Pair Of Contours Research Articles

Perceiving Perpendicular and Parallel Contours in the Frontoparallel Plane

The perception of a pair of contours in a retinal image cannot be understood simply by adding up the perceptions of the individual contours. We compared the perception of configurations of contours in three psychophysical experiments. The results of the experiments were analyzed so that the quantitative comparison of the perceived configurations was possible. Thresholds estimated were substantially lower from a perpendicular junction than from a single contour or from a non-perpendicular junction. The lowest thresholds were observed from a pair of parallel contours. The results suggest that the visual system is sensitive to perpendicular junctions and parallel contours in a retinal image.

Study on the near wake of a honeycomb disk

Flow around and/or through a honeycomb disk is a common problem encountered in aggregation, filtration and sedimentation processes. Mean flow, turbulent statistics and flow structures behind a solid and a honeycomb disk were experimentally studied by 2D PIV system. The results revealed that the mean flow structure behind a honeycomb disk was quite different from that of the solid disk wake. Due to the extra fluid through the small holes on the disk, the recirculation zone of honeycomb disk was much smaller both in length and in width. Meanwhile, the entrainment of the shear layer was significantly reduced and the length of the wake was increased. As the result, the honeycomb disk drastically decreased the velocity deficit, the rate of velocity recovery. The cross-stream distributions of Reynolds normal stresses exhibited symmetry while Reynolds shear stress showed asymmetry at x/d=1, 3, 5, respectively. Using proper orthogonal decomposition (POD), it was found that, for both solid and honeycomb disk, the instantaneous wake configuration at reflectional-symmetry-breaking (RSB) mode with hairpin vortices periodically shedding could be detected by the first two POD modes. The POD mode 3 consisted of two pairs of contours, showed well plane-symmetric large-scale vortices shedding from the mixing layers region (y=±0.5D). Due to different wake recovery rate and the interaction between the backflow and the shear layer, mode 4 structures in the both near wakes were obviously different.

SU‐C‐BRB‐04: Delineation Uncertainty Maps: Proof of Concept Study for Recurrent Gynaecological Cancers

Purpose:To create a novel infrastructure which allows clinicians to record their GTV delineation uncertainty; to generate delineation uncertainty maps from this data and compare them to clinical GTVs.Methods:A contouring concept was developed in which clinicians draw up to two GTV boundaries per CT slice corresponding to the inner and outermost possible boundaries the GTV may have.A new uncertainty contouring tool was implemented in our research treatment planning system (TPS, DynaPlan) to accommodate these contour pairs and the derivation of delineation probability maps. 3D probability maps were generated from the contour pairs based on the minimum Chebyshev distance, at each pixel within the contours, from each boundary. The probability associated with each pixel was defined as the ratio of its distance from the inner boundary to the sum of its distances from each boundary.These tools were used to create probability maps using contours produced by a clinician experienced in treating recurrent gynaecological cancers. The corresponding 50% probability volumes (GTVP50) were compared against the observers corresponding clinical GTV (GTVC) contour, created in accordance with local clinical protocols, using the Jaccard Index.Results:This approach was successfully implemented within the research TPS. Comparisons between GTVC and GTVP50 were made for 10 recurrences from 9 patients. GTVC was larger than GTVP50 (p<0.01), with mean±s.d. volumes of 69.6±55.4cm3 and 61.6±53.7cm3 respectively, and a corresponding Jaccard Index of 0.83±0.11.Conclusion:Individual clinician's delineation uncertainty can be recorded and a corresponding uncertainty map derived. This is a crucial step in improving the handling of delineation uncertainty and moving away from population based margins, using techniques such as probabilistic treatment planning. Contours produced for recurrent gynaecological GTVs show the clinical GTV to be consistently larger than volume corresponding to 50% probability. Future work is to investigate non‐linear methods for generating these probability maps.This report is independent research arising from an NIHR/HEE Healthcare Science Doctoral Research Fellowship, David Bernstein, HCS‐DRF‐2014‐05‐005, supported by National Institute for Health Research (NIHR). The views expressed in this publication are those of the author(s); not necessarily those of the NHS, NIHR, Health Education England or Department of Health.

Pitch Processing in Children with Williams Syndrome: Relationships between Music and Prosody Skills.

Williams syndrome (WS), a genetic neurodevelopmental disorder, has been taken as evidence that music and language constitute separate modules. This research focused on the linguistic component of prosody and aimed to assess whether relationships exist between the pitch processing mechanisms for music and prosody in WS. Children with WS and typically developing individuals were presented with a musical pitch and two prosody discrimination tasks. In the musical pitch discrimination task, participants were required to distinguish whether two musical tones were the same or different. The prosody discrimination tasks evaluated participants’ skills for discriminating pairs of prosodic contours based on pitch or pitch, loudness and length, jointly. In WS, musical pitch discrimination was significantly correlated with performance on the prosody task assessing the discrimination of prosodic contours based on pitch only. Furthermore, musical pitch discrimination skills predicted performance on the prosody task based on pitch, and this relationship was not better explained by chronological age, vocabulary or auditory memory. These results suggest that children with WS process pitch in music and prosody through shared mechanisms. We discuss the implications of these results for theories of cognitive modularity. The implications of these results for intervention programs for individuals with WS are also discussed.

Contributions of contour frequency, amplitude, and luminance to the watercolor effect estimated by conjoint measurement

The watercolor effect is a long-range, assimilative, filling-in phenomenon induced by a pair of distant, wavy contours of different chromaticities. Here, we measured joint influences of the contour frequency and amplitude and the luminance of the interior contour on the strength of the effect. Contour pairs, each enclosing a circular region, were presented with two of the dimensions varying independently across trials (luminance/frequency, luminance/amplitude, frequency/amplitude) in a conjoint measurement paradigm (Luce & Tukey, 1964). In each trial, observers judged which of the stimuli evoked the strongest fill-in color. Control stimuli were identical except that the contours were intertwined and generated little filling-in. Perceptual scales were estimated by a maximum likelihood method (Ho, Landy, & Maloney, 2008). An additive model accounted for the joint contributions of any pair of dimensions. As shown previously using difference scaling (Devinck & Knoblauch, 2012), the strength increases with luminance of the interior contour. The strength of the phenomenon was nearly independent of the amplitude of modulation of the contour but increased with its frequency up to an asymptotic level. On average, the strength of the effect was similar along a given dimension regardless of the other dimension with which it was paired, demonstrating consistency of the underlying estimated perceptual scales.

SU‐E‐J‐73: Effect of 4D‐CT Image Artifacts On the 3D Lung Registration Accuracy: A Parametric Study Using a GPU‐Accelerated Multi‐Resolution Multi‐Level Optical Flow

Purpose: To perform a parametric study of the effect of registration parameters on 4D‐CT image registration accuracy.Methods and Materials: A GPU based 4D‐CT image registration that registers the 4D lung anatomy using a multi‐level multi‐contrast optical flow was used for this study. A set of 14 4D‐CT datasets was employed for this study. The multi‐level lung anatomy was segmented into the surface contour, blood vessels and parenchyma regions using OsiriX. The registration started at the lowest resolution of a 3D volume. Within each resolution level, the volumes were registered using optical flow. The motion field was first computed for surface contour pairs in the lowest resolution. At this stage, all the voxels except those on the surface contour (the lowest level of anatomical representation) were not included. GPU based Thin‐Plate Splines was applied to the motion field so that voxels surrounding the surface contour had an initial displacement motion, which was closer to the actual value. The motion field was iteratively updated until the highest (original) resolution of the volume was processed. Results: The GPU implementation provided a speed‐up of >50x as compared to the CPU implementation. The registration accuracy varied non‐linearly with the kernel size. For both kernel size and smoothness factor, a non‐linear correlation was observed towards the registration accuracy with an optimal value being 5 cu.mm and 200, respectively. The accuracy improved with the number of resolution and contrast levels with 4 and 3, respectively, providing optimal registration accuracy. Finally, usage of the first 3 anatomical level representations provided the optimum registration accuracy as opposed to 4 or more levels. Conclusion: A parametric 4D image registration analyses showed its relationship to the registration accuracy to be non‐linear. A patient breathing and CT‐scanner specific study will quantitatively relate the registration errors on treatment planning and delivery.

Common-Gate Load-Pull With Q-Band Application

A new technique is proposed for the design of linear power amplifiers at millimeter-wave frequencies where load-pull of large transistor output cells is difficult. The technique transforms the load-pull data on a small, standard foundry transistor layout to a pair of common-gate contours for the intrinsic device; one source-gate and one drain-gate. These are recombined as an intrinsic drain-source contour for a larger and arbitrary transistor layout. A Q-band driver amplifier for the ETSI 42-GHz point-to-point radio band has been designed using the proposed technique. The fabricated MMIC consumes 1 W and has a gain of 21 dB, with OIP3 of 35 dBm, OIP5 of 28 dBm and P1 dB of 23 dBm. The PAE is approximately 19%. The OIP3 to P1 dB and OIP3 to dc power ratios are believed to be the best reported to date.

Method: automatic segmentation of mitochondria utilizing patch classification, contour pair classification, and automatically seeded level sets

BackgroundWhile progress has been made to develop automatic segmentation techniques for mitochondria, there remains a need for more accurate and robust techniques to delineate mitochondria in serial blockface scanning electron microscopic data. Previously developed texture based methods are limited for solving this problem because texture alone is often not sufficient to identify mitochondria. This paper presents a new three-step method, the Cytoseg process, for automated segmentation of mitochondria contained in 3D electron microscopic volumes generated through serial block face scanning electron microscopic imaging. The method consists of three steps. The first is a random forest patch classification step operating directly on 2D image patches. The second step consists of contour-pair classification. At the final step, we introduce a method to automatically seed a level set operation with output from previous steps.ResultsWe report accuracy of the Cytoseg process on three types of tissue and compare it to a previous method based on Radon-Like Features. At step 1, we show that the patch classifier identifies mitochondria texture but creates many false positive pixels. At step 2, our contour processing step produces contours and then filters them with a second classification step, helping to improve overall accuracy. We show that our final level set operation, which is automatically seeded with output from previous steps, helps to smooth the results. Overall, our results show that use of contour pair classification and level set operations improve segmentation accuracy beyond patch classification alone. We show that the Cytoseg process performs well compared to another modern technique based on Radon-Like Features.ConclusionsWe demonstrated that texture based methods for mitochondria segmentation can be enhanced with multiple steps that form an image processing pipeline. While we used a random-forest based patch classifier to recognize texture, it would be possible to replace this with other texture identifiers, and we plan to explore this in future work.

Grouping by Closure Influences Subjective Regularity and Implicit Preference

A reflection between a pair of contours is more rapidly detected than a translation, but this effect is stronger when the contours are closed to form a single object compared to when they are closed to form 2 objects with a gap between them. That is, grouping changes the relative salience of different regularities. We tested whether this manipulation would also change preference for reflection or translation. We measured preference for these patterns using the Implicit Association Test (IAT). On some trials, participants saw words that were either positive or negative and had to classify them as quickly as possible. On interleaved trials, they saw reflection or translation patterns and again had to classify them. Participants were faster when 1 button was used for reflection and positive words and another button was used for translation and negative words, compared to when the reverse response mapping was used (translation and positive vs. reflection and negative). This reaction time difference indicates an implicit preference for reflection over translation. However, the size of the implicit preference was significantly reduced in the Two-objects condition. We concluded that factors that affect perceptual sensitivity also systematically affect implicit preference formation.

A new adaptive slicing approach for the fully dense freeform fabrication (FDFF) process

Fully dense freeform fabrication (FDFF) is a process based on thin line cutting processes, variable thickness layering, slicing in different orientations, and bulk layer attachment. The combination of these capabilities enables the production of good quality complex parts from practically any material at a very fast pace. As for rapid prototypes fabricated by the FDFF process, it is certainly possible to employ adaptive slicing technique due to the possibility of cutting different metal/non-metal sheet at various thicknesses. This paper proposes a new adaptive slicing method whereby the capability of cutting a 3D solid model at the predefined sheets' thicknesses is achieved and the geometry of all internal and external features of a part is also investigated to ensure the reduction of part geometry deviation through the seamless curvature detection. Despite most previous works which start slicing a tessellated or direct CAD model at the maximum available thickness, this system commences the process with available minimum thickness by applying a new adaptive method to all pairs of contours at the top and bottom slices of the layer. Autodesk Inventor solid modeler, as a design-by-feature solid modeler, is used for 3D solid modeling. The proposed system is implemented by Visual Basic codes inside Inventor using API functions to access both geometry and topology information of the design-by-feature solid model. This system has been successfully tested on a variety of complex parts containing sophisticated internal and external features.

On contour crossings in contour-advective simulations – part 1 – algorithm for detection and quantification

This is the first of two papers devoted to the analysis of contour crossing errors that occur in contour-advective simulations of fluid motion. Here an algorithm is presented for quantifying the error due to contour crossings. The first step is to determine the relative proximity of all possible pairs of contours. A digital representation of each contour is produced to aid in the corresponding calculation. Simple analysis of functions is then used to find any crossings between contours deemed close to each other by the digital representation method. Next, the area in error of a pair of crossing contours is calculated by identifying the polygon or polygons that approximately bound the erroneous region. Finally, some preliminary results of analysis of contour crossings that occur in contour-advective semi-lagrangian (CASL) simulations of single layer quasigeostrophic turbulence are presented. It is shown that the error due to contour crossings is small in the simulations considered here.

SU‐E‐J‐100: A Contour‐Guided Deformable Image Registration Algorithm for Adaptive Radiotherapy

Purpose: To develop a contour‐guided deformable image registration algorithm to improve the accuracy of deformation image registration in adaptive radiotherapy, especially for improving the accuracy of low contrast structures deformation. Methods: We developed an efficient algorithm to accurately deform low‐contrast structures in CT images. The new DIR algorithm is based on our original developed Demons algorithm by adding constraints defined by physician drawn contour pairs on images. By iteratively increasing the intensity of ROI enclosed by contour pairs, the optimization problem defined in Demons is ensured to converge to a desirable solution. Results: The new algorithm was validated on both a numerical phantom experiment and a clinical patient case. For the digital phantom experiment, a moving image is defined as two intersected spheres embedded in a cube and the contrast between spheres and cube is low; and a target image is a low‐contrast sphere in a cubic. For the clinical case, two CT images scanned for a head and neck cancer patient in one month apart are treated as a pair of moving and target images. The left parotids with anatomical changes are defined as structures of interest (SOIs). Qualitatively, with visual inspection, the proposed algorithm yields satisfactory results in both numerical and clinical testing cases. Quantitatively, root mean squares error (RMS) and normalized correlation coefficient (NCC) were calculated between the deformed and target SOI. Compared to the original Demons algorithm, the contour‐guided Demons algorithm results the decrease of RMS and the increase of NCC for both cases. Conclusions: The proposed contour‐guided demons algorithm permits us to take advantage of the structures defined by physicians to obtain more accurate image deformations. It provides a useful clinical tool for future interactive adaptive radiotherapy.

Polynomial Modeling of Child and Adult Intonation in German Spontaneous Speech

In a data set of 291 spontaneous utterances from German 5-year-olds, 7-year-olds and adults, nuclear pitch contours were labeled manually using the GToBI annotation system.Ten different contour types were identified.The fundamental frequency (F0) of these contours was modeled using third-order orthogonal polynomials, following an approach similar to the one Grabe, Kochanski, and Coleman (2007) used for English. Statistical analyses showed that all but one contour pair differed significantly from each other in at least one of the four coefficients.This demonstrates that polynomial modeling can provide quantitative empirical support for phonological labels in unscripted speech, and for languages other than English. Furthermore, polynomial expressions can be used to derive the alignment of tonal targets relative to the syllable structure, making polynomial modeling more accessible to the phonological research community. Finally, within-contour comparisons of the three age groups showed that for children, the magnitude of the higher coefficients is lower, suggesting that they are not yet able to modulate their pitch as fast as adults.

Affine invariant matching of broken boundaries in noisy images based on the quality migrant injection genetic algorithm and a successive erosion and distance accumulation scheme

Viewpoint invariant identification of fragmented scene contours can be realized by matching them against a collection of known reference models. For near planar objects, the matching of a pair of contours can be encapsulated as the search for the existence of an affine transform between them. Past research has demonstrated that the search process can be effectively accomplished with the integration of a simple genetic algorithm (SGA) and quality migrant injection (QMI), a method referred to as the quality migrant genetic algorithm (QMGA). Despite the favorable outcome, this method is extremely vulnerable to noise contamination on the image scene. In this paper we provide an explanation on the causes of this problem, and propose a solution known as successive erosion and distance accumulation (SEDA). Experimental evaluation shows that by supplementing the QMGA method with the proposed scheme, higher success rates can be attained in identifying matched contours under moderate amount of noise contamination.

Affine invariant matching of broken boundaries based on simple genetic algorithm and contour reconstruction

Viewpoint independent identification of fragmented object contours can be accomplished by matching them against a collection of known reference models. For the class of near-planar objects, the matching process can be posed as the search for the existence of an affine transform between a pair of contours. Recently, it has been demonstrated that the search process can be accomplished with the integration of a simple genetic algorithm (SGA) and a quality migrant injection (QMI) operation. The performance is superior to prior arts based on the use of SGA alone in terms of success rates and computation speed. The downside of such approach is the need of more computation time for generating quality migrants in the course of evolution. In this paper, we have proposed a solution to overcome this problem. Our method has two major contributions. The first one is a scheme which enables a closed boundary to be extracted from a set of fragmented object points, and represented as a one-dimensional ( 1 − D) sequence. Second, we have applied SGA to determine the similarity between a pair of closed boundaries by searching the existence of three correspondence point pairs in their 1 − D sequences. As a result of these two contributions, the proposed method is substantially faster than the SGA–QMI scheme, and also capable of attaining close to 100% success rate in identifying matched contours.

Sensitivity to Reflection and Translation is Modulated by Objectness

The salience of a transformation between a pair of contours depends on the type of transformation (eg a reflection or a translation) and also on figure-ground organisation. Reflection is most salient when both contours belong to the same surface, and translation is most salient when they do not connect a surface. These findings are based on reaction time (RT). Here I replicate and extend them by measuring both RT and sensitivity. The figure-ground relations were changed unambiguously by using stereograms. I compared reflection and translation when they were present within a surface or across surfaces (experiment 1), and within an object or a hole (experiments 2-4). Holes are interesting because they are not objects, but their presence does not increase the number of total objects in the scene. The within-surface advantage for reflection was present in all experiments. There was a between-surface advantage for translation in experiment 1 but there was no hole advantage for translation in experiments 2-4. Thus the effect of context, ie objectness, on detection of regularity is a robust and general phenomenon present in every experiment, but the type of interaction differs for reflection and translation.

An Active Contour Model for Segmenting and Measuring Retinal Vessels

This paper presents an algorithm for segmenting and measuring retinal vessels, by growing a "Ribbon of Twins" active contour model, which uses two pairs of contours to capture each vessel edge, while maintaining width consistency. The algorithm is initialized using a generalized morphological order filter to identify approximate vessels centerlines. Once the vessel segments are identified the network topology is determined using an implicit neural cost function to resolve junction configurations. The algorithm is robust, and can accurately locate vessel edges under difficult conditions, including noisy blurred edges, closely parallel vessels, light reflex phenomena, and very fine vessels. It yields precise vessel width measurements, with subpixel average width errors. We compare the algorithm with several benchmarks from the literature, demonstrating higher segmentation sensitivity and more accurate width measurement.

Affine invariant object shape matching using genetic algorithm with multi-parent orthogonal recombination and migrant principle

Genetic algorithm has served as a viable means for object shape matching. However, the success rate of correctly matching a pair of contours is generally low and inconsistent. In this paper a novel scheme based on the integration of two techniques: the migrant principle and multi-parent orthogonal recombination, are introduced to alleviate the problem. The proposed algorithm has been evaluated with object contours that are captured under good lighting condition, as well as images that have been contaminated with noise. In both cases experimental results revealed that the proposed method exhibited superior performance over its peers in terms of stability, speed, and success rate.

Biases and Sensitivities in the Poggendorff Effect when Driven by Subjective Contours

A consensus in the existing literature suggests that the Poggendorff effect (a perceptual misalignment of two collinear transversal segments when separated by a pair of parallel contours) persists when the parallels are defined by Kanizsa-like subjective contours. However, previous studies have often been complicated by a lack of quantitative measures of effect size, statistical tests of significance, appropriate measures of baseline and control biases, or stringent definition of subjective contours. The aim of this study was thus to determine whether subjective contours are capable of driving the Poggendorff effect once other factors are accounted for. Twenty participants were tested on a number of test and control figures incorporating first-order (luminance-defined) and subjective parallels using the method of adjustment. All figures were tested at two different orientations, and observer sensitivities and observer biases were assessed. A systematic response bias (in the direction of the classical effect) was found for Poggendorff figures that incorporated subjective parallels. The effect was highly significant and greater than for control figures. There was no concomitant change in judgment sensitivity (positional certainty). Finally, there was a positive correlation between the effect size for figures incorporating first-order and subjective parallels. The findings reported demonstrate conclusively that true Kanizsa-like subjective contours are capable of driving the Poggendorff effect. Further, the data are consistent with a growing body of evidence that suggests both first-order and subjective contours are processed at early loci in the visual pathways when position is encoded.

Integration of multi-modality imaging for accurate 3D reconstruction of human coronary arteries in vivo

In conventional intravascular ultrasound (IVUS)-based three-dimensional (3D) reconstruction of human coronary arteries, IVUS images are arranged linearly generating a straight vessel volume. However, with this approach real vessel curvature is neglected. To overcome this limitation an imaging method was developed based on integration of IVUS and biplane coronary angiography (BCA). In 17 coronary arteries from nine patients, IVUS and BCA were performed. From each angiographic projection, a single end-diastolic frame was selected and in each frame the IVUS catheter was interactively detected for the extraction of 3D catheter path. Ultrasound data was obtained with a sheath-based catheter and recorded on S-VHS videotape. S-VHS data was digitized and lumen and media-adventitia contours were semi-automatically detected in end-diastolic IVUS images. Each pair of contours was aligned perpendicularly to the catheter path and rotated in space by implementing an algorithm based on Frenet–Serret rules. Lumen and media-adventitia contours were interpolated through generation of intermediate contours creating a real 3D lumen and vessel volume, respectively. The absolute orientation of the reconstructed lumen was determined by back-projecting it onto both angiographic planes and comparing the projected lumen with the actual angiographic lumen. In conclusion, our method is capable of performing rapid and accurate 3D reconstruction of human coronary arteries in vivo. This technique can be utilized for reliable plaque morphometric, geometrical and hemodynamic analyses.