Two-dimensional Gaussian Filter Research Articles

Stitching interferometry of cylindrical surface

High resolution and high precision are advantages of measuring cylindrical objects employing stitching interferometry. However, due to errors in the cylinder position in a measurement procedure, it is difficult to ensure the accuracy of a macroscopic shape contour and surface waviness contour of the workpiece of the stitching results. To overcome this problem, we proposed a new strategy of stitching interferometry for cylindricity calibration. The measuring process is divided into two parts - to measure the macroscopic shape and waviness contour, respectively. Finally, the two measurement results are merged to produce an accurate and complete 360° form map. Besides, we build a two-dimensional Gaussian filter weighting function for a cylindrical profile according to its special shape characteristic. To express the stitching results more precisely, we provide the uncertainty map and power spectral density of the stitching results. An experiment is carried out by taking a ceramic plug gage as the workpiece. The results demonstrate the excellent performance of our method in analyzing the characteristic of the cylindrical profile and show good agreement with such by using cylindricity measuring instruments.

Vignetting Correction Based on a Two-Dimensional Gaussian Filter With Harmony for Area Array Sensors

Vignetting is the main factor causing uneven brightness in an image due to the inherent characteristics of the camera sensor. In radiometric correction-based remote sensing sensors, vignetting can lead to uncomparable radiation signals within and between images, and in the processing of remote sensing images, it leads to an unbalanced color when images are mosaiced. Due to distortions of optical devices, uneven response of detectors and other factors, it is difficult to extract the vignetting from complex reference images and correct it accurately. In this study, a low-pass Gaussion filter was selected to extract the vignetting from reference image, and the standard deviation (STD) and mean of the reference images were used as the factor of harmony to evaluate the strength of the filter for attaining optimal vignetting background. In experiments, the method proposed was compared with polynomial fitting method and general Gaussian filter mothed. The results show that Gaussian filter with harmony method achieves the best effect of vignetting correction compared with the other two methods.

SAR Image Denoising Using an Improved Adaptive Bitateral Filter

Synthetic aperture radar (SAR) images are inherently affected by multiplicative speckle noise. The presence of speckle damages radiometric resolution, at the same time, it hampers the human interpretation and scene analysis for SAR images. On the base of studying and analyzing the mathematical model of the bilateral filter, the paper proposed a modified adaptive bilateral filter (MABF). First, it separates non-independent two-dimensional Gaussian filter into two independent one-dimensional Gaussian filter, which improves the operation speed greatly. Then through the effective noise parameter estimation, it adaptively selects optimal parameters, which improves the filtering effect. The real SAR image data is used to test the presented method and the experimental results verify that MABF is feasible and effective.

Determinants of Contrast Sensitivity for the Tumbling E and Landolt C

To compare the object spatial frequencies that underlie contrast sensitivity for the tumbling E and Landolt C across a range of optotype sizes and under conditions biased toward the magnocellular (MC) and parvocellular (PC) pathways. Contrast thresholds of two visually normal observers were measured using tumbling E optotypes that were either low-pass filtered or high-pass filtered with a two-dimensional Gaussian filter. Optotypes were presented using steady-pedestal and pulsed-pedestal paradigms to target the MC and PC pathways, respectively. Object frequencies essential for orientation judgments of the tumbling E were derived from plots of log contrast threshold vs. log filter cutoff frequency, and results were compared with those obtained previously for the Landolt C under identical testing conditions. The object frequency used to judge the orientation of the tumbling E increased systematically with increasing target angular subtense, and the effect of target size differed depending on whether performance was mediated by the inferred MC or PC pathway. The overall pattern of results was similar for the tumbling E and Landolt C, but there was generally less dependence of object frequency on target angular subtense for the tumbling E. The tumbling E and Landolt C are not equivalent in terms of the object frequencies that mediate orientation judgments. However, both optotypes show scale-dependent changes in object frequency, particularly under test conditions that favor the PC pathway. The scale dependence of these broadband optotypes can pose a challenge in interpreting test results using these targets. A potential solution is to use spatially filtered optotypes with limited, known object frequency content.

Source Camera Identification for Heavily JPEG Compressed Low Resolution Still Images*

In this research, we examined whether fixed pattern noise or more specifically Photo Response Non-Uniformity (PRNU) can be used to identify the source camera of heavily JPEG compressed digital photographs of resolution 640 x 480 pixels. We extracted PRNU patterns from both reference and questioned images using a two-dimensional Gaussian filter and compared these patterns by calculating the correlation coefficient between them. Both the closed and open-set problems were addressed, leading the problems in the closed set to high accuracies for 83% for single images and 100% for around 20 simultaneously identified questioned images. The correct source camera was chosen from a set of 38 cameras of four different types. For the open-set problem, decision levels were obtained for several numbers of simultaneously identified questioned images. The corresponding false rejection rates were unsatisfactory for single images but improved for simultaneous identification of multiple images.

Regional Cerebral Blood Flow During Script-Driven Imagery in Childhood Sexual Abuse-Related PTSD: A PET Investigation

The purpose of this study was to determine whether anterior limbic and paralimbic regions of the brain are differentially activated during the recollection and imagery of traumatic events in trauma-exposed individuals with and without posttraumatic stress disorder (PTSD). Positron emission tomography (PET) was used to measure normalized regional cerebral blood flow (CBF) in 16 women with histories of childhood sexual abuse: eight with current PTSD and eight without current PTSD. In separate script-driven imagery conditions, participants recalled and imagined traumatic and neutral autobiographical events. Psychophysiologic responses and subjective ratings of emotional state were measured for each condition. In the traumatic condition versus the neutral control conditions, both groups exhibited regional CBF increases in orbitofrontal cortex and anterior temporal poles; however, these increases were greater in the PTSD group than in the comparison group. The comparison group exhibited regional CBF increases in insular cortex and anterior cingulate gyrus; increases in anterior cingulate gyrus were greater in the comparison group than in the PTSD group. Regional CBF decreases in bilateral anterior frontal regions were greater in the PTSD group than in the comparison group, and only the PTSD group exhibited regional CBF decreases in left inferior frontal gyrus. The recollection and imagery of traumatic events versus neutral events was accompanied by regional CBF increases in anterior paralimbic regions of the brain in trauma-exposed individuals with and without PTSD. However, the PTSD group had greater increases in orbitofrontal cortex and anterior temporal pole, whereas the comparison group had greater increases in anterior cingulate gyrus.