Inverse Filtering Research Articles

Digital reconstruction of infraslow activity in human intracranial ictal recordings using a deconvolution-based inverse filter

Infraslow activity (ISA) is a biomarker that has recently become of interest in the characterization of seizure recordings. Recent data from a small number of studies have suggested that the epileptogenic zone may be identified by the presence of ISA. Investigation of low frequency activity in clinical seizure recordings, however, has been hampered by technical limitations. EEG systems necessarily include a high-pass filter early in the measurement chain to remove large artifactual drifts that can saturate recording elements such as the amplifier. This filter, unfortunately, attenuates legitimately seizure-related low frequencies, making ISA difficult to study in clinical EEG recordings. In this study, we present a deconvolution-based digital inverse filter that allows recovery of attenuated low frequency activity in intracranial recordings of temporal lobe epilepsy patients. First, we show that the unit impulse response (UIR) of an EEG system can be characterized by differentiation of the system’s step response. As proof of method, we present several examples that show that the low frequency component of a high-pass filtered signal can be restored by deconvolution with the UIR. We then demonstrate that this method can be applied to biologically relevant signals including clinical EEG recordings obtained from seizure patients. Finally, we discuss how this method can be applied to study ISA to identify and assess the seizure onset zone.

A tailored indoor setup for reproducible passive daytime cooling characterization

SummaryPassive daytime cooling materials can lower global energy consumption owing to their autonomous cooling capability. Although a significant number of passive cooling materials have been developed recently, their performance characterization is still challenging. Field tests experience high variability due to uncontrollable changes in environmental conditions. Here, we design an indoor setup to characterize the performance of passive cooling materials reproducibly and independently of weather and season. Outdoor measurement conditions are approximated using a liquid-nitrogen-cooled aluminum dome, a solar simulator, and a wavelength-selective inverse sky-window filter. In contrast to outdoor measurements, the results of various reference materials show remarkable precision and repeatability. Additionally, the impact of solar light intensity and temperature on the passive cooling performance can be experimentally investigated. Our setup is a first step in the development of a standardized test method to bring accuracy, reproducibility, and comparability to the emerging field of passive cooling materials.

CoLiTecVS software for the automated reduction of photometric observations in CCD-frames

In this article, we present the new product and its description developed by the CoLiTec (Collection Light Technology) project (Khlamov & Savanevych 2020), called CoLiTecVS (CoLiTec Variable Stars) software as a set of tools for the automated light curve creation of variable stars using the sensor data received from the different sensors.CoLiTecVS allows performing the photometry and light curve creation with minimal user interaction in two different modes. The first one is an observation mode when the data are received online from the sensors directly and immediately processed by the OnLine Data Analysis System (OLDAS). This mode is called “OLDAS-Night” mode. The second one is processing the existing observations when sensor data are already received and saved. This mode is called ”CoLiTec-Day” mode.Nowadays, the modern sensors (robotic ground-based telescopes equipped with different cameras with charge-coupled device (CCD)) still have a lack of capabilities, like non-uniform sensitivity of the matrix pixels, non-linearity of the pixel response to the number of photons that have fallen, oversaturation of bright objects leads to charge transfer to neighboring pixels and the presence of cold or hot pixels. All these shortcomings of modern sensors complicate the process of obtaining the accurate photometric measurements. Such lack of capabilities of modern sensors also makes the plotting of light curves a difficult and routine task. The latter shifts astronomer’s main attention from research to the very time-consuming tasks of processing sensor data and light curve creation. To solve this problem, we developed a new tool for the automated reduction of photometric observations, which includes the computational method for the brightness assessment of the investigated and comparison stars; brightness equalization of astronomical images using an inverse median filter; and light curve plotting and its processing using different tools.This new CoLiTecVS software provides a tool for high accurate stellar brightness measuring and automated light curve creation with aperture photometry uncertainties less than 0.04 magnitude, the value of which generally depends on various imaging characteristics of telescopes, detectors, and sensors.CoLiTecVS has been tested on many different time series of 20-600 CCD-frames with variable stars and has produced high-quality photometric light curves in a fraction of the usual processing time.

Comparison of inversion methods in MR elastography: An open-access pipeline for processing multifrequency shear-wave data and demonstration in a phantom, human kidneys, and brain.

Magnetic resonance elastography (MRE) maps the viscoelastic properties of soft tissues for diagnostic purposes. However, different MRE inversion methods yield different results, which hinder comparison of values, standardization, and establishment of quantitative MRE markers. Here, we introduce an expandable, open-access, webserver-based platform that offers multiple inversion techniques for multifrequency, 3D MRE data. The platform comprises a data repository and standard MRE inversion methods including local frequency estimation (LFE), direct-inversion based multifrequency dual elasto-visco (MDEV) inversion, and wavenumber-based (k-) MDEV. The use of the platform is demonstrated in phantom data and in vivo multifrequency MRE data of the kidneys and brains of healthy volunteers. Detailed maps of stiffness were generated by all inversion methods showing similar detail of anatomy. Specifically, the inner renal cortex had higher shear wave speed (SWS) than renal medulla and outer cortex without lateral differences. k-MDEV yielded higher SWS values than MDEV or LFE (full kidney/brain k-MDEV: 2.71 ± 0.19/1.45 ± 0.14 m/s, MDEV: 2.14 ± 0.16/0.99 ± 0.11 m/s, LFE: 2.12 ± 0.15/0.89 ± 0.06 m/s). The freely accessible platform supports the comparison of MRE results obtained with different inversion methods, filter thresholds, or excitation frequencies, promoting reproducibility in MRE across community-developed methods.

First‐order inverse filters: Implementations using a single voltage conveyor and potential applications

SummaryFirst‐order low pass and high pass inverse filter topologies, offering simplicity and independent adjustment of the gain and the characteristic frequency, are introduced in this work. These features are offered thanks to the terminals properties of the second generation voltage conveyor. In addition, possible applications of these types of filters are exploited. The behavior of a control system, where these filters are incorporated, is evaluated in both frequency and time‐domain using the Cadence IC design suite.

Detailing the target interval of the section by increasing the resolution of the data using the optimal parameters of reverse filtration in the Kurovdag and Hovsany areas of Azerbaijan

The article discusses ways to improve the resolution of seismic surveys. It is noted that this issue has been in the focus of attention of geophysicists since the early stages of the application of this method and has not lost its relevance at present. The criteria for the resolution of seismic surveys are recalled, among which the Rayleigh criterion has received wide application. It is noted that the geological environment behaves like a filter, absorbing the high-frequency components of the waves increases the wavelength, thereby deteriorating the resolution. It is brought to the attention that in the mid-fifties Robinson proposed reverse filtering, which is still widely used in the practice of seismic exploration. Here, the main emphasis is on the fact that the choice of deconvolution parameters (inverse filter) is very important, which is demonstrated on the seismic trace model. The main part of the article presents the results of applying the optimal deconvolution parameters in two fairly old fields in Azerbaijan - Kurovdag and Govsany, which have different surface and deep seismogeological conditions located in different oil and gas regions. The main geological and geophysical information about these fields is given, then the results of applying the optimal operators of predictive deconvolution are described in sufficient detail. It is noted that due to the fact that these deposits have been in operation for quite a long time and therefore their prospects are of course connected by smaller objects, and elucidation of finer features of the section in such deposits is of paramount importance and it was possible to elucidate the fine structure of the lower productive strata (Kyurovdag) and the Kalinskaya suite (Govsany) of the productive strata, belonging to the lower Pliocene. It is these deposits that attract the attention of geologists and geophysicists at the present time.

Fast least-squares prestack time migration via accelerating the explicit calculation of Hessian matrix with dip-angle Fresnel zone

Amplitude versus offset analysis is a fundamental tool for determining the physical properties of reservoirs but generally hampered by the blurred common image gathers (CIGs). The blurring can be optimally corrected using the blockwise least-squares prestack time migration (BLS-PSTM), where common-offset migrated sections are divided into a series of blocks related to the explicit offset-dependent Hessian matrix and the following inverse filtering is iteratively applied to invert the corresponding reflectivity. However, calculating the Hessian matrix is slow. We present a fast BLS-PSTM via accelerating Hessian calculation with dip-angle Fresnel zone (DFZ). DFZ is closely related to optimal migration aperture, which significantly attenuates migration swings and reduces the computational cost of PSTM. Specifically, our fast BLS-PSTM is implemented as a two-stage process. First, we limit the aperture for any imaging point with an approximated the projected Fresnel zone before calculating the Hessian matrix. Then, we determine whether a seismic trace contributes to the imaging point via DFZ during calculating the Hessian matrix. Numerical tests on synthetic and field data validate the distinct speedup with higher-quality CIGs compared to BLS-PSTM.

Antisloshing Trajectories for High-Acceleration Motions in Automatic Machines

Abstract This paper studies the design of antisloshing trajectories for application in automatic machines for packaging liquid products, with specific reference to cylindrical containers and emphasis on prescribed motion durations. Different strategies, based on a discrete linear model of the sloshing phenomenon and applicable in real-time, are analyzed to perform antisloshing feedforward control of the container motion: finite impulse response (FIR) filters (input shapers and others), dynamic-model inversion, and infinite impulse response (IIR) filters. Unlike the previous literature, these strategies are applied to highly dynamical motion laws, with maximum accelerations from 4 m/s2 to 13 m/s2. The effectiveness of the proposed antisloshing trajectories is assessed by experiments.

Further Generalization and Approximation of Fractional-Order Filters and Their Inverse Functions of the Second-Order Limiting Form

This paper proposes a further generalization of the fractional-order filters whose limiting form is that of the second-order filter. This new filter class can also be regarded as a superset of the recently reported power-law filters. An optimal approach incorporating constraints that restricts the real part of the roots of the numerator and denominator polynomials of the proposed rational approximant to negative values is formulated. Consequently, stable inverse filter characteristics can also be achieved using the suggested method. Accuracy of the proposed low-pass, high-pass, band-pass, and band-stop filters for various combinations of design parameters is evaluated using the absolute relative magnitude/phase error metrics. Current feedback operational amplifier-based circuit simulations validate the efficacy of the four types of designed filters and their inverse functions. Experimental results for the frequency and time-domain performances of the proposed fractional-order band-pass filter and its inverse counterpart are also presented.

Comparison of waveform estimated using inverse filtering with direct measurement of the volume flow at the glottal exit

Inverse filtering is a signal processing technique used to estimate the glottal waveform from the speech signal. Although this technique is regularly used in research studies, it has never been formally validated because of the difficulties in obtaining direct measurements of the glottal airflow. The objective of this study is a first step towards validating this technique by comparing its estimated glottal waveform with flow measurements taken simultaneously at the glottal exit. The setup is based on synthetic vocal folds connected to a vocal tract model. Direct measurements of the volume flow at the glottal exit are taken using time-resolved tomographic particle image velocimetry. A circumferentially vented pneumotachograph (i.e., Rothenberg) mask is connected to the vocal tract and used with the Glottal Enterprise system to calculate the glottal waveform using inverse filtering. Effect of varying subglottal pressures and effect of near-field (i.e., the minimal gap between the false vocal folds) and far-field (i.e., oral opening) constrictions were also investigated. Results show that overall using inverse filtering gives a good approximation of the glottal flow waveform, but its accuracy can change depending on the constrictions in the vocal tract. The clinical implication of these findings will be further discussed.

Biomechanical Analysis of the Influence of SACH Foot and Dynamic-Response Foot in Individual With Unilateral Transtibial Amputee During Running

Objective: Amputation of the lower limb due to loss of part of the musculoskeletal structure reduces performance and increases injury during locomotion. The effect of various types of prosthetic feet has been analyzed in several studies during running. The purpose of this study was a biomechanical analysis of the influence of SACH and Dynamic-Response foot on several kinetic variables in the stance phase of running in individuals with unilateral transtibial amputation. Materials & Methods: In this semi-experimental study, 8 left foot transtibial amputees were included in this study using an available or easy sampling method. The target population was unilateral transtibial amputees who were able to run and the available population included left transtibial amputees who were referred to Kosar Rehabilitation Center in Tehran from 2008 to 2012. To adapt to the foot, each foot was used by the subjects for at least one week before the experiment. All subjects participated in 3 running evaluation sessions; 1 session involving the use of their own foot (familiarization session), 1 session involving the use of SACH foot, and 1 session involving the use of Dynamic foot. Only data from the 2 last sessions were used to compare both feet. Each subject runs in 12-meter walkway 3 times at a speed of 2.5 meters per second. The same running speed was chosen for the comparability of kinetic variables. Sport shoes were used to bring the test conditions closer to the actual running conditions. In each session, 3 successful trials were performed so that the foot was in full and perfect contact with the force plate. Kistler force plate and three-dimensional motion analysis Vicon system were used to collect kinetic and kinematic data, respectively. The motion and the force plate data were sampled simultaneously at 200 and 1000 Hz, respectively. The trajectories of the markers and analog data were filtered using the predicted mean square error adaptive filter in version 1.7 of the Vicon software package. The Kinetic variables were generated using the dynamic model of the Vicon Plug-in-Gait. The vertical ground reaction force was normalized for body weight. In the present study, 5 variables were selected for biomechanical analysis of feet. The maximum vertical ground reaction force, power, spring efficiency, ankle moments at the amputated leg, and the symmetry ratio (percentage) of the maximum vertical ground reaction force between the amputated leg and the intact leg were calculated. All values ​​in each trial were averaged for each subject with each foot. A paired t-test and a Wilcoxon test were used to analyze the data based on normality (P ≤0.05). Results: In examining the normality of the data distribution, the results showed that the data of maximum power absorption of the ankle with the SACH foot and the maximum power absorption of the hip with the Dynamic-Response foot did not have a normal distribution and other variables had a normal distribution. The results of paired t-test and Wilcoxon showed that Spring Efficiency and Maximum Plantar Flexion were significantly different between the SACH and Dynamic-Response feet (P ≤0.05). The Spring Efficiency was greater with Dynamic-Response foot than the SACH foot (P =0.05), although the Maximum Plantar Flexion with the SACH foot was greater than Dynamic-Response foot (P =0.05). While there is no statistical difference between the maximum vertical ground reaction force, maximum power absorption and generation in the ankle, maximum power absorption and generation in the knee, maximum power absorption and generation in the hip, maximum dorsiflexion moment, and the symmetry ratio (percentage) of the maximum vertical ground reaction force between the amputated leg and the intact leg. Conclusion: The results of the study showed that the spring efficiency with Dynamic-Response foot was greater than SACH foot and closing to the spring efficiency of a normal foot. With this perspective, the Dynamic-Response foot has more natural performance than the SACH foot.

Development of software for performing acoustic time reversal with multiple inputs and outputs

At Brigham Young University, acoustic time reversal experiments are conducted in solids and fluid media. The experimental setup involves synchronized generation and acquisition hardware. The synchronized hardware allows for multi-channel generation, and in some cases, multi-channel acquisition of time reversal focusing. A LabVIEW application has been compiled to increase ease of use and repeatability for the students conducting experiments. Forward and backward steps of time reversal are conducted through this simple user interface. The software is also able to control a 2D positioning system that allows for the measurement of the spatial extent of a time reversal focus. Modifications to traditional time reversal processing, such as inverse filtering and one-bit processing, may be easily implemented in the software. This presentation describes the hardware and software that help to facilitate time reversal research. Ideas from this presentation may help others develop time reversal data acquisition systems.

Third order inverse multifunction filter employing MOS resistors and capacitors

AbstractThis paper presents a systematic approach for the realization of multifunction filter that includes third order inverse low pass filter (ILPF), band pass filter (IBPF), and high pass filter (IHPF) using two Operational Transresistance Amplifiers (OTRAs), MOS resistors, and few number of capacitors. An operational activity of inverse filter configuration (IFC) can be easily realized by proper selection of switches. In ideal case, third order of the filter characterizes a total roll‐off of 60 dB/decade but the proposed design offers a roll‐off in the range of 48.09 dB/decade to 57.74 dB/decade which may arises due to passive component tolerance and some design parameters. The proposed design brings an improvement in roll‐off around 20%–44% in comparison to existing literatures. The multifunction filter frequency response (ILPF, IBPF, and IHPF) is observed by using PSPICE simulation in which the core of the filter “OTRA” is integrated with 180 nm Taiwan Semiconductor Manufacturing Company (TSMC) CMOS technology parameter. In addition to simulation results, hardware implementation of the proposed filter configuration validates the theoretical aspect of filter design.

An Inverse-Filter-Based Method to Locate Partial Discharge Sources in Power Transformers

Partial discharge (PD) occurrence in power transformers can lead to irreparable damage to the power network. In this paper, the inverse filter (IF) method to localize PDs in power transformers is proposed. To the best of the authors’ knowledge, this is the first time that the inverse filter method has been used to localize PD sources in the electromagnetic regime. The method comprises two phases: the forward phase and the backward or backpropagation phase. In the forward phase, the waveform emitted from the PD source is recorded with one or several sensors. In the backward phase, the recorded signal is transformed into the frequency domain, inverted, transformed back into the time domain, and then back injected into the medium. Finally, a suitable criterion is used to localize the PD source. The efficiency of the proposed IF method is assessed considering different scenarios. It is shown that, for the considered configurations, the proposed IF method outperforms the classical time-reversal technique.

Inverse Analog Filters: History, Progress and Unresolved Issues

This paper traces the history of the evolution of inverse analog filters (IAF) and presents a review of the progress made in this area to date. The paper, thus, presents the current state-of-the art of IAFs by providing an appraisal of a variety of realizations of IAFs using commercially available active building blocks (ABB), such as operational amplifiers (Op-amp), operational transconductance amplifiers (OTA), current conveyors (CC) and current feedback operational amplifiers (CFOA) as well as those realized with newer active building blocks of more recent origin, such as operational transresistance amplifiers (OTRA), current differencing buffered amplifiers (CDBA) and variants of current conveyors which, although not available as off-the-shelf ICs yet, can be implemented as complementary metal–oxide–semiconductors (CMOS) or be realized in discrete form using other commercially available integrated circuits (IC). In the end, some issues related to IAFs have been highlighted which need further investigation.

Feature enhancement method of rolling bearing acoustic signal based on RLS-RSSD

The bearing acoustic signal is interfered by reflected sounds and background noises, resulting in a low signal-to-noise ratio (SNR). To address this problem, this paper proposes a feature enhancement method that combines recursive least squares (RLS) with resonance-based sparse signal decomposition (RSSD) into the RLS-RSSD method. First, the RLS method is used as the inverse filter to remove the reverberation as well as reduce the interference of the late reflected sound on the direct signal, then RSSD and wavelet denoising are used to eliminate aperiodic component in the low and high frequency bands. The signals are synthesized based on the amplitudes of different frequency signals, and finally, the bearing fault is determined by envelope spectrum analysis. The results of the simulation data, experimental data, and field application data analysis indicate that the frequency of bearing defects can be accurately extracted by the proposed method.

Medical image fusion based on local Laplacian decomposition and iterative joint filter

AbstractPrevious multi‐modal medical image fusion methods have suffered from color distortion, blurring, and noise. To address these problems, we propose a method for integrating the information contained in functional and anatomical medical images. In the proposed method, multi‐scale image representation of input images is produced by local Laplacian filtering. The rgb2ycbcr algorithm and iterative joint filters are then used to produce fused approximate images. The residual images are divided into regions of interest and noninterest regions, and then a local energy maximization scheme and local energy average scheme are used to combine these regions. Fused interest areas and fused noninterest areas are combined to produce fused residual images. Finally, an inverse local Laplacian filter is used as a reconstruction tool to produce a fused image. Experimental results indicated that our method has a distinct advantage over existing state‐of‐the‐art algorithms in terms of vision quality and objective metrics.

Multi-scale residual network-based image restoration

All Image restoration technology has undergone extensive research. For image degradation, inverse filtering was proposed in the last century. Then Helstrom proposed a Wiener filtering algorithm. In recent years, the convolutional neural network has promoted the further development of image restoration technology. The coarse-to-fine multi-scale residual network Multiscale Deblur Net (MDN) used in this paper is stable in operation, simple in structure, and easy to train. It has a good deblurring ability for motion-blurred images by testing in the GO_PRO dataset.

Signal-to-Noise Ratio Improvement for Multiple-Pinhole Imaging Using Supervised Encoder–Decoder Convolutional Neural Network Architecture

Digital image devices have been widely applied in many fields, such as individual recognition and remote sensing. The captured image is a degraded image from the latent observation, where the degradation processing is affected by some factors, such as lighting and noise corruption. Specifically, noise is generated in the processing of transmission and compression from the unknown latent observation. Thus, it is essential to use image denoising techniques to remove noise and recover the latent observation from the given degraded image. In this research, a supervised encoder–decoder convolution neural network was used to fix image distortion stemming from the limited accuracy of inverse filter methods (Wiener filter, Lucy–Richardson deconvolution, etc.). Particularly, we will correct image degradation that mainly stems from duplications arising from multiple-pinhole array imaging.

RESEARCH ON STOCHASTIC FUZZY DIFFERENTIAL EQUATIONS IN MULTIPLE BLURRED IMAGE REPAIR MODELS

This paper aims to study the processing and repairing methods of blurred images, promote the development of partial differential equations in the field of image processing, and expand the application of stochastic fuzzy differential equations in the field of image processing and repair. This study starts with a typical blurred image repair method. First, a comparative analysis of several common blurred image repair methods including Wiener filtering restoration, inverse filtering restoration, and Lucy–Richardson (L-R) filtering restoration is performed. Second, based on the linear partial differential equation learning model (LPDE), the concept of fuzzy integral is introduced, and an improved stochastic fuzzy partial differential equation learning model (SFCPDE) is proposed. The effect of the learning model before and after improvement on blurred color image processing is compared and analyzed. Finally, based on the total variation (TV) blurred image repair algorithm, an improved TV blurred image repair algorithm is proposed. The comparison and analysis of the repair effects of several blurred image repair algorithms are performed. The results show that there are obvious differences in the repairing methods with or without noise. Inverse filtering works best when there is no noise. L-R filtering has the disadvantage of amplifying noise. Compared with LDPE, the training speed of SFCPDE is significantly improved, and the training error is less than LDPE. The SFCPDE learning model performs better in the processing of blurred color images. After 10 iterations, the improved TV algorithm is significantly better than the TV algorithm and the CDD algorithm in repairing blurred images. The PSNR value of the TV algorithm and the curvature-driven diffusion (CDD) algorithm after 10 iterations corresponds to about 60% of the PSNR value of the improved algorithm. The algorithms and models of stochastic fuzzy partial differential equations proposed in this paper have great application potential in the processing and repair of multiple blurred images.