Image Width Research Articles

Measurement of knot width in CT images of Norway spruce (Picea abies [L.] Karst.)—Evaluating the accuracy of an image analysis method

X-ray computed tomography (CT) is an effective scanning technology for imaging inner roundwood features. It is assumed that using this technology for log inspection prior to the first conversion could further optimise raw material utilisation. If the information obtained by CT scanning of a log shall be exploited in an industrial application, automated interpretation of CT images is a necessity. An image analysis method for knot extraction and measurement was tested on CT images of Norway spruce (Picea abies [L.] Karst.) produced by a prototype of a dedicated roundwood CT scanner. Measurement accuracy was evaluated through a comparison of the computer measurements obtained on single CT slices to reference measurements obtained manually on physical log cross-sections that corresponded to the images treated. In a linear regression established from 119 measurement pairs 68% of the variation of the manually measured knot width could be explained by the variation of the computer measurements. Bias and root mean squared error (RMSE) were 1.7mm and 4mm, respectively. Hence the measurements were generally in accordance, but an overestimation of knot width by the computer vision method was observed. An algorithm for removing bright sapwood areas from the CT images—necessary as a preparation for knot segmentation—has been found to fail at images of logs with partly dried sapwood; this problem was identified as the primary reason for the loss of 28% of the measurements originally to be acquired and for the occurrence of erroneous measurements. It should be investigated whether a modification of this algorithm could enhance the performance and accuracy of the method.

Spartan Infrared Camera, a High-Resolution Imager for the SOAR Telescope: Design, Tests, and On-Telescope Performance

ABSTRACTThe Spartan Infrared Camera provides tip-tilt corrected imaging for the SOAR Telescope in the 900–2500 nm spectral range with four 2048 × 2048 HAWAII-2 detectors. The camera has two plate scales: high-resolution () for future diffraction-limited sampling in the H and K bands and wide-field () to cover a 5′ × 5′ field, over which tip-tilt correction is substantial. The design is described in detail. Except for CaF2 field-flattening lenses, the optics are aluminum mirrors to thermally match the aluminum cryogenic-optical box in which the optics mount. The design minimizes the tilt of the optics as the instrument rotates on the Nasmyth port of the telescope. Two components of the gravitational torque on an optic are eliminated by symmetry, and the third component is minimized by balancing the optic. The optics (including the off-axis aspherical mirrors) were aligned with precise metrology. For the detector assembly, Henein pivots are used to provide frictionless, thermally compliant, lubricant-free, and thermally conducting rotation of the detectors. The heat load is 14 W for an ambient temperature of 10°C. Cooling down takes 40 hr. An activated-charcoal getter controls permeation through the large Viton O-ring for at least nine months. We present maps of the image distortion, which amount to tens of pixels at the greatest. The wavelength of the narrowband filters shift with position in the sky. The measured Strehl ratio of the camera itself is 0.81–0.84 at λ1650 nm. The width of the best K-band image was 260 mas in unexceptional seeing measured after tuning the telescope and before moving the telescope. Since images are normally taken after pointing the telescope to a different field, this supports the idea that the image quality could be improved by better control of the focus and the shape of the primary mirror. The instrument has proved to be capable of producing images that can be stitched together to measure faint, extended features and to produce photometry that agree internally to better than 0.01 mag and are well calibrated to 2MASS stars in the range of 12 < K < 16.

Pulse wave imaging of the human carotid artery: an in vivo feasibility study

Noninvasive quantification of regional arterial stiffness, such as measurement of the pulse wave velocity (PWV), has been shown to be of high clinical importance. Pulse wave imaging (PWI) has been previously developed by our group to visualize the propagation of the pulse wave along the aorta and to estimate the regional PWV. The objective of this paper is to determine the feasibility of PWI in the human carotid artery in vivo. The left common carotid arteries of eight (n = 8) healthy volunteers (male, age 27 + 4 years old) were scanned in a long-axis view, with a 10-MHz linear-array transducer. The beam density of the scan was reduced to 16 beams within an imaging width of 38 mm. The frame rate of ultrasound imaging was therefore increased to 1127 Hz at an image depth of 25 mm. The RF ultrasound signals were then acquired at a sampling rate of 40 MHz and used to estimate the velocity of the arterial wall using a 1-D cross-correlationbased speckle tracking method. The sequence of the wall velocity images at different times depicts the propagation of the pulse wave in the carotid artery from the proximal to distal sides. The regional PWV was estimated from the spatiotemporal variation of the wall velocities and ranged from 4.0 to 5.2 m/s in eight (n = 8) normal subjects, in agreement with findings reported in the literature. PWI was thus proven feasible in the human carotid artery, and may be proven useful for detecting vascular disease through mapping the pulse wave and estimating the regional PWV in the carotid artery.

Natural scenes are robust to bubbling

“Random bubbling” was achieved by selecting 5-8 arbitrary points within an image. • Radii for circles centered on these points were chosen to maximize the coverage of the image • Circles could not overlap • No radius could fall below 5% of the image width • Keep only displays providing > 80% coverage. • All circles were uniformly scaled to reach desired level of occlusion (20%, 40%, 60%, 80%) Good Beach Bad Beach 100% visible

Improved sensitivity for the atmospheric infrared sounder instrument

We present infrared spectrometer design options offered through a wave propagation analysis throughout the optical system that would not be known otherwise. A recent inclusion of wave propagation into the atmospheric infrared sounder (AIRS) design model to account for an unanticipated measured spectral line narrowing with wavelength has shown that a wider slit option could have been used on the spectrometer to improve energy throughput. The underlying slit image width that narrowed could have been traded for a wider entrance slit increasing the instrument light sensitivity up to 15%, restoring the original un-narrowed slit width baseline, and recovering the spectral sampling requirement of two detectors per line profile. Of the 11 slits on the AIRS spectrometer, each slit width could have been spectrally tailored to become wider as the dispersed wavelength band increased, leading to a more optimal sounder configuration. We will show the newer suggested AIRS slit array below for future sounder design consideration after first reviewing past results that substantiate the wave propagation model being used.

Spatial anisotropy analyses of subcutaneous tissue layer: potential insights into its biomechanical characteristics

As the intermediate layer between the muscle and skin, the subcutaneous tissue frequently experiences shear and lateral stresses whenever the body is in motion. However, quantifying such stresses in vivo is difficult. The lack of such measures is partly responsible for our poor understanding of the biomechanical behaviors of subcutaneous tissue. In this study, we employ both ultrasound imaging and a novel spatial anisotropy measure - incorporating Moran's I spatial autocorrelation calculations - to investigate the structuromechanical features of subcutaneous tissues within the extremities of 16 healthy volunteers. This approach is based on the understanding that spatial anisotropy can be an effective surrogate for the summative, tensile forces experienced by biological tissue. We found that spatial anisotropy in the arm, thigh and calf was attributed to the echogenic bands spanning the width of the ultrasound images. In both univariable and multivariable analyses, the calf was significantly associated with greater anisotropy compared with the thigh and arm. Spatial anisotropy was inversely related to subcutaneous thickness, and was significantly increased with longitudinally oriented probe images compared with transversely orientated images. Maximum peaks in spatial anisotropy were frequently observed when the longitudinally oriented ultrasound probe was swept across the extremity, suggesting that longitudinal channels with greater tension exist in the subcutaneous layer. These results suggest that subcutaneous biomechanical tension is mediated by collagenous/echogenic bands, greater in the calf compared with the thigh and arm, increased in thinner individuals, and maximal along longitudinal trajectories parallel to the underlying muscle. Spatial anisotropy analysis of ultrasound images has yielded meaningful patterns and may be an effective means to understand the biomechanical strain patterns within the subcutaneous tissue of the extremities.

Quick detection of brain tumors and edemas: A bounding box method using symmetry

A significant medical informatics task is indexing patient databases according to size, location, and other characteristics of brain tumors and edemas, possibly based on magnetic resonance (MR) imagery. This requires segmenting tumors and edemas within images from different MR modalities. To date, automated brain tumor or edema segmentation from MR modalities remains a challenging, computationally intensive task. In this paper, we propose a novel automated, fast, and approximate segmentation technique. The input is a patient study consisting of a set of MR slices, and its output is a subset of the slices that include axis-parallel boxes that circumscribe the tumors. Our approach is based on an unsupervised change detection method that searches for the most dissimilar region (axis-parallel bounding boxes) between the left and the right halves of a brain in an axial view MR slice. This change detection process uses a novel score function based on Bhattacharya coefficient computed with gray level intensity histograms. We prove that this score function admits a very fast (linear in image height and width) search to locate the bounding box. The average dice coefficients for localizing brain tumors and edemas, over ten patient studies, are 0.57 and 0.52, respectively, which significantly exceeds the scores for two other competitive region-based bounding box techniques.

Absolute transmission and separation properties of the gas-filled recoil separator RITU

The absolute transmission values of the RITU gas-filled recoil separator have been measured for several fusion evaporation products. Three different beams and several targets were used to create fusion evaporation residues in mass region A=170–190 mainly in neutron evaporation channels. Measured absolute transmission values from around 7% up to round about 90% have been observed for very asymmetric and symmetric reactions, respectively. For the reactions studied it was observed that the angular spread of products after the target and the angular acceptance of RITU determine the transmission probability relatively accurately. Magnetic rigidities and equilibrium charges of the product ions were seen to systemically decrease and increase, respectively, with increasing gas pressure. The comparison of observed equilibrium charges to various formulae is carried out. Clear minima of image width were found in case of asymmetric reactions as a function of gas pressure. Effects of the position of an additional movable beam stopper and the field strength of the first quadrupole magnet on transmission have been studied and are reported.

WE‐E‐BRB‐07: EPID Based Verification of Delivered Fluence for VMAT with High Angular Resolution

Purpose: In VMAT, the dose rate, MLC position, and gantry angle change simultaneously, it is important they follow their predefined trajectories to ensure correct dose delivery. Our purpose is to develop an efficient VMAT QA strategy using EPID that is capable of quantifying delivery errors per gantry angle. Methods: For the QA procedure, portal images are acquired continuously during VMAT delivery. The plan is modified automatically so that the two most inferior MLC leaf pairs are open at all control points. A custom built phantom is positioned via image guidance to be visible in all projections of the opened leaf pairs, and is used to measure the angular fraction through which each portal image is acquired. Expected values of delivered MU and beginning and ending MLC positions are calculated from the plan using the measured start and stop gantry angles per image. They are used to compute a predicted detector response using the treatment planning software (Portal Dosimetry, Varian). The calculated portal response is further analyzed against the EPID images in 3D. We performed the QA procedure for a clinical VMAT 170° arc. Results: The mean gantry angle and angular width of each portal image measured using the phantom was shown to be accurate to within 0.06°±0.14° and 0.59°±0.36°, respectively. Conversely, the angle recorded with each portal image had a larger error of 1.04°±0.84°. QA analysis consisted of projecting the measured and predicted data into 3 planes: leaf motion axis vs. cross leaf axis, leaf motion vs. gantry angle, and cross leaf vs. gantry. In each plane intensities are defined by dose, dose rate, MLC positioning, and gantry angle, thereby allowing verification of all essential machine parameters. Conclusions: Accurate and efficient VMAT QA can be performed using EPID and customized phantom and software that provides verification of all plan parameters.

Electrolocation with an electric organ discharge waveform for biomimetic application

Weakly electric fish use electric organ discharge (EOD) and their electroreceptors to identify prey, explore their surroundings, and communicate with other members of the same species. They are specialized in active electrolocation using a self-generated electric field, and they can sense distortion of their self-generated electric field caused by a target object. Electric fish have many electrosensors on the surface of their body, and the sensor readings from the electroreceptors form an electric image. A correlation exists between features of the electric images and characteristics of a target object. In estimating the location of a target object, the intensity, width, and slope of the electric image must be considered. In this article, we suggest that periodic EOD signals are helpful to extract localization features from noisy electrosensory signals. Cross-correlation between an efference copy signal and sensory signals in the waveform can produce filtered signals in the temporal domain. For a biomimetic fish robot, we can use two-phase filtering: noise-filtering with cross-correlation in the temporal axis and additional filtering in the rostrocaudal spatial axis. This spatiotemporal filtering can effectively remove noise, thus making it possible to obtain accurate localization features of a target object in an underwater environment.

High-resolution, background-free, time-to-space conversion by collinearly phase-matched sum-frequency generation

We report the first demonstration, to our knowledge, of time-to-space conversion of 1.55 μm femtosecond optical pulses using nondegenerate, collinearly phase-matched sum-frequency generation. A quasi-monochromatic and background-free output signal spanning a time window of 35 ps and with a pulse image width of 350 fs was achieved. The resulting serial-to-parallel resolution factor of 100 demonstrates the potential for all-optical complete frame demultiplexing of a 1 Tbit/s optical time-division multiplexing bit stream.

Effect of frequency bandwidth on interaural cross-correlation in relation to sound image width of reproduced sounds of a violin

This article discusses the effect of frequency bandwidth on the maximum absolute value of interaural cross-correlation coefficient (IACC) in relation to sound image width (also known as auditory source width, ASW). Subjective experiments concerning sound image width were performed using reproduced sounds of a violin. This article shows that separation into 1/24 and more octave bands and averaging IACC values of these frequency bands leads to a higher correlation to sound image width than IACC in broader frequency bands. Moreover the average of 1/ n octave bands of the temporal deviation of interaural time differences and interaural level differences could be confirmed as measures correlating with sound image width.

Objective yarn bulk measurement through image analysis

A novel objective yarn bulk measurement method has been developed through image analysis technique. Two orthogonal images are taken from the same part of a yarn and then transformed into gray scale. Each gray scale image is further processed separately by extracting the yarn image from background with the help of intensity histogram using adaptive threshold. This gives rise to a binary image which is used as input for the second part of the algorithm measuring yarn volume. The processing on the input image starts with omitting the long rare loops, considered as noise, by morphological operations. This is followed by measuring the width of the two orthogonal images pixel by pixel along the yarn. Finally, the total volume of the yarn is ascertained by integrating the volume of all the individual imaginary ovals with their two diameters replaced by the two widths of orthogonal images at the corresponding pixel.

ウェーブレット変換領域におけるシームカービング

Content-aware image resizing techniques have become more important with the development of device technology. Although the seam carving method produces high-quality resized images, it requires high computational complexity. In this paper, we propose a novel content-aware image resizing technique that performs the seam carving method in the wavelet transform domain. This approach reduces the computational complexity of image resizing. To avoid breaking the spatial continuity of an image, we reduce the image width by scaling the seam width down instead of carving it out. In addition, the decomposition level is decreased adaptively to avoid distortion. We demonstrate how our method is faster than the seam carving method at producing resized images that retain the important regions.

Systematic error analysis and compensation for high accuracy star centroid estimation of star tracker

Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the consideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of centroid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid location and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel- and 5-pixel-windows’ centroid estimation are less than 2×10−3 pixels and 2×10−4 pixels respectively.

Automated anatomical demarcation using an active shape model for videofluoroscopic analysis in swallowing

The current gold standard method in the clinical assessment of swallowing is the visual inspection of videofluoroscopic frames. Specific clinical measurements are estimated based on various anatomical and bolus positional information with respect to time (or frame number). However, due to the subjective nature of visual inspection clinicians face intra- and inter-observer repeatability issues and bias when making these estimations. The correct demarcations of reference lines highlighting the positions of important anatomical landmarks would serve as a visual aid and could also be used in conjunction with bolus detection methods to objectively determine these desirable measurements. In this paper, we introduce and test the reliability of applying a 16-point Active Shape Model as a deformable template to demarcate the boundaries of salient anatomical boundaries with minimal user input. A robust end and corner point detection algorithm is also used to provide image information for the suggested movement of the template during the fitting stage. Results show the model deformation constraints calculated from a training set of images are clinically coherent. The Euclidean distances between the fitted model points against their corresponding target points were measured. Test images were taken from two different data sets from frames acquired using two different videofluoroscopy units. Overall, fitting was found to be more reliable on the vertebrae and inferior points of the larynx compared to the superior laryngeal points and hyoid bone, with the model always fitting the C7 vertebra with discrepancies no higher than a distance of 23 pixels (3.2% of the image width, approximately 7.6 mm).

Four-dimensional matrix Walsh transform for lossless compression of color video

This article presents a coding method for the lossless compression of color video. In the proposed method, four-dimensional matrix Walsh transform (4D-M-Walsh-T) is used for color video coding. The whole n frames of a color video sequence are divided into ‘3D-blocks’ which are image width (row component), image height (column component), image width (vertical component) in a color video sequence, and adjacency (depth component) of n frames (Y, U or V) of the video sequence. Similar to the method of 2D-Walsh transform, 4D-M-Walsh-T is 4D sub-matrices, and the size of each sub-matrix is n. The method can fully utilize correlations to encode for lossless compression and reduce the redundancy of color video, such as adjacent pixels in one frame or different frames of a video at the same time. Experimental results show that the proposed method can achieve higher lossless compression ratio (CR) for the color video sequence.

A model for saturation correction in meteor photometry

In order to correct for the effect of saturation on photometric measurements of meteors, we have developed a numerical model for saturation and apply it to data gathered using two generation III image intensified video systems on two nights (2008 October 31 and 2008 November 6). The two cameras were pointed in the same direction, and the aperture of one camera was set two stops below the aperture of the other. With these conditions, some meteors saturated one camera but not the other (group I); some saturated both cameras (group II); and some did not saturate either of them (group III). A model of meteor saturation has been developed which uses the image background value, angular meteor speed and the lateral width of the meteor image to simulate the true and saturated light curve of meteors. For group I meteors, we computed a saturation correction and applied it to the saturated light curve. We then compared the corrected saturated curve to the unsaturated curve from the other camera to validate the model. For group II meteors, a saturation correction is calculated and applied to both observed light curves, which have different degrees of saturation, and the corrected curves are compared. We collected 516 meteors, of which 30 were of group I, and seven of group II. For meteors in group I, an average residual of less than 0.4 mag was found between the observed unsaturated light curve and the model-corrected saturated light curve. For meteors in group II, the average residual between the two corrected light curves was 0.3 mag. For our data, the saturation correction goes from 0.5 to 1.9 mag for meteors in group I, and 1.2 to 2.5 mag for meteors in group II. Based on the agreement between the observed and modelled light curves (less than 0.4 mag over all meteors of all groups), we conclude that our model for saturation correction is valid. It can be used to extract the true luminosity of a saturated meteor, which is necessary to calculate photometric mass. Our model also demonstrates that fixed corrections to saturated meteor photometry, not accounting for background levels or angular velocities, do introduce significant error to meteor photometric analyses.

Relationship between the summing-localization behavior and perceived width of sound image

We examined the relationship between the summing-localization behavior and perceived width of a sound image via two hearing experiments based on relative comparisons of the perceived directions to two sound stimuli. Two types of sound stimuli were employed. One stimulus, the “composite stimulus,” was generated by two sound sources located in horizontal plane with time lag (−3.0 to 3.0 ms) between them. The composite stimulus produced a perception of the summing localization or precedence effect. The other stimulus was generated by a single sound source as the reference for the perceived sound image. The first experiment (Exp. 1) investigated the relationship between the perceived direction of the composite stimulus and the time lag between the sound sources. The second experiment (Exp. 2) was carried out in order to compare the perceived width of the composite stimulus to that of the reference stimulus. The results of Exp. 1 demonstrated that the perceived direction of the composite stimulus smoothly shifted from the middle of the sound sources to that generating the preceding sound, these findings roughly corresponded to the results of the past studies. However, the tendency of the shift was different among the subjects, and could be classified into two types according to whether the shift reached the direction of the preceding source. The results of Exp. 2 showed that the “included range,” defined as the range for which the direction of the reference stimulus is perceived as included within the fused image of the composite stimulus, differed for each subject. The maximum width of the included range was over 30 degrees. From the results of Exps. 1 and 2 taken together, it is clear that there are individual differences with respect to how direction of a stimulus is perceived, within the included range of the fused sound image. This implies that the difference in the answer policy of each subject makes this difference.

Correcting distortion in a monochromatic imaging spectrometer for application to elemental imaging by glow discharge-optical emission spectrometry

A method to correct for instrumentally introduced image distortion in a monochromatic imaging spectrometer (MIS) was developed, evaluated and applied to surface elemental imaging in glow discharge-optical emission spectrometry. The method is based on fixed-spatial-frequency images, in which calibration points are localized to characterize the distortion at a given wavelength. In the MIS, a linear increase in image width with wavelength was found in the horizontal dimension, whereas no significant image distortion in the vertical dimension was observed. The ratio between the horizontal and vertical image widths was 18 ± 2% at 400 nm and 46 ± 2% at 750 nm. Correction of distorted images was performed computationally by means of bilinear interpolation. The geometric error, in terms of residuals of the interpolation, was calculated for every pixel in the reconstructed image (512 × 512 array) and typically found to be between 0.12 and 0.18 pixel. The developed method was applied to elemental imaging by glow discharge—optical emission spectrometry as a proof of principle. A glow discharge cell suitable for large-format elemental imaging (7.29 cm-diameter sputtering area) was used for imaging of circular brass samples. Significant differences between vertical and horizontal emission profiles from distorted emission maps (e.g. Zn I 481.05 nm: 30% difference between vertical and horizontal FWHM) could be successfully corrected (4.8% difference after correction) by the method presented here.