Distortion Map Research Articles

Robust three-dimensional face reconstruction by one-shot structured light line pattern

Three-dimensional face reconstruction is important in many intelligent human-machine applications, e.g. automatic face authentication, human computer interface based entertainment and robotic surgery. Most state-of-the-art structured light methods require multiple projections of the designed patterns, which is not desirable for face reconstruction because it is uncomfortable or difficult for a person to keep his/her face rigid for a period of time. In this paper, we propose an approach to reconstruct the three-dimensional face by one-shot of structured light line pattern. The proposed one-shot 3D reconstruction approach calculates the distortion map from the distorted structured light line pattern. It relies on robust image processing methods and the generic features of human face to segment and cluster the projected structured light line pattern from one single captured image. The y coordinates of the clustered lines are extracted to form a low-resolution distortion matrix which is then transformed to full-resolution distortion map by spline interpolation. The 3D face is reconstructed from the distortion map and the calibrated parameters. Experimental results show that the proposed approach is able to reconstruct the three-dimensional human face robustly by one-shot.

No-reference quality metric for HEVC compression distortion estimation in depth maps

Multiview video plus depth (MVD) is the most popular 3D video format due to its efficient compression and provision for novel view generation enabling the free-viewpoint applications. In addition to color images, MVD format provides depth maps which are exploited to generate intermediate virtual views using the depth image-based rendering (DIBR) techniques. Compression affects the quality of the depth maps which in turn may introduce various structural and textural distortions in the DIBR-synthesized images. Estimation of the compression-related distortion in depth maps is very important for a high-quality 3D experience. The task becomes challenging when the corresponding reference depth maps are unavailable, e.g., when evaluating the quality on the decoder side. In this paper, we present a no-reference quality assessment algorithm to estimate the distortion in the depth maps induced by compression. The proposed algorithm exploits the depth saliency and local statistical characteristics of the depth maps to predict the compression distortion. The proposed ‘depth distortion evaluator’ (DDE) is evaluated on depth videos from standard MVD database compressed with the state-of-the-art high-efficiency video coding at various quality levels. The results demonstrate that DDE can be used to effectively estimate the compression distortion in depth videos.

Geographically weighted bidimensional regression on the 17th-century map of a castle town in Japan

Abstract. Previous studies on historical maps have frequently used the bidimensional regression method to analyze the distortion of the maps. In many cases, however, the residuals of bidimensional regression are spatially auto-correlated. Of course, we can understand map distortions by those spatially auto-correlated residuals. At the same time, however, there is a possibility for another approach, which is to expand the bidimensional regression method to one consisting of spatial auto-correlations. Geographically weighted regression is a famous example of such a regression method that consists of spatial auto-correlations. Thus, a new method, called geographically weighted bidimensional regression, is proposed in this study. This regression method was applied to the 17th-century map of a castle town in Japan. The results indicate that spatial auto-correlation of residuals no longer exists. In addition, local parameters of the new method can describe map distortions directly. Ordinary bidimensional regression divides map distortions into global distortions and local distortions, which means that the ordinary technique assumed global distortions. The new method, however, can explore map distortions without assuming global distortions.

Sensorimotor maps can be dynamically calibrated using an adaptive-filter model of the cerebellum.

Substantial experimental evidence suggests the cerebellum is involved in calibrating sensorimotor maps. Consistent with this involvement is the well-known, but little understood, massive cerebellar projection to maps in the superior colliculus. Map calibration would be a significant new role for the cerebellum given the ubiquity of map representations in the brain, but how it could perform such a task is unclear. Here we investigated a dynamic method for map calibration, based on electrophysiological recordings from the superior colliculus, that used a standard adaptive-filter cerebellar model. The method proved effective for complex distortions of both unimodal and bimodal maps, and also for predictive map-based tracking of moving targets. These results provide the first computational evidence for a novel role for the cerebellum in dynamic sensorimotor map calibration, of potential importance for coordinate alignment during ongoing motor control, and for map calibration in future biomimetic systems. This computational evidence also provides testable experimental predictions concerning the role of the connections between cerebellum and superior colliculus in previously observed dynamic coordinate transformations.

Landscape evolution in the area of Kazimierski Landscape Park

Abstract The presented research concerning the landscape evolution of the area of the Kazimierski Landscape Park assumed the analysis of landscape changes that took place in the western part of the Nałęczów Plateau in eastern Poland as a result of increased anthropopressure. To achieve this goal, the diverse data was employed: archives of the “Archeological Survey of Poland” obtained from the National Heritage Board of Poland, the registry data from the 16th century made available as part of the “Atlas Fontium” project elaborated by the Institute of History of the Polish Academy of Sciences, old map of the Western Galicia from 1808, a tactical map of the Military Geographical Institute in Warsaw from 1937, and the “Topographic Objects Database” (BDOT10k) obtained from the Head Office of Geodesy and Cartography. Based on the analysed data, maps presenting the development of the settlement network from the moment of permanent settlement of the area up to the present state and maps showing the changes in land use in the Kazimierski Landscape Park over the last centuries have been designed. The results of historical and geographical analyses carried out as part of the research were compared with the results of geomorphological research conducted in the studied area. Verification of the obtained results allowed to determine the scope in which man influenced the evolution of the landscape of the analysed area, including its diversification depending on the historical period and the type of the economy. The process of georeferencing the map of Western Galicia elaborated by colonel A.M. von Heldensfeld from 1808 and the tactical map 1:100,000 of Military Geographical Institute from 1937 covering the research area (14,974 ha) was carried out in the ArcGIS Desktop software. The calibration process was evaluated in the Map Analyst program which makes it possible to analyze the distortions of old maps. Then, vectorization of selected terrain coverage classes and visualization of spatial data were conducted. This way, the land use maps were analyzed in terms of environmental changes that occurred over the past centuries by identifying the areas with the largest development changes. The obtained results were compared with the database of historical objects created for the purposes of this research, based on data provided by the National Heritage Board of Poland and the Institute of History of the Polish Academy of Sciences in order to determine the development trends of the settlement network in the region. The additional statistical analysis made it possible to determine the trend of changes and to interpret the distribution of areas threatened by the occurrence of mass movements with the analyzed anthropogenic determinants.

Domain Adaptation With Discriminative Distribution and Manifold Embedding for Hyperspectral Image Classification

Hyperspectral remote sensing image classification has drawn a great attention in recent years due to the development of remote sensing technology. To build a high confident classifier, the large number of labeled data is very important, e.g., the success of deep learning technique. Indeed, the acquisition of labeled data is usually very expensive, especially for the remote sensing images, which usually needs to survey outside. To address this problem, in this letter, we propose a domain adaptation method by learning the manifold embedding and matching the discriminative distribution in source domain with neural networks for hyperspectral image classification. Specifically, we use the discriminative information of source image to train the classifier for the source and target images. To make the classifier can work well on both domains, we minimize the distribution shift between the two domains in an embedding space with prior class distribution in the source domain. Meanwhile, to avoid the distortion mapping of the target domain in the embedding space, we try to keep the manifold relation of the samples in the embedding space. Then, we learn the embedding on source domain and target domain by minimizing the three criteria simultaneously based on a neural network. The experimental results on two hyperspectral remote sensing images have shown that our proposed method can outperform several baseline methods.

Occlusion-Aware Depth Map Coding Optimization Using Allowable Depth Map Distortions

In depth map coding, rate-distortion optimization for those pixels that will cause occlusion in view synthesis is a rather challenging task, since the synthesis distortion estimation is complicated by the warping competition and the occlusion order can be easily changed by the adopted optimization strategy. In this paper, an efficient depth map coding approach using allowable depth map distortions is proposed for occlusion-inducing pixels. First, we derive the range of allowable depth level change for both the zero disparity error case and non-zero disparity error case with theoretic and geometrical proofs. Then, we formulate the problem of optimally selecting the depth distortion within allowable depth distortion range with the objective to minimize the overall synthesis distortion involved in the occlusion. The unicity and occlusion order invariance properties of allowable depth distortion range is demonstrated. Finally, we propose a dynamic programming based algorithm to locate the optimal depth distortion for each pixel. Simulation results illustrate the performance improvement of the proposed algorithm over the other state-of-the-art depth map coding optimization schemes.

Constraints on non-resonant photon-axion conversion from the Planck satellite data

The non-resonant conversion of Cosmic Microwave Background (CMB) photons into scalar as well as light pseudoscalar particles such as axion-like particles (ALPs) in the presence of turbulent magnetic fields can cause a unique, spatially fluctuating spectral distortion in the CMB. We use the publicly available Planck temperature maps for the frequency channels (70–545 GHz) to obtain the first ALP distortion map using 45% clean part of the sky. The 95th percentile upper limit on the RMS fluctuation of ALP distortions from the cleanest part of the CMB sky at 15 arcmin angular resolution is 18.5 × 10−6. The RMS fluctuation in the distortion map is also consistent with different combinations of frequency channels and sky-fractions.

SurgeryCuts: Embedding Additional Information in Maps without Occluding Features

AbstractVisualizing contextual information to a map often comes at the expense of overplotting issues. Especially for use cases with relevant map features in the immediate vicinity of an information to add, occlusion of the relevant map context should be avoided. We present SurgeryCuts, a map manipulation technique for the creation of additional canvas area for contextual visualizations on maps. SurgeryCuts is occlusion‐free and does not shift, zoom or alter the map viewport. Instead, relevant parts of the map can be cut apart. The affected area is controlledly distorted using a parameterizable warping function fading out the map distortion depending on the distance to the cut. We define extended metrics for our approach and compare to related approaches. As well, we demonstrate the applicability of our approach at the example of tangible use cases and a comparative user study.

SIMBIO-SYS/STC stereo camera calibration: Geometrical distortion.

The STereo imaging Channel (STC) is the first push-frame stereo camera on board an European Space Agency (ESA) satellite, i.e., the ESA-Japan Aerospace eXploration Agency mission BepiColombo. It was launched in October 2018, and it will reach its target, Mercury, in 2025. The STC main aim is to provide the global three-dimensional reconstruction of the Mercury surface. STC, the stereo channel of spectrometer and imagers for Mercury Planetary Orbiter BepiColombo-Integrated Observatory System, is based on an original optical design that incorporates the advantages of a compact unique detector instrument and the convenience of a double direction acquisition system. In fact, STC operates in a push-frame imaging mode and its two optical sub-channels will converge the incoming light on a single focal plane assembly allowing to minimize mass and volume. The focal plane of the instrument is housing six different filters: two panchromatic filters in the range 600-800 nm and four broadband filters with central wavelengths in the range 420-920 nm. In this paper, the geometrical calibration of the instrument, including the optical setups used, will be described. The methods used to derive the focal lengths, the boresights, and the reference systems of the different filter models are presented, and the related distortion results are discussed. The STC off-axis configuration forced to develop a distortion map model based on the RFM (rational function model). In contrast to other existing models, which allow linear estimates, the RFM is not referred to specific lens geometry, but it is sufficiently general to model a variety of distortion types, as it will be demonstrated in this particular case.

Unveiling the nature of Gemini multiconjugate adaptive optics system distortions

Astrometry was not a science case of the Gemini Multiconjugate adaptive optics System (GeMS) at its design stage. However, since GeMS has been in regular science operation with the Gemini South Adaptive Optics Imager (GSAOI), their astrometric performances have been deeply analysed. The non-linear component of the distortion map model shows a characteristic pattern which is similarly repeated in each detector of GSAOI. The nature of this pattern was unknown and subjected to different hypotheses. This paper describes the origin of the GeMS distortion pattern as well as its multi-epoch variation. At the end, it is showed a comparison with the current design of the Multiconjugate Adaptive Optics RelaY (MAORY) of the Extremely Large Telescope (ELT).

Conformal initialization for shape analysis applications in SlicerSALT.

Shape analysis is an important method used in neuroimaging research community due to its potential to precisely locate morphological changes between healthy and pathological structures. A popular shape analysis framework in the neuroimaging community is based on the encoding surface locations as spherical harmonics for a representation called SPHARM-PDM.1 The SPHARM-PDM pipeline takes a set of brain segmentation of a single brain structure (for example, hippocampus) as input and converts them into a corresponding spherical harmonic description (SPHARM), which is then sampled into triangulated surface (SPHARM-PDM). At present, the SPHARM-PDM pipeline utilizes an area-preserving optimization of the spherical mapping based on an initial heat-equation based mapping of the surface mesh to the unit sphere. In the case of objects with complex shape, this initial spherical mapping suffers from a high degree of mapping distortion that cannot always be corrected by the following optimization procedure. Here we proposed the use of an alternative initialization based on a conformal flattening.2 This method adopts a bijective angle preserving conformal flattening scheme to replace the heat equation mapping scheme as initialization for use in the SPHARM-PDM pipeline. After quantitative measures of shape calculated from various complex structures, we concluded that in most cases, the new pipeline produced dramatically better results than the old pipeline. The main contribution of this paper is a command line tool based on the Slicer Execution Model, which merges the conformal flattening into the SPHARM-PDM pipeline for use in the SALT shape analysis toolbox.

Triangular mesh generation on free-form surfaces based on bubble dynamics simulation

Purpose Modern CAD systems facilitate the creation of any surface geometry imaginable, and complex surfaces for free-form grid shells are often represented by a set of Non-Uniform Rational B-Splines surface patches. But it remains an intractable issue how to generate high-quality grids on complex surfaces efficiently. To solve this issue, an automatic triangular mesh generation method is presented, based on bubble dynamics simulation and a modified Delaunay method. Design/methodology/approach A moderate amount of points are first distributed on a given surface. Next, by regarding the points as elastic bubbles with the same size and introducing the forces acting on bubbles, the motion control equations of bubbles are established. The equilibrium state of the bubble system is found by Verlet algorithm. Then, the Voronoi diagram on the surface is obtained by calculating the intersection between the surface and the three-dimensional (3D) Voronoi diagram of the centers of bubbles. Finally, a triangular mesh, Delaunay triangulation on the surface, is determined based on the dual change of the Voronoi diagram. Findings This method generates meshes on the surface directly, unlike mapping-based methods, avoiding the mapping distortion. Examples are given to demonstrate the successful execution of this method. The result also illustrates that this method is applicable to various surfaces in high automation level and resultant meshes are highly uniform and well-shaped. Originality/value Thus, this method provides the convenience for the geometry design of complex free-form grid structure.

Trochoidal toolpath for the pad-polishing of freeform surfaces with global control of material removal distribution

A trochoidal toolpath has an advantage in automated polishing owing to its multidirectional characteristic. Compared to most conventional toolpaths, a trochoidal toolpath has increased flexibility in its pattern control by involving more control parameters. In this work, the flexibility of a trochoidal toolpath has been applied in the pad-polishing of freeform surfaces using a tilted elastic disk, with global control of material removal distribution over part surfaces. Using the proposed approach, a novel mesh conformal parameterization-based algorithm is developed to simplify the complex trochoidal toolpath generation from freeform surfaces to a 2D domain, while considering mapping distortion. The material removal variation along the guide-line of the trochoidal toolpath is addressed by using optimized trochoidal step and radius, after precisely calculating the effect of overlapped toolpath trajectories. Moreover, adaptive feedrates for partitioned local regions are further proposed to address the material removal variation along the direction perpendicular to the trochoidal guide-line. Simulation and experimental studies are conducted and show that the fluctuation of removal depth can be considerably reduced with the global control of material removal distribution.

Generating Image Distortion Maps Using Convolutional Autoencoders With Application to No Reference Image Quality Assessment

We present two contributions in this work: 1) a reference-free image distortion map generating algorithm for spatially localizing distortions in a natural scene; and 2) no reference image quality assessment (NRIQA) algorithms derived from the generated distortion map. We use a convolutional autoencoder (CAE) for distortion map generation. We rely on distortion maps generated by the SSIM image quality assessment algorithm as the “ground truth” for training the CAE. We train the CAE on a synthetically generated dataset composed of pristine images and their distorted versions. Specifically, the dataset was created by applying standard distortions such as JPEG compression, JP2K compression, additive white Gaussian noise, and blur to the pristine images. SSIM maps are then generated on a per distorted image basis for each of the distorted images in the dataset and are in turn used for training the CAE. We first qualitatively demonstrate the robustness of the proposed distortion map generation algorithm over several images with both traditional and authentic distortions. We also demonstrate the distortion map's effectiveness quantitatively on both standard distortions and authentic distortions by deriving three different NRIQA algorithms. We show that these NRIQA algorithms deliver competitive performance over traditional databases like LIVE Phase II, CSIQ, TID 2013, LIVE MD, and MDID 2013, and databases with authentic distortions like LIVE Wild and KonIQ-10K. In summary, the proposed method generates high-quality distortion maps that are used to design robust NRIQA algorithms. Furthermore, the CAE-based distortion maps generation method can easily be modified to work with other ground truth distortion maps.

Approximation of metric spaces by Reeb graphs: Cycle rank of a Reeb graph, the co-rank of the fundamental group, and large components of level sets on Riemannian manifolds

For a connected locally path-connected topological space X and a continuous function f on it such that its Reeb graph Rf is a finite topological graph, we show that the cycle rank of Rf, i.e., the first Betti number b1(Rf), in computational geometry called number of loops, is bounded from above by the co-rank of the fundamental group ?1(X), the condition of local path-connectedness being important since generally b1(Rf) can even exceed b1(X). We give some practical methods for calculating the co-rank of ?1(X) and a closely related value, the isotropy index. We apply our bound to improve upper bounds on the distortion of the Reeb quotient map, and thus on the Gromov-Hausdorff approximation of the space by Reeb graphs, for the distance function on a compact geodesic space and for a simple Morse function on a closed Riemannian manifold. This distortion is bounded from below by what we call the Reeb width b(M) of a metric space M, which guarantees that any real-valued continuous function on M has large enough contour (connected component of a level set). We show that for a Riemannian manifold, b(M) is non-zero and give a lower bound on it in terms of characteristics of the manifold. In particular, we show that any real-valued continuous function on a closed Euclidean unit ball E of dimension at least two has a contour C with diam(C??E)??3.

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters.

To assure accurate treatment delivery on any image-guided radiotherapy system, the relative positions and walkout of the imaging and radiation isocenters must be periodically verified and kept within specified tolerances. In this work, we first validated the multiaxis ion chamber array as a tool for finding the radiation isocenter position of a magnetic resonance–guided linear accelerator. The treatment couch with the array on it was shifted in 0.2-mm increments and the reported beam center position was plotted against that shift and fitted to a straight line, in both X and Y directions. From the goodness-of-fit and intercepts of the regression lines, the accuracy and precision were conservatively estimated at 0.2 and 0.1 mm, respectively. This holds true whether the array is irradiated from the front or from the back, which allows efficient collecting the data from the 4 cardinal gantry angles with just 2 array positions. The average isocenter position agreed to within at most 0.4 mm along any cardinal axis with the linac vendor’s film-based procedure, and the maximum walkout radii were 0.32 mm and 0.53 mm, respectively. The magnetic resonance imaging isocenter walkout as a function of gantry angle was studied with 2 different phantoms, one employing a single fiducial at the center and another extracting the rigid displacement values from the distortion map fit of 523 fiducials dispersed over a large volume. The results were close between the 2 phantoms and demonstrated variation in the magnetic resonance imaging isocenter location as high as 1.3 mm along a single axis in the transverse plane. Verification of the magnetic resonance imaging isocenter location versus the gantry angle should be a part of quality assurance for magnetic resonance-guided linear accelerators.

A genetic system on chromosome arm 1BL of wild emmer causes distorted segregation in common wheat

Nonrandom segregation ratios of alleles 'segregation distortion' can have a striking impact on transmission genetics, and with widespread availability of genetic markers has been shown to be a frequent phenomenon. To investigate the possible effect of genetic interaction on segregation distortion and genetic map construction, the segregation and mapping of genetic markers locatedon wheat chromosomes 1A and 1B were followed in four recombinant substitution line (RSL) populations, produced using four chromosome-arm substitution lines (CASLs 1AS, 1AL, 1BS and 1BL) of wild emmer (Triticum turgidum var. dicoccoides, accession TTD140) in the background of the common wheat (T. aestivum) cultivar Bethlehem (BLH), each crossed to BLH itself. Using these four RSL populations, four genetic maps of chromosome 1 arms were constructed. A total of 22 genetic markers representing 19 loci were assigned to chromosome 1A, and 32 markers representing 30 loci were assigned to 1B. For chromosome 1B, two linkage maps were also constructed using RFLP data of an F2 population derived from the same cross combination as the RSLs. The RSL and F2 maps varied in genetic distances, but showed the same linear order of DNA markers. Segregation analysis revealed strong selection against BLH alleles on chromosome 1B, skewing the allelic frequency distribution in favour of TTD in both F2 and RSL populations at all marker loci. On the contrary, strong selection against TTD alleles on chromosome 1A was detected for some loci in the BLH × CASL1AL RSLs, and their distribution was significantly skewed to BLH. F2 populations always showed more segregation distortion than the corresponding RSLs. More markers near the region of chromosome 1B shared by both CASL1BS and 1BL (∼55 cM on chromosome 1B across the centromere) showed significantly distorted segregation in the BLH × CASL1BL population than in thecorresponding BLH × CASL1BS populations. Six markers located on chromosome 1A region shared by CASL1AS and 1AL showed significantly distorted segregation in 1AL-RSL, while no marker showed distorted segregation in 1AS-RSL. These results indicated that genetic factor(s) in the centromere region cause the distorted segregation of genetic markers on wheat chromosome 1B.

Mapping distortion correction in freeform mirror testing by computer-generated hologram.

Distortion can be introduced in null testing using computer-generated holograms for off-axis aspheres or freeforms with significant deviation. It leads to the failure of testing results to guide deterministic optical processing. In this paper, based on ray tracing and calibration marks applied to a mirror surface, a high-accuracy method is proposed to correct the distortion. The correction error is less than 1mm. Second and fourth mirrors of a reflective telescope prototype with an F number of 6.5 and field of view of 76° are polished. In the process, distortion is corrected, and the position misalignment error is as small as 0.783mm. For the sake of alignment, the two mirrors are fixed on a 790 mm×390 mm SiC substrate. The root-mean-square value of the mirror surface error is 0.0433λ (λ=0.6328 μm) after ion beam finishing.

Projector distortion residual compensation in fringe projection system

In fringe projection profilometry system, the lens distortion of the projector is usually represented with the distortion coefficients, but it will result in large residual. To compensate this residual, a projector distortion residual compensation method is proposed in this paper. After system calibration, the original distortion map is generated with the distortion coefficients and the original ideal pattern can be pre-distorted with the original distortion map. Then, with pinhole model and fringe projection technique, a residual distortion map is built based on per-pixel measurement. Finally, the original distortion map can be refined with the residual distortion map, and the lens distortion residual error can be compensated. Experimental results show considerable accuracy improvement in both the full-field error of projector and the final point cloud of system. In addition, the proposed compensation method can be implemented conveniently without any sophisticated ancillary equipment or complicated procedure.