel signal processing. To obtain the desired filtering behavior and characteristic, the WVM filter weights must be determined in an appropriate manner. In this paper, we first analyze previously defined approaches for WVM filter optimization and show their drawbacks related to derivative computation and vector direction information utilization. Based on this analysis, we propose two fast adaptive algorithms for WVM filter design. Proposed Algorithm I computes locally optimal weight changes at each iteration and updates the filter weights accordingly. This algorithm does not involve derivative computation, thus eliminating the instability caused by derivative approximations utilized in previous approaches. Proposed Algorithm II extends the results from established marginal weighted median optimization methods to the vector case by error metric generalization. Both algorithms can be applied to WVM filters using the L/sub p/ norm, while Algorithm I can operate on more general distance metrics. The presented simulation results show that both algorithms are effective, fast, and stable; they perform well under a wide range of circumstances. 相似文献
18.
Vassiliou A.A. Boulianne M. Blais J.A.R. 《Geoscience and Remote Sensing, IEEE Transactions on》1988,26(6):832-838
The application of averaging median filters to remote sensing has been investigated, and the results are presented with some discussion and recommendations. Averaging median filters can be considered as a subclass of the standard median filters. For image processing purposes, a two-dimensional window is first filtered by a number of average filters, and the final result of the averaging filters is equal to the median of the central pixel value and the averaging filter results. Applications of this averaging median filter to Landsat images are presented, and the results show that the fine details are preserved while attenuating the impulsing noise 相似文献
19.
Adaptive median filters: new algorithms and results 总被引:39,自引:0,他引:39
Based on two types of image models corrupted by impulse noise, we propose two new algorithms for adaptive median filters. They have variable window size for removal of impulses while preserving sharpness. The first one, called the ranked-order based adaptive median filter (RAMF), is based on a test for the presence of impulses in the center pixel itself followed by a test for the presence of residual impulses in the median filter output. The second one, called the impulse size based adaptive median filter (SAMF), is based on the detection of the size of the impulse noise. It is shown that the RAMF is superior to the nonlinear mean L(p) filter in removing positive and negative impulses while simultaneously preserving sharpness; the SAMF is superior to Lin's (1988) adaptive scheme because it is simpler with better performance in removing the high density impulsive noise as well as nonimpulsive noise and in preserving the fine details. Simulations on standard images confirm that these algorithms are superior to standard median filters. 相似文献
20.
Wanzhsu Ye Xingwei Zhou 《Signal Processing, IEEE Transactions on》2001,49(2):360-363
Repeated application of the median filter to any finite length sequence converges to a root in a finite number of passes. This requires padding on each end of the sequence. In some applications, such padding may be inappropriate because of the overemphasis on the endpoints. However, there are some of infinite-length sequences whose median filters are not convergent. In this paper, necessary and/or sufficient conditions on infinite-length sequences are derived in order that their median filters converge to roots of category I. Moreover, we study convergence of median filters of perturbed sequences. The results obtained extend the previous theory on convergence of median filters 相似文献