Gaussian Low-pass Filter Research Articles

Distribution theory approach to implementing directional acoustic sensors

The objective of directional acoustic sensors is to provide high directivity while occupying a small amount of space. An idealized point sensor achieves this objective from a knowledge of the spatial partial derivatives of acoustic pressure at a point in space. Direct measurement of these derivatives is difficult in practice. Consequently, it is expedient to come up with indirect methods. The use of pressure sensors to construct finite-difference approximations is an example of such a method. This paper utilizes the theory of distributions to derive another indirect method for estimating the various spatial partial derivatives of the pressure. This alternate method is then used to construct a multichannel filter which processes the acoustic pressure by mean of three-dimensional integral transforms throughout a 6epsilon-length cube centered at the origin. The output of the multichannel filter is a spatially and temporally filtered version of the pressure at the origin. The temporal filter is a lowpass Gaussian filter whose bandwidth is inversely proportional to epsilon. Finally, the lattice method for numerical multiple integration is utilized to develop a discrete-spatial version of the multichannel filter.

Perceived Blur in Naturally Contoured Images Depends on Phase

Perceived blur is an important measure of image quality and clinical visual function. The magnitude of image blur varies across space and time under natural viewing conditions owing to changes in pupil size and accommodation. Blur is frequently studied in the laboratory with a variety of digital filters, without comparing how the choice of filter affects blur perception. We examine the perception of image blur in synthetic images composed of contours whose orientation and curvature spatial properties matched those of natural images but whose blur could be directly controlled. The images were blurred by manipulating the slope of the amplitude spectrum, Gaussian low-pass filtering or filtering with a Sinc function, which, unlike slope or Gaussian filtering, introduces periodic phase reversals similar to those in optically blurred images. For slope-filtered images, blur discrimination thresholds for over-sharpened images were extremely high and perceived blur could not be matched with either Gaussian or Sinc filtered images, suggesting that directly manipulating image slope does not simulate the perception of blur. For Gaussian- and Sinc-blurred images, blur discrimination thresholds were dipper-shaped and were well-fit with a simple variance discrimination model and with a contrast detection threshold model, but the latter required different contrast sensitivity functions for different types of blur. Blur matches between Gaussian- and Sinc-blurred images were used to test several models of blur perception and were in good agreement with models based on luminance slope, but not with spatial frequency based models. Collectively, these results show that the relative phases of image components, in addition to their relative amplitudes, determines perceived blur.

Autofocusing in optical scanning holography

We present autofocusing in optical scanning holography (OSH) with experimental results. We first record the complex hologram of an object using OSH and then create the Fresnel zone plate (FZP) that codes the object constant within the depth range of the object using Gaussian low-pass filtering. We subsequently synthesize a real-only spectrum hologram in which its phase term contains information about a distance parameter. Finally, we extract the distance parameter from the real-only spectrum hologram using fringe-adjusted filtering and the Wigner distribution. Using the extracted distance parameter, we reconstruct a three-dimensional image of the object from the complex hologram using digital convolution, which bypasses the conventional blind convolution to reconstruct a hologram. To the best of our knowledge, this is the first report with experimental results that autofocusing in OSH is possible without any searching algorithm or tracking process.

Algorithm for converting full-parallax holograms to horizontal-parallax-only holograms

We propose an algorithm that converts a full-parallax hologram to a horizontal-parallax-only (HPO) hologram for 3D display. We first record a full-parallax hologram of an object. Subsequently, we filter the hologram with a Gaussian low-pass filter and a fringe-matched filter along the vertical direction. The final filtered output becomes an HPO hologram. To the best of our knowledge, this is the first algorithm proposed for converting full-parallax holographic information to HPO-holographic information.

Recent climate change in Japan – spatial and temporal characteristics of trends of temperature

Abstract. In this paper temperature series of Japan were statistically analysed in order to answer the question whether recent climate change can be proved for Japan; the results were compared and discussed with the global trends. The observations in Japan started for some stations in the 1870s, 59 stations are available since 1901, 136 stations since 1959. Modern statistical methods were applied, such as: Gaussian binominal low-pass filter (30 yr), trend analysis (linear regression model) including the trend-to-noise-ratio as measure of significance and the non-parametric, non-linear trend test according to MANN (MANN's Q). According to the results of the analyses, climate change in Japan is clearly shown for temperature over the 100 yr (1901–2000): Annual mean temperatures increased at all stations from 0.35 (Hakodate) to 2.95°C (Tokyo). The magnitude of climate change is illustrated to increase over the recent period 1976–2000. Seasonally, the strongest warming trends were observed for winter temperatures and also increasing temperature trends prevailed in summer, with the exception of slightly decreasing trends at only four stations.

Color interpolation by expanding a gradient method

This paper proposes a color filter array interpolation method, which expands the preceding gradient based scheme by adopting Gaussian low-pass filter. It starts from the assumption that high frequency components of the green plane in an image are almost the same as those of the red or blue planes in the same image. We identify that the conventional gradient method can make use of this idea and can be expanded by Gaussian low-pass filter to enhance its performance. To determine the reasonable mask size and the appropriate Gaussian sigma value, various values are tested with sample images, and used later to interpolate the green plane for other test images in the proposed method. Afterward, red and blue plane interpolations are performed, and directional median processing is applied along the flat edge lines. This process can effectively suppress false colors introduced during the interpolation of color planes. The proposed method provides a reasonable visual quality and generally higher peak-signal-to-noise-ratio compared to existing methods.

Counting eosinophils in bronchoalveolar lavage fluid images with fuzzy methodology

This paper proposes a new fuzzy approach to count eosinophils, as a measure of inflammation, in bronchoalveolar lavage fluid images, provided by digital camera through microscope. We use fuzzy cluster analysis and fuzzy classification algorithm to determine the number of objects in an image. For this purpose, a fuzzy image processing procedure consisting of five main stages is presented. The first stage is pre-highlighting the objects in the images by using an image pre-processing method for enhancement, which is sharpening the image with the Laplaian high pass filter in order to have acceptable contrast in the image. The second stage is segmentation by clustering with fuzzy c-mean algorithm for portioning. In this stage the clustered data are the rough symbols of objects in the image containing noise. In the third step, first, a Gaussian low pass filter is used for noise reduction. Then, a contrast adoption in the image is done by modifying the membership functions in the image [H.R. Tizhoosh, G. Krell, B. Michaelis, Knowledge-based enhancement of megavoltage images in radiation therapy using a hybrid neuro-fuzzy system, Image and Vision Computing 19(July) (2000) 217–233]. Object recognition, the fourth stage, will be done by using fuzzy labeling for the objects in the image, using a fuzzy classification method. The number of labeled images shows the number of eosinophils in an image which is an index for diagnosing inflammation. The last stage is tuning parameters and verification of the system performance by using a feed forward Neural Network.

Interactive Cosmetic Makeup of a 3D Point-Based Face Model

We present an interactive system for cosmetic makeup of a point-based face model acquired by 3D scanners. We first enhance the texture of a face model in 3D space using low-pass Gaussian filtering, median filtering, and histogram equalization. The user is provided with a stereoscopic display and haptic feedback, and can perform simulated makeup tasks including the application of foundation, color makeup, and lip gloss. Fast rendering is achieved by processing surfels using the GPU, and we use a BSP tree data structure and a dynamic local refinement of the facial surface to provide interactive haptics. We have implemented a prototype system and evaluated its performance.

Amplitude modulation filtering of FM-to-AM conversion due to the focusing grating of LMJ

FM-to-AM conversion is an important issue for high power lasers such as the Laser MegaJoule. Indeed temporal intensity modulation may prevent a good ignition of the target. FM is necessary to achieve optical smoothing: phase modulation broadens the spectrum and the different generated wavelengths will create different speckle patterns thanks to dispersion systems (gratings) that spatially average the focal spot on the target. We show in this paper that dispersion and focusing systems linearly filter intensity modulations by averaging due to time delay introduced by the gratings. For the LMJ configuration this filter is equivalent to a Gaussian low-pass filter with a 7GHz 3dB-bandwidth.

Analysis of free turbulent steam jet by processing of IR-images

This paper presents an IR-imaging technique to visualize a turbulent steam flow. Instantaneous, time-averaged, Gaussian-smoothed and non-linear filtered IR-images are compared. Wavelet threshold is applied to separate the coherent part of the instantaneous intensity field from the incoherent part. The averaged image has been smoothed with a non-linear filter that preserves the energy content of the thermal image better than the Gaussian low-pass filtering. High frequency wavelet components of the processed IR-images highlight the differences of the applied filtering techniques. Reconstruction the flow pattern from these components shows the directional orientation of the instantaneous and averaged flows.

Global warming possibly linked to an enhanced risk of suicide: Data from Italy, 1974–2003

Background The global increase in surface temperature (known as global warming) was found to impact on mortality through ill health, particularly among the elderly and in summer. This study sets out to explore the impact of global warming on suicide mortality, using data from Italy. Methods Monthly data on suicide mortality and temperature were obtained for a 30-year period (from January 1974 to December 2003), and the relation between them was investigated using the Gaussian low-pass filter, linear correlation analysis and rank analysis. Results For males, increasing anomalies in monthly average temperatures associated to a higher monthly suicide mean from May to August and, to a lower extent, in November and December. In January, on the other hand, increasing anomalies in monthly average temperatures appeared to be coupled to a lower number of suicides. For females, the links between temperature and suicides are less consistent than for males, and sometimes have a reverse sign, too. Limitations Data could not be analyzed according to age, since this information was not available across the whole time interval. The use of monthly data, instead of daily data (unavailable), is another major limitation of this study. Conclusions An improvement in the ability of communities to adjust to temperature changes by implementing public health interventions may play an important part in preserving the wellness of the general population, and also in limiting the worst consequences of suicidal behaviour.

Comparison of Wavefront Reconstructions With Zernike Polynomials and Fourier Transforms

To make a direct comparison between Fourier and Zernike reconstructions of ocular wavefronts using a newly available analytical theory by which Fourier coefficients can be converted to Zernike coefficients and vice versa. Noise-free random wavefronts were simulated with up to the 15th order of Zernike polynomials. For each case, 100 random wavefronts were simulated separately. These wavefronts were smoothed with a low-pass Gaussian filter to remove edge effects. Wavefront slopes were calculated, and normally distributed random noise was added within the circular area to simulate realistic Shack-Hartmann spot patterns. Three wavefront reconstruction methods were performed. The wavefront surface error was calculated as the percentage of the input wavefront root mean square. Fourier full reconstruction was more accurate than Zernike reconstruction from the 6th to the 10th orders for low-to-moderate noise levels. Fourier reconstruction was found to be approximately 100 times faster than Zernike reconstruction. Fourier reconstruction always makes optimal use of information. For Zernike reconstruction, however, the optimal number of orders must be chosen manually. The optimal Zernike order for Zernike reconstruction is lower for smaller pupils than larger pupils. Fourier full reconstruction is faster and more accurate than Zernike reconstruction, makes optimal use of slope information, and better represents ocular aberrations of highly aberrated eyes.

The 3-D alignment of objects in dynamic PET scans using filtered sinusoidal trajectories of sinogram

In this study, our goal is to employ a novel 3-D alignment method for dynamic positron emission tomography (PET) scans. Because the acquired data (i.e. sinograms) often contain noise considerably, filtering of the data prior to the alignment presumably improves the final results. In this study, we utilized a novel 3-D stackgram domain approach. In the stackgram domain, the signals along the sinusoidal trajectory signals of the sinogram can be processed separately. In this work, we performed angular stackgram domain filtering by employing well known 1-D filters: the Gaussian low-pass filter and the median filter. In addition, we employed two wavelet de-noising techniques. After filtering we performed alignment of objects in the stackgram domain. The local alignment technique we used is based on similarity comparisons between locus vectors (i.e. the signals along the sinusoidal trajectories of the sinogram) in a 3-D neighborhood of sequences of the stackgrams. Aligned stackgrams can be transformed back to sinograms (Method 1), or alternatively directly to filtered back-projected images (Method 2). In order to evaluate the alignment process, simulated data with different kinds of additive noises were used. The results indicated that the filtering prior to the alignment can be important concerning the accuracy.

Lower slab boundary in the Japan subduction zone

We have successfully detected the lower boundary of a subducting slab. The successive imaging of the lower slab boundary beneath northeastern (NE) Japan is attained by receiver function (RF) depth conversion analysis using a recent 3D tomographic velocity model. We use waveforms from 249 teleseismic events collected by Hi-net and J-array short-period stations in NE Japan. RFs are calculated through frequency domain division of radial components by vertical ones with a water level of 0.001 and a 1.0 Hz low-pass Gaussian filter. Assuming that all later phases in the radial RFs are due to Ps phases converted at discontinuities beneath stations, we calculate depth-converted RFs, mapped onto the cross-section with the CCP (common conversion point) stacking. In a cross section, the slab surface and the oceanic Moho can be imaged down to 120 km depth. For the greater depths, the RF amplitudes corresponding to them cannot be seen, because, in the oceanic crust, basalt would be completely metamorphosed to eclogite below this depth. The lower boundary of the Pacific slab can also be traced down to 200 km depth or more. It is parallel to the slab surface and the oceanic Moho, and the thickness between the slab surface and the lower boundary is ∼ 80 km. Finally, we estimate a top-to-bottom slab velocity model that explains the RFs observed at broadband stations with the synthetic RFs. This model exhibits a 13% velocity reduction downwards the lower slab boundary, which would relatively sharp for the base of the thermal boundary layer. Therefore, this sharp discontinuity is presumably considered to be the subducting G (Gutenberg) discontinuity that is formed by the change of the amount of H 2O (water), meaning that the G discontinuity is the chemical boundary at the bottom of the oceanic lithosphere. The G discontinuity depth is controlled by the potential temperature of the asthenospheric mantle beneath the mid-ocean ridge, and hence the observed thickness of 80 km, i.e. the G discontinuity depth, corresponds to 1375 °C in potential temperature when this boundary is formed.

Stiffness‐weighted magnetic resonance imaging

An imaging method is introduced in which the signal in MR images is affected by the stiffness distribution in the object being imaged. Intravoxel phase dispersion (IVPD) that occurs during MR elastography (MRE) acquisitions decreases the signal in soft regions more than in stiff regions due to changes in shear wave amplitude and wavelength. The IVPD effect is enhanced by lowpass filtering the MR k-space data with a circular Gaussian lowpass filter. A processing method is introduced to take the time series of MRE magnitude images with IVPD and produce a final stiffness-weighted image (SWI) by calculating the minimum signal at each pixel from a small number of temporal samples. The SWI technique is demonstrated in phantom studies as well as in the case of a preserved postmortem breast tissue specimen with a stiff lesion created by focused ultrasound ablation to mimic a breast cancer. When free of significant sources of depth-dependent wave attenuation, interference, and boundary effects, SWI is a simple, fast, qualitative technique that does not require the use of phase unwrapping or inversion algorithms for localizing stiff regions in an object.

Glacier mass balance in southern norway modelled by circulation indices and spring‐summer temperatures ad 1781–2000

By stepwise regression analysis the accumulation, ablation, and equilibrium line altitude (ELA) were modelled by circulation indices and spring‐summer temperature on six Norwegian glaciers (Ålfotbreen, Nigardsbreen, Rembesdalsskåka, Storbreen, Hellstugubreen and Gråsubreen). The circulation indices were derived from a gridded monthly mean sea level pressure (MSLP) data set, whereas temperature series were derived from instrumental and proxy data.Analyses showed that accumulation on the western glaciers was strongly related to western airflow perpendicular to the main mountain range releasing precipitation on the glaciers. No other airflow variable significantly improved the regression. For the continental glaciers, circulating air in connection with low pressure systems was also found to be important. This may explain the lack of synchronicity in the glaciers' development in southern Norway during the Holocene. Accumulation was better modelled using the MSLP data set than by using the North Atlantic Oscillation (NAO) index as predictor.The decadal variations of accumulation, ablation, and ELA were analysed by a Gaussian low pass filter. The well‐known abundant accumulation on Norwegian glaciers during the early 1990s turned out to be unprecedented during the entire series (since 1781), whereas the accumulation of the 1960s has not been lower since the early 19th century according to model results. Ablation increased significantly from the mid‐19th century to the 1930s. The ablation maximum during the 1930s has not yet been exceeded. Also the 1930s show extremely high ELA values.

Detailed structure of the upper mantle discontinuities around the Japan subduction zone imaged by receiver function analyses

Abstract High-resolution receiver function (RF) images of the upper mantle structure beneath the Japan Islands are obtained by RF analysis of the P-wave coda portions of 389 teleseismic events observed at 138 high-density broadband stations. We construct RFs through frequency-domain division using a water level of 0.01 and Gaussian low-pass filters of 1.0, 0.5, 0.3, and 0.1 Hz, and produce depth-migrated RFs using the one-dimensional IASP91 velocity model. The RF images clearly resolve the subducting Pacific Plate to a depth of 200 km, and reveal a local 30 km elevation of the 410 km discontinuity within the subducting plate. The 660 km discontinuity is also found to exhibit a broad 50 km depression under the influence of the stagnating slab. From analysis of the frequency dependence of the RFs, the thickness of the 410 km discontinuity is inferred to vary on a relatively local scale, whereas the 660 km transition is sharp throughout the Japan Islands.

A low-power CMOS Bluetooth RF transceiver with a digital offset canceling DLL-based GFSK demodulator

This paper presents a fully integrated 0.18-μm CMOS Bluetooth transceiver. The chip consumes 33 mA in receive mode and 25 mA in transmit mode from a 3-V system supply. The receiver uses a low-IF (3-MHz) architecture, and the transmitter uses a direct modulation with ROM-based Gaussian low-pass filter and I/Q direct digital frequency synthesizer for high level of integration and low power consumption. A new frequency shift keying demodulator based on a delay-locked loop with a digital frequency offset canceller is proposed. The demodulator operates without harmonic distortion, handles up to ±160-kHz frequency offset, and consumes only 2 mA from a 1.8-V supply. The receiver dynamic range is from -78 dBm to -16 dBm at 0.1% bit-error rate, and the transmitter delivers a maximum of 0 dBm with 20-dB digital power control capability.

Effect of image contrast and sharpness on visual search for computer icons

The purpose of the study was to determine the effect of image blur and contrast on the speed of visual search for user interface icons and investigate how the effect is reflected in eye movement parameters. The task of the observer was to search for a target icon from among a rectangular array of distracter icons. A staircase algorithm was used to determine the stimulus presentation time, threshold search time, for which the probability of correct responses was 0.79. Simultaneously, eye-movements were recorded with a video eye-tracker with a sampling rate of 250 Hz. Image sharpness was varied by filtering the stimulus images with a Gaussian low-pass filter. The results showed that with increasing contrast or sharpness search time, number of fixations per search, and fixation duration first decreased, and then became constant at medium levels of contrast or sharpness. These effects were somewhat more pronounced for contrast than for sharpness. Saccade amplitudes were not affected by contrast or sharpness. The results suggest that the perception of user interface icons is quite resistant to small or moderate deterioration of image quality.

홀로그램 정보를 이용한 깊이위치 추출과 3차원 영상인식

물체의 홀로그램은 물체의 깊이위치에 대한 정보뿐 아니라 물체의 깊이분포에 대한 정보도 가지고 있다. 그러나 두 가지 정보는 프린지 패턴(fringe pattern)의 형태로 서로 썩여있어 홀로그램으로부터 물체의 깊이위치에 대한 정보를 분리해내기 어렵다. 본 논문에서는 물체의 깊이 및 위치분포에 대한 정보를 갖는 단일 결띠 홀로그램(single-sideband hologram)으로부터 물체의 깊이위치에 대한 정보만을 가우시안 저-대역 필터를 이용해 추출해내고 그를 수치적 방법으로 해석해 물체의 깊이위치를 얻어내는 알고리즘을 제안한다. 또한 추출된 깊이위치를 이용하여 물체의 깊이위치에서 홀로그램을 복원해낸다. The hologram of an object contains the information of the object's depth distribution as well as the depth location of the object. However these pieces of information are blended together as a form of fringe pattern. This makes it hard to extract the depth location of the object directly from the hologram. In this paper, I propose a numerical method which separates the depth location information from the single-sideband hologram by gaussian low-pass filtering. The depth location of the object is extracted by numerical analysis of the filtered hologram. The hologram at the object's depth location is recovered by the extracted depth location.