Stereo Research Articles

Prototype of Photometric Stereo System Using 6 and 9 LED Light Source to Reconstruct Human Skin Texture

A quantification of skin surface is one of challenging problem which is required in skin health assessment and efficacy evaluation of cosmetic products. Due to limitations of direct visual assessment of skin microscopic topography, an optical dermastocopy is commonly used as skin imaging device to magnify skin topography based on a white light reflection. The limitation of this method is its poor spatial resolution to quantify skin topography. In this paper, a skin imaging based on photometric stereo is proposed to visualize microscopic topography of human skin. The prototype was developed based on modification of illumination source system on the digital microscope. The illumination system consists of 6 and 9 super-bright LED. Additional electronic circuit was integrated with illumination system in order to control LED so that it can light successively. After that, set of images acquired in different angle of illumination was recorded. All images will be reconstructed using software to obtain stereo images, which shows the depth of the surface. Implementation on skin surface profile performed on three test areas: the back of the hand and knuckle creases. Based on qualitative analysis, our proposed scheme of skin imaging based on photometric stereo is promising for surface profile measurement and imaging of the skin.

Trinocular stereo system with object space oriented correlation for inner pipe inspection

Geometric inspection of pipes is a fundamental task in the oil industry. This work shows the development of a system to measure the geometry of a pipe’s inner wall using a trinocular stereo system. Natural pipe texture is used to produce a point cloud intrinsically organized in a regular mesh in a cylindrical coordinate system. The main novelty in the proposed algorithm is the definition of a regular kernel in object space, which is mathematically projected to each image plane using the inverse triangulation approach. The use of a triple correlation coefficient estimator led to simultaneous detection of homologous points. Experiments depict measurements of pipes with real and simulated textures, and results on a calibrated pipe of approximately 150mm in diameter showed a mean error of 0.3mm with a standard deviation of 0.2mm.

Optimized projection patterns for stereo systems

This paper describes how to generate optimal projection patterns to supplement general stereo camera systems. In contrast to structured light, the active stereo systems utilize the projected patterns only as auxiliary information in correspondence search, whereas the structured light systems have to detect the patterns and decode them to compute depth. The concept of non-recurring De Bruijn sequences is introduced, and a few algorithms based on the non-recurring De Bruijn sequence are designed to build optimized projection patterns for several stereo parameters. When only the search window size of a stereo system is given, we show that a non-recurring De Bruijn sequence with corresponding parameters makes the longest functional pattern, and presents experimental results using real scenes to show the effectiveness of the proposed projection patterns. Additionally if the pattern length is given in the form of maximum disparity search range, the algorithm using branch-and-bound search scheme to find an optimal sub-sequence of a non-recurring De Bruijn sequence is proposed.

LOD Generation for Urban Scenes

We introduce a novel approach that reconstructs 3D urban scenes in the form of levels of detail (LODs). Starting from raw datasets such as surface meshes generated by multiview stereo systems, our algorithm proceeds in three main steps: classification, abstraction, and reconstruction. From geometric attributes and a set of semantic rules combined with a Markov random field, we classify the scene into four meaningful classes. The abstraction step detects and regularizes planar structures on buildings, fits icons on trees, roofs, and facades, and performs filtering and simplification for LOD generation. The abstracted data are then provided as input to the reconstruction step which generates watertight buildings through a min-cut formulation on a set of 3D arrangements. Our experiments on complex buildings and large-scale urban scenes show that our approach generates meaningful LODs while being robust and scalable. By combining semantic segmentation and abstraction, it also outperforms general mesh approximation approaches at preserving urban structures.

Occupancy-elevation grid: an alternative approach for robotic mapping and navigation

SUMMARYThis paper proposes an alternative environment mapping method for accurate robotic navigation based on 3D information. Typical techniques for 3D mapping using occupancy grid require intensive computational workloads in order to both build and store the map. This work introduces an Occupancy-Elevation Grid (OEG) mapping technique, which is a discrete mapping approach where each cell represents the occupancy probability, the height of the terrain and its variance. This representation allows a mobile robot to know with an accurate degree of certainty whether a place in the environment is occupied by an obstacle and the height of such obstacle. Thus, based on its hardware characteristics, it can make calculations to decide if it is possible to traverse that specific place. In general, the map representation introduced can be used in conjunction with any kind of distance sensor. In this work, we use laser range data and stereo system data with a probabilistic treatment. The resulting maps allow the execution of tasks as decision making for autonomous navigation, exploration, localization and path planning, considering the existence and the height of the obstacles. Experiments carried out with real data demonstrate that the proposed approach yields useful maps for autonomous navigation.

David Yue (1957-2014).

Dr David Yue died suddenly and tragically in his laboratory on 23 December 2014. We write as his friends and colleagues to express our deepest sympathy to his family, while acknowledging his stellar accomplishments as a scientist, teacher, mentor and programme leader. Dr Yue studied for his undergraduate degree in Biochemistry at Harvard College and then earned an MD and PhD from Johns Hopkins University. As a Faculty member in Bioengineering and Neurosciences at Johns Hopkins University, Dr Yue earned an international reputation as one of the world's most innovative and accomplished cellular and molecular physiologists/biophysicists/bioengineers. The consistent and very important goal of his work was to obtain an understanding of the molecular details of key aspects of Ca2+ fluxes and [Ca2+]i homeostasis in mammalian cells, and thus discover fundamental physiological mechanisms. Some of his early work was done on cardiac muscle, using a combination of experimental protocols and bioengineering approaches to measure [Ca2+]i and force production. This work resulted in an improved and novel understanding of the relationship between [Ca2+]i and active force generation that governs the mechanical properties of the mammalian ventricle. Later, Dr Yue's major scientific focus was on the molecular physiology, biophysics and pharmacology of selected Ca2+ channels, with an emphasis on molecular mechanisms and their modulation by calmodulin. An excellent series of papers over a 15 year period collectively stand out as being one of the most innovative, creative and rigorous bodies of work done by any cell physiology laboratory worldwide. This was recognized when Dr. Yue received the prestigious Kenneth Cole Award from the Biophysical Society in 2011. The Yue laboratory was the first to draw attention to the fact that the C-terminal segment of the L-type Ca2+ channel can itself significantly modulate Ca2+ channel function. In addition, a clever and complex combination and application of electrophysiological principles, optical techniques and applied mathematics allowed the Yue group significantly to advance the understanding of the functional role of calmodulin in mammalian cells. In these studies, Dr Yue and his trainees identified and then demonstrated key aspects of Ca2+ signalling in mechanistic detail. They found that there are two very different functional roles for two molecular domains on the calmodulin molecule. One module senses Ca2+ and regulates downstream signalling using a signal transmission mode that, by analogy to a stereo system, would be considered frequency modulated. In contrast, a second lobe of the same molecule operates mainly as an amplitude sensor. In combination, these two calmodulin-based signals explain essential aspects of short-term and long-term regulation by Ca2+ of fundamental neurophysiological processes, such as long-term potentiation and depression, and transcriptional regulation. In addition to these remarkable, in fact unique, scientific contributions, Dr David Yue was well known and much respected as a mentor of graduate students and postdoctoral fellows and as a commi-tted and exceptionally effective teacher. Both his students and his Faculty colleagues rank his commitment to and effectiveness in teaching, mentoring and programme development as being equal to his very impressive scientific record. Many of the papers in this supplemental issue of The Journal of Physiology are based on or relate importantly to fundamental mechanisms for regulation of intracellular Na+ and Ca2+ in the mammalian heart. These physiological principles and resulting pathophysiological sequelae, e.g. ventricular arrhythmias, relate closely to some of the most recent work from the Yue laboratory (Ben-Johny et al. 2014; Ben-Johny & Yue, 2014). Indeed, David Yue and his colleagues were very well positioned to make further significant advances concerning Ca2+- and calmodulin-mediated mechanisms of cardiac arrhythmias (Limpitikul et al. 2014; Park et al. 2014). David Yue was an exceptional scientist and academic leader. The untimely interruption of his extremely productive and impactful career leaves a very significant void in fields such as cellular and molecular physiology. We recognize, however, that the most tragic aspect of the passing of David Yue is the loss of this committed father, husband and mentor.

Refocusing images and videos with a conventional compact camera

Digital refocusing is an interesting and useful tool for generating dynamic depth-of-field (DOF) effects in many types of photography such as portraits and creative photography. Since most existing digital refocusing methods rely on four-dimensional light field captured by special precisely manufactured devices or a sequence of images captured by a single camera, existing systems are either expensive for wide practical use or incapable of handling dynamic scenes. We present a low-cost approach for refocusing high-resolution (up to 8 mega pixels) images and videos based on a single shot using an easy to build camera-mirror stereo system. Our proposed method consists of four main steps, namely system calibration, image rectification, disparity estimation, and refocusing rendering. The effectiveness of our proposed method has been evaluated extensively using both static and dynamic scenes with various depth ranges. Promising experimental results demonstrate that our method is able to simulate various controllable realistic DOF effects. To the best of our knowledge, our method is the first that allows one to refocus high-resolution images and videos of dynamic scenes captured by a conventional compact camera.

The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent a series of upgrades, involving the exchange of the MAGIC-I camera and its trigger system, as well as the upgrade of the readout system of both telescopes. We use observations of the Crab Nebula taken at low and medium zenith angles to assess the key performance parameters of the MAGIC stereo system. For low zenith angle observations, the standard trigger threshold of the MAGIC telescopes is ∼ 50GeV. The integral sensitivity for point-like sources with Crab Nebula-like spectrum above 220GeV is (0.66 ± 0.03)% of Crab Nebula flux in 50h of observations. The angular resolution, defined as the σ of a 2-dimensional Gaussian distribution, at those energies is ≲ 0.07°, while the energy resolution is 16%. We also re-evaluate the effect of the systematic uncertainty on the data taken with the MAGIC telescopes after the upgrade. We estimate that the systematic uncertainties can be divided in the following components: < 15% in energy scale, 11%–18% in flux normalization and ± 0.15 for the energy spectrum power-law slope.

Real-time line matching from stereo images using a nonparametric transform of spatial relations and texture information

We propose a real-time line matching method for stereo systems. To achieve real-time performance while retaining a high level of matching precision, we first propose a nonparametric transform to represent the spatial relations between neighboring lines and nearby textures as a binary stream. Since the length of a line can vary across images, the matching costs between lines are computed within an overlap area (OA) based on the binary stream. The OA is determined for each line pair by employing the properties of a rectified image pair. Finally, the line correspondence is determined using a winner-takes-all method with a left-right consistency check. To reduce the computational time requirements further, we filter out unreliable matching candidates in advance based on their rectification properties. The performance of the proposed method was compared with state-of-the-art methods in terms of the computational time, matching precision, and recall. The proposed method required 47 ms to match lines from an image pair in the KITTI dataset with an average precision of 95%. We also verified the proposed method under image blur, illumination variation, and viewpoint changes.

Italian seas wave extremes: a preliminary assessment

Occasional damages occurring to offshore structures and routing ships have brought attention on whether conventional analyses of stormy seas are adequate to represent wave extremes. Indeed, field and laboratory data showed that in short-crested seas (typical of stormy conditions) the maximum wave elevation is rarely retrieved by a single-point observation (a buoy, for example), which tends to underestimate the actual extreme that occurs over an area surrounding the point. Recently, stochastic models for the prediction of maxima of multidimensional Gaussian random fields (e.g. the Piterbarg’s theorem and the Adler and Taylor’s Euler Characteristics approach) have been successfully applied to ocean wave statistics, thus permitting to extend the extreme value analysis from the time to the space–time domain. Results from space–time models are here firstly compared to observations gathered by an optical stereo system, and then used to preliminarily assess wave extremes over the Italian Seas, by using a numerical model analysis covering the period 2007–2013. In particular, space–time maxima are estimated as affecting a fishing boat and a cruise ship, showing that, locally, space–time extremes may exceed time-based values up to about 50 %.

English

Stereoscopy is a technique used for recording and representing stereoscopic (3D) images. It can create an illusion of depth using two pictures taken at two or more slightly different positions. There are two possible way of taking stereoscopic pictures by using special two-lens stereo cameras or systems with two single-lens cameras joined together. Stereoscopic pictures allow us to calculate the distance from the camera(s) to the chosen object within the picture. One of the most important features for any intelligent ground vehicle is based on how is reliable and complete the perception of the environment and the capability to discriminate what an obstacle is. Stereovision system used to detect the distance from the obstacle by disparity of images. Stereo vision system provides pair of stereo images to determine distance after the detecting the object and measure distance from it and avoid the object. Avoidance done by any of the controlling device when getting the detection decision form stereo system.

Stochastic Optimization Based 3D Dense Reconstruction from Multiple Views with High Accuracy and Completeness

This paper presents a stochastic optimization based 3D dense reconstruction from multiple views. Accuracy and completeness are two major measure indices for performance evaluation of various multi-view stereo (MVS) algorithms. First, the reconstruction accuracy is highly related to the stereo mismatches over the multiple views. Stereo mismatches occur in the image regions involving the lack of texture, depth discontinuity, or repeated texture patterns. Second, an insufficient number of views or occlusions between objects also lead to the difficulty in matching so that the reconstruction completeness degrades. In pursuit of high accuracy and completeness we present the appropriate techniques to solve the above problems in the reconstruction task. To deal with the various stereo mismatch problems we propose to apply adaptive matching functions and allow partial matching. We shall model the object to be reconstructed by a set of 3D oriented planar patches covering the visible object surface. The adopted multi-view reconstruction is formulated as a patch expansion process under a tree hierarchy. In order to find the optimal patches via multi-view stereo matching we shall employ a PSO (Particle Swarm Optimization) method for the sake of implementation simplicity and avoidance of possible local traps as found in the derivative based optimization methods. The success in the PSO method relies on imposing proper constraints on ranges of the patch parameters including the patch depth and patch normal vector which are involved in the PSO objective function (i.e., the stereo matching function). Furthermore, we use a varying patch size to obtain the reliable patches in the areas containing less texture, repeated texture pattern, or depth discontinuity. To secure a high reconstruction quality we advocate a patch priority queue to select the best patch during the patch expansion. All of the above mentioned techniques are also effective in the situations when the number of views is sparse or the camera baseline width is wide. The proposed method is tested on synthetic and real image data sets. The experimental results indicate that the proposed method is superior or comparable to the top ranked reconstruction methods reported in the public Middlebury MVS evaluation website.

Detection of hidden vertical root fracture by stereomicroscope

The vertical root fractures resulting as from trauma, as from the “cracked tooth syndrome”, are spotted within the “iatrogenic periodontal lesions” according to the Al-Fouzan (1) classification. The stereo microscope, an optical microscope variant typically exploiting the light reflected from the surface of an object rather than that transmitted through it (2), in the reported case has revealed the best tool to perform the resolving three-dimensional examination of the tooth. Aim of this paper is to describe a vertical root fracture, not otherwise detectable. A second upper molar, has been endodontically treated, because of the presence of an endo-periodontal lesion. Even though the treatment was performed according the standard protocol, after two years the lesion persisted and the tooth was extracted. After the extraction, the tooth was diaphanized to be observed with the stereomicroscope (Leica LED2000). The investigation clearly showed a vertical fracture, starting directly from the cervical line and a small hole on the distal surface of the root palatal cone. Mean values of measurements taken in 15 randomly points at 1x, 4x and 8x magnification were made. The fracture resulted to be long 9,79 mm and to have a mean width of 0,37 + 0,07 mm externally, and 0,15 + 0,02 mm internally. The mean area of the hole resulted of 0,85 mm2. All the analytical procedure was validated by t-student test, showing a p value < 0,0001. This vertical root fracture represented the unexpected pathway between the pulp and periodontal tissues and sure it caused the endodontic treatment failure, with tooth loss. It appears clear that a good diagnosis, following exactly the proto- col stated in the literature, together with the patient’s compliance, are crucial basis to face such clinical challenge.

Retrieving cloud top height in the JEM-EUSO cosmic-ray observation system

The main telescope of JEM-EUSO will determine Ultra High Energy Cosmic Ray properties by measuring the UV fluorescence light generated in the interaction between the cosmic rays and the atmosphere. Therefore, cloud information is crucial for a proper interpretation of the data. JEM-EUSO will observe the clouds in the field of view of the telescope making use of an atmospheric monitoring system, which consists of a LIDAR and an IR Camera. To retrieve the cloud top height from IR images two different methodologies will be used. The first one is based on stereo vision algorithms and requires two different views of the same scene. The second one is based on the relationship between the cloud top temperature and the cloud top height. From the IR camera the brightness temperature can be retrieved, thus the developed Split Window Algorithm retrieves the real cloud temperature from the brightness temperature in two spectral bands. This article presents a preliminary work, in which both methodologies are compared with the height given by MODIS. The stereo system is provided by the two geostationary satellites MSG-2 and MSG-3. The Split Window Algorithm has been tested in MODIS images of bands 31 and 32. This initial work is a first step to compare a very simplified version of both methodologies.

Subjective Comparison Experiments of DMS and Conventional Stereo

Multi-channel dynamic matrix sound system (DMS) is a multi-channel input and output sound system which is based on source synthesis and Huygens' principle. The sound sources are recorded by microphone array and multi-channel independent recording, instead of the field. This paper describes the results of the subjective evaluation experiments between DMS and conventional stereo system by the semantic differential (SD) method. Five parts of the audio materials and a training material, including the human voice, music, sound effects, were used as the stimuli. All of the stimuli were recorded by the DMS and conventional stereo system respectively. The results proof that the effectiveness of DMS, which has a higher level of sound quality and can give the audience the experience of dynamic subjective feelings compared with conventional stereo system. Furthermore, sound designers must carefully consider the influence of gender, age, preferences on the hearing impression.

Effect of dentin proteoglycans on the bonding properties of dentin

To investigate the potential effect of proteoglycan (PG) and glycosaminoglycan (GAG) on the bonding of etch and rinse adhesive to dentin, in order to improve the bonding effect of dentin. Forty-two extracted molars were used to obtain standard dentin bonding surface, and the specimens were etched for 15 s with 37% phosphoric acid and divided into three groups using a table of random numbers. Then the three groups undergone different incubating procedures as follow: specimens in chondroitinase ABC (C-ABC) group were incubated with C-ABC at 37 °C for 48 h in vibrator. Specimens in trypsin (TRY) group were incubated with trypsin, and specimens in the control group were incubated with deionized water for 48 h in the oscillators. Then specimens in each group were randomly assigned into two subgroups, A (Adper(TM) Single Bond 2) and B (Prime & Bond NT) (n = 7). The microtensile bond strength (µTBS), fracture mode and bonding interface morphology of the specimens were evaluated via microtensile testing, stereo microscope and field emission scanning electron microscopy (FE-SEM) respectively after specimens being incubated in 37 °C water for 24 h. The immediate µTBS of C-ABC group bonding with adhesive A and B [(32.9±2.5) and (26.8±2.2) MPa] were significantly lower than that of the control group [(40.7±3.3) and (34.6±3.7) MPa] (P < 0.05). While the immediate µTBS of TRY group [(49.0 ± 3.6) and (44.5 ± 3.0) MPa] were significantly higher than that of the control group(P < 0.05). Dentin PG participates in the dentin bonding process. Removal of PG increased the immediate µTBS of dentin and total etching adhesives, while removal of GAG decreased the immediate µTBS.

An evaluation of deep-sea benthic megafauna length measurements obtained with laser and stereo camera methods

The 25 year time-series collected at Station M, ~4000m on the Monterey Deep-sea Fan, has substantially improved understanding of the role of the deep-ocean benthic environment in the global carbon cycle. However, the role of deep-ocean benthic megafauna in carbon bioturbation, remineralization and sequestration is relatively unknown. It is important to gather both accurate and precise measurements of megafaunal community abundance, size distribution and biomass to further define their role in deep-sea carbon cycling and possible sequestration. This study describes initial results from a stereo camera system attached to a remotely operated vehicle and analyzed using the EventMeasure photogrammetric measurement software to estimate the density, length and biomass of 10 species of mobile epibenthic megafauna. Stereo length estimates were compared to those from a single video camera system equipped with sizing lasers and analyzed using the Monterey Bay Aquarium Research Institute’s Video Annotation and Reference System. Both camera systems and software were capable of high measurement accuracy and precision (<±1mm measurement error and precision). However, the oblique angle of the single video camera caused the spatial scale of the image perspective to change with distance from the camera, resulting in error when measurements were not parallel or vertical to two horizontal-oriented scaling lasers. Analysis showed that the stereo system recorded longer lengths and higher biomass estimates than the single video camera system for the majority of the 10 megafauna species studied. The stereo image analysis process took substantially longer than the video analysis and the value of the EventMeasure software tool would be improved with developments in analysis automation. The stereo system is less influenced by object orientation and height, and is potentially a useful tool to be mounted on an autonomous underwater vehicle and for measuring deep-sea pelagic animals where the use of lasers is not feasible.

3-D object modeling from 2-D occluding contour correspondences by opti-acoustic stereo imaging

Utilizing in situ measurements to build 3-D volumetric object models under variety of turbidity conditions is highly desirable for marine sciences. To address the ineffectiveness of feature-based structure from motion and stereo methods under poor visibility, we explore a multi-modal stereo imaging technique that utilizes coincident optical and forward-scan sonar cameras, a so-called opti-acoustic stereo imaging system. The challenges of establishing dense feature correspondences in either opti-acoustic or low-contrast optical stereo images are avoided, by employing 2-D occluding contour correspondences, namely, the images of 3-D object occluding rims. Collecting opti-acoustic stereo pairs while circling an object, matching 2-D apparent contours in optical and sonar views to construct the 3-D occluding rim, and computing the stereo rig trajectory by opti-acoustic bundle adjustment, we generate registered samples of 3-D surface in a reference coordinate system. A surface interpolation gives the 3-D object model.In addition to the key advantage of utilizing range measurements from sonar, the proposed paradigm requires no assumption about local surface curvature as traditionally made in 3-D shape reconstruction from occluding contours. The reconstruction accuracy is improved by computing both the 3-D positions and local surface normals of sampled contours. We also present (1) a simple calibration method to estimate and correct for small discrepancy from the desired relative stereo pose; (2) an analytical analysis of the degenerate configuration that enables special treatment in mapping (tall) elongated objects with dominantly vertical edges. We demonstrate the performance of our method based on the 3-D surface rendering of certain objects, imaged by an underwater opti-acoustic stereo system.

Establishment and Evaluation of Scientific Research Personnel Stereo Training Mode-Based on Research Resource Planning

As a strategic resource in the development of medical research,research talents are the power that drives the sustainable development of a hospital.Hierarchical and stereo personnel training mode is established and based on the scientific resource planning which is aiming at different ages,different urhich is aiming at level of scientific research personnel's development needs,to promote the research of the discipline team especially the youth.It is evaluated with remarkable results. Key words: Research Resource Planning; Stereo Training Mode; Personnel Training; Medical Research

A New Stereoscopic (3D) Media Database and Teaching Strategy for Use in Large-Lecture Introductory Geoscience Courses

ABSTRACT Stereoscopic displays provide geoscience instructors with the ability to teach students the fundamental, and inherently three-dimensional, components of landforms and landscapes; yet the prevalence of such displays in higher education is limited. As costs of these systems continue to decrease, more instructors may wish to take advantage of stereoscopic display systems in their classroom. This paper serves as a guide for instructors who wish to install and use their own stereoscopic display systems using a case study conducted at the University of Kansas. The operational aspects covered include: creating stereo images, displaying stereoscopic images, selecting a stereoscopic display, and developing a new teaching strategy that incorporates the stereo system into the classroom environment. Additionally, a new database of stereoscopic media is provided to help promote the implementation of stereoscopic displays and free and open distribution of 3D teaching material.