Restoration of images contaminated by mixed Gaussian and impulsenoise using a recursive minimum-maximum method

A technique is proposed for removing impulse noise in images, called the recursive minimum-maximum method. Statistical analysis of this method indicates that it is good at preserving fine details and suppressing impulse noise at the same time. Experimental results show that the technique is robust and produces better restored images under various impulse noise conditions than other median filter-based methods     

Blind quality assessment of tone-mapped images using multi-exposure sequences

The tone mapping operator (TMO) enables high dynamic range (HDR) images to be presented on low dynamic range (LDR) consumer electronic devices. However, the results obtained by this method are not always ideal due to the reduced number of bits. In comparison, the multi-exposure image fusion (MEF) bypasses the intermediate HDR image composition and directly produces an image presented on standard devices. Inspired by this, this paper proposes a quality assessment method for tone-mapped image (TMI) based on generating multi-exposure sequences. Specifically, the method uses a generative adversarial network (GAN) to generate a set of sequences with different exposure levels based on the TMIs. Then a two-branch convolutional neural network (CNN) is used to extract features from the tone-mapped images and the multi-exposure reference sequences, respectively. Finally, the transformer is used to mine the intrinsic connections between TMIs and multi-exposure sequences and learn the mapping relationships from feature space to quality space. We conducted extensive experiments on the ESPL-LIVE HDR database. The applicability and effectiveness of the proposed method are verified by comparing and analyzing relevant features and model configurations with existing mainstream evaluation algorithms.     

Fusion of hyperspectral and panchromatic images with guided filter

Guided filter has been widely used in image fusion. However, most of the guided filter-based fusion methods generate the spatial detail image by making a compromise between the spatial detail of the panchromatic (PAN) and that of the hyperspectral (HS) intensity component. The intensity component cannot well present the edge and texture features of the HS image. The spectral distortion usually occurs due to the injected redundant spatial detail. To overcome this problem, this study presents a novel HS image fusion method by taking the advantage of the guided filter. The characteristics of the PAN and HS images are simultaneously considered. The guided filter is employed to generate the spatial detail image of each HS image band successively. The generated spatial detail image is further optimized by minimizing the difference between each band of the spatial detail image and its corresponding band of the HS image, with the help of a novel injection gains matrix. Experiments performed on various satellite datasets demonstrate that the superiority of the proposed method in spectral maintenance and spatial quality aspects.     

Detection and measurement of retinal vessels in fundus images using amplitude modified second-order Gaussian filter

In this paper, the fitness of estimating vessel profiles with Gaussian function is evaluated and an amplitude-modified second-order Gaussian filter is proposed for the detection and measurement of vessels. Mathematical analysis is given and supported by a simulation and experiments to demonstrate that the vessel width can be measured in linear relationship with the "spreading factor" of the matched filter when the magnitude coefficient of the filter is suitably assigned. The absolute value of vessel diameter can be determined simply by using a precalibrated line, which is typically required since images are always system dependent. The experiment shows that the inclusion of the width measurement in the detection process can improve the performance of matched filter and result in a significant increase in success rate of detection.     

An adaptive recursive 2-D filter for removal of Gaussian noise inimages

A 2D recursive low-pass filter with adaptive coefficients for restoring images degraded by Gaussian noise is proposed. Some of the ideas developed are also submitted for nonGaussian noise. The adaptation is performed with respect to three local image features-edges, spots, and flat regions-for which detectors are developed by extending some existing methods. It is demonstrated that the filter can easily be extended so that simultaneous noise removal and edge enhancement is possible. A comparison with other approaches is made. Some examples illustrate the performance of the filter.     

Moving-target-indicator recursive radar filter using bucket-brigade circuits

A prototype clutter-rejection filter for radar is described. It uses analogue shift registers of the bucket-brigade type, which, in common with charge-coupled devices, can combine the flexibility of digital processing with the simplicity of analogue operation. Certain imperfections in the devices are shown to be particularly important for moving-target-indicator filtering.     

FSK demodulation using an adaptive recursive digital filter

A second-order adaptive recursive digital filter is used for frequency-shift keying (FSK) demodulation. Explicit formulas are derived for the noise variance in the frequency detector, and optimum transmitter carrier frequencies and detector threshold frequencies are calculated. A formula for the adaptation time is derived and the error probability is found. Computer simulations verify the derived results     

Wavelets and recursive filter banks

It is shown that infinite impulse response (IIR) filters lead to more general wavelets of infinite support than finite impulse response (FIR) filters. A complete constructive method that yields all orthogonal two channel filter banks, where the filters have rational transfer functions, is given, and it is shown how these can be used to generate orthonormal wavelet bases. A family of orthonormal wavelets that have a maximum number of disappearing moments is shown to be generated by the halfband Butterworth filters. When there is an odd number of zeros at π it is shown that closed forms for the filters are available without need for factorization. A still larger class of orthonormal wavelet bases having the same moment properties and containing the Daubechies and Butterworth filters as the limiting cases is presented. It is shown that it is possible to have both linear phase and orthogonality in the infinite impulse response case, and a constructive method is given. It is also shown how compactly supported bases may be orthogonalized, and bases for the spline function spaces are constructed     

基于自适应Volterra的高斯噪声图像滤波算法

针对高斯噪声图像滤波问题,提出一种可以保留细节的自适应Volterra-Volterra滤波方法。为了解决二阶Volterra滤波器核系数确定难、数量多等问题,提出了一种自适应建核结构及算法。通过图像处理实验,与其它滤波算法进行了细节度保留、均方差(MSE)和信噪比(SNR)等指标的比较,结果表明,本文方法优于进行对比的其它滤波方法。     

An improved recursive LMS algorithm using a modified gradient filter

The purpose of this letter is to discuss the application of a modified gradient filtering technique proposed by Friedlander [1] to the modified recursive least mean square (RLMS) algorithm of Hsia [2].     

A high-speed low-cost recursive digital filter using residue number arithmetic

Use of table look-up multiplication by fractional coefficients allows implementation of high-speed, low-cost recursive digital filters using residue number arithmetic. An 8-bit equivalent filter based on the lossless discrete integrator (LDI) technique described by Bruton can be easily implemented using inexpensive commercially available PROM's for the table look-up. Computer Simulations of first- and second-order LDI-RNS filters indicate substantial cost savings and speed advantages. Experiments on a first-order section verify the basic operation, speed calculations, and cost analysis. Furthermore, extensions to more bits and higher order filters are possible.     

Subband coding of images using asymmetrical filter banks

We address the problem of the choice of subband filters in the context of image coding. The ringing effects that occur in subband-based compression schemes are the major unpleasant distortions. A new set of two-band filter banks suitable for image coding applications is presented. The basic properties of these filters are linear phase, perfect reconstruction, asymmetric length, and maximum regularity. The better overall performances compared to the classical QMF subband filters are explained. The asymmetry of the filter lengths results in a better compaction of the energy, especially in the highpass subbands. Moreover, the quantization error is reduced due to the short lowpass synthesis filter. The undesirable ringing effect is considerably reduced due to the good step response of the synthesis lowpass filter. The proposed design takes into account the statistics of natural images and the effect of quantization errors in the reconstructed images, which explains the better coding performance.     

An adaptive recursive LMS filter

An adaptive, recursive, least mean-square-digital filter is heuristically derived that has the computational simplicity of existing transversal adaptive filters, with the additional capability of producing poles in the filter transfer function. Simulation results are presented to demonstrate its capability.     

High-speed recursive digital filter realization

Pipeline techniques have been successfully applied to speeding up processing in both general- and special-purpose digital computers. Application of these techniques to nonrecursive (FIR) filters has been suggested and is quite straightforward. Application to recursive (IIR) filters has not previously been shown. In this paper, the technique for applying pipeline techniques to recursive filters is shown and the advantages and disadvantages of the technique are discussed. Using these techniques, recursive digital filters operating at hitherto impossibly high rates can be designed.The basic research for this idea was supported by the Department of Electrical and Computer Engineering, University of California, Davis, California 95616. The basic idea is the subject of a pending patent application. Subsequent research was supported by the U.S. Naval Electronic Systems Command.On leave from the Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA.     

New charge transfer recursive filter

A new fully integrated recursive charge transfer filter is described using the concept of passive recirculation of charges. This is a novel solution for voice channel or data filters in digital communications.     

Extended Gaussian images

This is a primer on extended Gaussian images. Extended Gaussian images are useful for representing the shapes of surfaces. They can be computed easily from: 1. needle maps obtained using photometric stereo; or 2. depth maps generated by ranging devices or binocular stereo. Importantly, they can also be determined simply from geometric models of the objects. Extended Gaussian images can be of use in at least two of the tasks facing a machine vision system: 1. recognition, and 2. determining the attitude in space of an object. Here, the extended Gaussian image is defined and some of its properties discussed. An elaboration for nonconvex objects is presented and several examples are shown.     

Gradient field multi-exposure images fusion for high dynamic range image visualization

This paper presents a novel method for fusing multi-exposure images into a low dynamic range (LDR) image that is suitable for display and visualization but it contains details in the high dynamic range (HDR) counterpart. Fused gradient field is derived from the structure tensor of inputs based on multi-dimensional Riemannian geometry with a Euclidean metric assumed. Afterwards, a new method is proposed for modifying the gradient field iteratively with twice average filtering and nonlinearly compressing in multi-scales. These modification operations are all done at the finest resolution. The result is obtained through solving a Poisson equation then linearly stretching to the common range. Experimental results demonstrate the efficiency and effectiveness of this method.     

A simplified adaptive recursive filter design

The adaptive recursive filter design first proposed by White [1] is re-examined, and a modified filter configuration is proposed which drastically simplifies the gradient generating mechanism. The performance behavior of the simplified filter design is analyzed.     

（英）基于多尺度高斯滤波和形态学变换的红外与其他类型图像融合方法

为了同时保证融合质量和效率,提出了一种基于多尺度高斯滤波和形态学变换的图像融合方法。设计了多尺度高斯滤波,将源图像分解为一系列细节图像和近似图像,并使用多尺度顶帽和底帽分解来完全提取近似图像中不同尺度的明暗细节。构造了多尺度形态学内外边缘分解,以充分提取细节图像的边缘信息。实验结果表明,该方法与典型的基于多尺度分解的融合方法相当甚至更好,同时比一些先进的基于多尺度分解的方法（如NSCT和NSST）运算速度快得多。     

A recursive digital MTI radar filter

An approach for designing a recursive digital MTI radar filter in the z plane is described. The resultant filter exhibits a sharp spectrum rolloff and an almost flat passband in the amplitude response.