Image Processing & Applications

A system for orbital object monitoring is analyzed, based on a mid-latitude and an equatorial observatory. The enhancements with respect to the use of a single telescope located at mid-latitude, for space debris detection and tracking are highlighted in terms of surveying volume, object identification, and orbital determination accuracy. The need to improve observation capabilities in monitoring and cataloguing such kinds of objects is constantly growing, due to the constant increase of operative satellites and space debris in both geostationary Earth orbit (GEO) and low Earth orbit (LEO) regions. After the considerations on the feasibility of the whole system, an overview of the observatories' design is sketched, on the basis of previous Italian experience in space debris observation, and taking into account constraints imposed by the instrumentation. In particular the main characteristics of components, software for image analysis and observation methodologies are analyzed and a possible configuration is given, based on the ALMASCOPE observatory realized by the Space Robotics Group at the University of Bologna. This observatory was used for the 2010 test campaign carried out from the Broglio Space Center in Kenya. © 2014 IEEE.

A systematic characterisation of the porosity in the bulk and surface regions of a sintered Cr-Mo low alloy steel was carried out using image analysis. Fractional porosity in the different regions varies, mainly due to the scatter of the maximum pore size. A higher porosity is found in the bulk region and lower porosity in the regions that contact the die surface during compaction. The maximum pore size is larger in the bulk region than in the surface layers. The large pores are more irregular. With increasing green density, both the fractional porosity and maximum pore size decrease. The fraction of load bearing section in the bulk and surface regions was calculated from fractional porosity and the shape factor of the pores and compared in the different regions. The load bearing section fraction and the maximum pore size were used to predict tensile and fatigue resistance for different densities. The data from the characterisation of the bulk images can predict tensile strength. For fatigue, where the crack nucleates in the surface regions, the use of bulk data underestimates the fatigue resistance. © 2014 Elsevier Inc.

Keywords: Image analysis , Mechanical properties , Porosity , Sintered steels

In this article, a methodology to analyze the shear behavior of aluminum foam with closed cells is proposed. A biaxial load device was expressly designed and the elaboration with digital image correlation technique of the data acquired during the test with a charge coupled device (CCD) camera allowed determining the displacement and strain fields. This procedure made it possible to evaluate the procedure as suitable or not for conducting a shear characterization for metallic foam. The τ-γ curves obtained showed an initial elastic outline followed by the yield plateau, a peak load, and a rapid load drop. © 2014 Copyright Taylor & Francis Group, LLC.

Keywords: Aluminum foam , digital image correlation , shear characterization

Augmented reality (AR) applications rely on robust and efficient methods for tracking. Tracking methods use a computer-internal representation of the object to track, which can be either sparse or dense representations. Sparse representations use only a limited set of feature points to represent an object to track, whereas dense representations almost mimic the shape of an object. While algorithms performed on sparse representations are faster, dense representations can distinguish multiple objects. The research presented in this paper investigates the feasibility of a dense tracking method for rigid object tracking, which incorporates the both object identification and object tracking steps. We adopted a tracking method that has been developed for the Microsoft Kinect to support single object tracking. The paper describes this method and presents the results. We also compared two different methods for mesh reconstruction in this algorithm. Since meshes are more informative when identifying a rigid object, this comparison indicates which algorithm shows the best performance for this task and guides our future research efforts.

Cultural heritage is often not accessible to visually impaired and blind people, hardly ever when dealing with two-dimensional artworks like, for instance, paintings. In fact, despite tactile reproductions of 3D works of art such as sculptures or architectural models are quite common, a real barrier between blind people and pictorial artworks still exists, obviously due to their intrinsic 2D format. The translation of paintings into bas-relieves is recognized to be one of the most effective ways for breaking down such a barrier, thus allowing a sensible improvement in blind people's accessibility to this kind of works of art. Moving from these considerations, in this work the authors want to provide a bird's eye view on a new methodology for the semi-automatic generation of tactile 3D models starting from paintings, in particular those characterized by single-point perspective. The proposed method relies on an interactive Computer-based modelling procedure, which is conceived to be simple and effective to use. The procedure, which has been implemented into a prototypal software package, has been effectively used to 'translate' a set of paintings from the Italian Renaissance.

Design of new industrial objects characterized by high stylistic content often starts from sketches or images of the product to be, subsequently, represented in a 3D digital form by using CAD software. To speed up this phase, a number of methods for automatic or semi-automatic translation of sketches or images into a 3D model have been devised all over the world also for reverse engineering purposes. When the image shading is a crucial information for recovering the final 3D shape, Fast Marching is recognized to be among the best method to date, especially for frontally illuminated scenes. Unfortunately, such a method cannot be directly applied when object illumination in the considered image is oblique. The present work is aimed to propose a simple, but effective, approach for recovering 3D shape of objects starting from single side illuminated scenes i.e. for solving non-eikonal SFS problems. Tested against a set of case studies, the method proved its effectiveness. © (2014) Trans Tech Publications, Switzerland.

Keywords: Digital design , Fast marching , Intelligent manufacturing , Oblique illumination , Shape from shading

In the last years the development of interactive Computer-based methods for building virtual and physical 2.5D models from single shaded images faced with an exponential growth. In particular, a wide range of methods based on image processing-based procedures and on Shape From Shading (SFS) can be documented. On the basis of the most favorable techniques devised in literature, the present work describes an improved interactive method capable of retrieving 2.5D models using image shading information. The pro-posed method performs a SFS-based reconstruction where (1) the overall geometry of the expected surface is first recovered and (2) the final 2.5D reconstruction is obtained by minimizing a suitable functional using the rough surface as an initialization function. The method improves previous interactive works by introducing a novel two-step rough surface recovery and a new definition of a functional to be minimized for solving the SFS problem. Tested against a set of case studies the proposed method proves to be effective in providing 2.5D models. © 2014 Science Publications.

Keywords: 2.5D model , Image processing , Interactive reconstruction , Minimization , Shape from shading

The visual appearance of seamless dyed edges of luxury leather goods represents a key issue in terms of quality grading since a high-quality leather has to be characterised by homogeneously coloured and shaped edges with uniform ink thickness. Despite a huge literature produced by scientific and technical community to automate many leather manufacturing processes, since leather patches are often characterised by a free-form shape, any attempt of automating leather edges dyeing produced unsatisfactory and inaccurate results. In order to overcome the drawbacks of the existing approaches, the main objective of the present work is to provide a computer-based system for automatically dyeing leather patches edges. The described system includes: 1) a machine vision (MV) hardware equipment, consisting of both illumination and a high resolution acquisition device, devoted to patches edge detection; 2) a pantograph whose dyeing tool is moved along leather edges; 3) a series of computer-based methods for the automatic extraction of the leather patches outlines. Extensive testing performed using the developed machine demonstrated its effectiveness in delivering fast, automatic and high quality edge finishing in a reliable and repeatable way. © 2014 Inderscience Enterprises Ltd.

Keywords: Leather dyeing , Machine vision , Process automation

Over the last few years, technologies like 3D scanning and rapid prototyping provided an extraordinary boost in improving reproductions of 3D artworks, like sculptures and historical buildings, all over the world. Physical 3D reproduction of subjects represented in paintings, is recognised to be one of the best ways to allow visually impaired people to enjoy such kind of artworks. However, the use of advanced technologies with the aim of realising 3D models starting from paintings has not been satisfactorily investigated yet. Though a number of algorithms coming from computer vision science exist to cope with similar issues, the specific problem of producing a 3D representation which is targeted at blind people tactile exploration has been only marginally investigated. Starting from these considerations, this work presents 1) a quite extensive review of the criteria proposed in literature for producing tactile models suitable for blind people and 2) four alternative computer-based methods for semi-automatic generation of tactile 3D models starting from RGB digital images of paintings. The outcomes of this study contribute new information to the field of visually impaired user-oriented 3D reconstruction and clearly indicate the strategy to be adopted in order to produce a meaningful reproduction of a bi-dimensional piece of artwork. © 2014 Inderscience Enterprises Ltd.

Keywords: 3D computer-based modelling , Blind , Haptic exploration , Visually impaired

The face is perhaps the most important human anatomical part, and its study is very important in many fields, such as the medical one and the identification one. Technical literature presents many works on this topic involving bi-dimensional solutions. Even if these solutions are able to provide interesting results, they are strongly subjected to images distortion. Thanks to the significant improvements obtained in the 3D scanner domain (photogrammetry for instance), today it is possible to replace the 2D images with more precise and complete 3D models (triangulated points clouds). Working on three-dimensional data, in fact, it is possible to obtain a more complete set of information about the face morphology. At present, even if it is possible to find interesting papers on this field, there is the lack of a complete protocol for converting the big amount of data coming from the three-dimensional point clouds in a reliable set of facial data, which could be employed for recognition and medical tasks. Starting from some anatomical human face concepts, it has been possible to understand that some soft-tissue landmarks could be the right data set for supporting many processes working on three-dimensional models. So, working in the Differential Geometry domain, through the Coefficients of the Fundamental Forms, the Principal Curvatures, Mean and Gaussian Curvatures and also with the derivatives and the Shape and Curvedness Indexes, the study has proposed a structured methodology for soft-tissue landmark formalization in order to provide a methodology for their automatic identification. The proposed methodology and its sensitivity have been tested with the involvement of a series of subjects acquired in different scenarios. © 2012 Springer Science+Business Media, LLC.

Keywords: 3D models , 3D scanners , Face morphology , Soft tissue landmarks

An important issue related to future nuclear fusion reactors fueled with deuterium and tritium is the creation of large amounts of dust due to several mechanisms (disruptions, ELMs and VDEs). The dust size expected in nuclear fusion experiments (such as ITER) is in the order of microns (between 0.1 and 1000 μm). Almost the total amount of this dust remains in the vacuum vessel (VV). This radiological dust can re-suspend in case of LOVA (loss of vacuum accident) and these phenomena can cause explosions and serious damages to the health of the operators and to the integrity of the device. The authors have developed a facility, STARDUST, in order to reproduce the thermo fluid-dynamic conditions comparable to those expected inside the VV of the next generation of experiments such as ITER in case of LOVA. The dust used inside the STARDUST facility presents particle sizes and physical characteristics comparable with those that created inside the VV of nuclear fusion experiments. In this facility an experimental campaign has been conducted with the purpose of tracking the dust re-suspended at low pressurization rates (comparable to those expected in case of LOVA in ITER and suggested by the General Safety and Security Report ITER-GSSR) using a fast camera with a frame rate from 1000 to 10,000 images per second. The velocity fields of the mobilized dust are derived from the imaging of a two-dimensional slice of the flow illuminated by optically adapted laser beam. The aim of this work is to demonstrate the possibility of dust tracking by means of image processing with the objective of determining the velocity field values of dust re-suspended during a LOVA. © 2014 Elsevier B.V.

Keywords: Computer vision , Dust tracking , Nuclear fusion plants , Particle image velocimetry (PIV) , Safety , Security

In the field of dental health care, plaster models combined with 2D radiographs are widely used in clinical practice for orthodontic diagnoses. However, complex malocclusions can be better analyzed by exploiting 3D digital dental models, which allow virtual simulations and treatment planning processes. In this paper, dental data captured by independent imaging sensors are fused to create multi-body orthodontic models composed of teeth, oral soft tissues and alveolar bone structures. The methodology is based on integrating Cone-Beam Computed Tomography (CBCT) and surface structured light scanning. The optical scanner is used to reconstruct tooth crowns and soft tissues (visible surfaces) through the digitalization of both patients' mouth impressions and plaster casts. These data are also used to guide the segmentation of internal dental tissues by processing CBCT data sets. The 3D individual dental tissues obtained by the optical scanner and the CBCT sensor are fused within multi-body orthodontic models without human supervisions to identify target anatomical structures. The final multi-body models represent valuable virtual platforms to clinical diagnostic and treatment planning. © 2013 by the authors; licensee MDPI, Basel, Switzerland.

Keywords: Dental CBCT images , Optical scanning , Orthodontic model , Sensor fusion , Tooth segmentation

Wheel alignment, consisting of properly checking the wheel characteristic angles against vehicle manufacturers' specifications, is a crucial task in the automotive field since it prevents irregular tyre wear andaffects vehicle handling and safety. In recent years, systems based on Machine Vision have been widely studied in order to automatically detect wheels' characteristic angles. In order to overcome the limitations of existing methodologies, due to measurement equipment being mounted onto the wheels, the present work deals with design and assessment of a 3D machine vision-based system for the contactless reconstruction of vehicle wheel geometry, with particular reference to characteristic planes. Such planes, properly referred to as a global coordinate system, are used for determining wheel angles. The effectiveness of the proposed method was tested against a set of measurements carried out using a commercial 3D scanner; the absolute average error in measuring toe and camber angles with the machine vision system resulted in full compatibility with the expected accuracy of wheel alignment systems. © 2013 Furferi et al.

Keywords: Machine vision , Stereovision , Wheel alignment

We present an overview of methods and applications of automatic characterization of the appearance of materials through colour and texture analysis. We propose a taxonomy based on three classes of methods (spectral, spatial, and hybrid) and discuss their general advantages and disadvantages. For each class we present a set of methods that are computationally cheap and easy to implement and that was proved to be reliable in many applications. We put these methods in the context of typical industrial environments and provide examples of their application in the following tasks: surface grading, surface inspection, and content-based image retrieval. We emphasize the potential benefits that would come from a wide implementation of these methods, such as better product quality, new services, and higher customer satisfaction. © 2013 Elena González et al.

Automatic detection and assessment of dirt particles in pulp and paper plays a pivotal role in the papermaking industry. Traditional visual inspection by human operators is giving the way to machine vision, which provides many potential advantages in terms of speed, accuracy and repeatability. Such systems make use of image processing algorithms which aim at separating paper and pulp impurities from the background. The most common approach is based on image thresholding, which consists of determining a set of intensity values that split an image into one or more classes, each representing either the background (i.e.: An area with no defects) or an area with some types of contraries. In this paper we present a quantitative experimental evaluation of four image thresholding methods (i.e.: Otsu's, Kapur's, Kittler's and Yen's) for dirt analysis in paper. The results show that Kittler's method is the most stable and reliable for this task. © 2013 DIME UNIVERSITÀ DI GENOVA.

Keywords: Image thresholding , Machine vision , Paper , Quality assessment

In this paper we consider the problem of colour-based sorting hardwood parquet slabs into lots of similar visual appearance. As a basis for the development of an expert system to perform this task, we experimentally investigate and compare the performance of various colour descriptors (i.e.: soft descriptors, percentiles, marginal histograms and 3D histogram), and colour spaces (i.e.: RGB, HSV and CIE Lab). The results show that simple and compact colour descriptors, such as the mean of each colour channel, are as accurate as more complicated features. Likewise, we found no statistically significant difference in the accuracy attainable through the colour spaces considered in the paper. Our experiments also show that most methods are fast enough for real-time processing. The results suggest the use of simple statistical descriptors along with RGB data as the best practice to approach the problem. © 2012 Elsevier Ltd. All rights reserved.

Keywords: Colour descriptors , Grading , Parquet , Sorting , Wood

The aim of this paper is to describe a general framework for texture analysis which we refer to as the HEP (histograms of equivalent patterns). The HEP, of which we give a clear and unambiguous mathematical definition, is based on partitioning the feature space associated to image patches of predefined shape and size. This task is approached by defining, a priori, suitable local or global functions of the pixels' intensities. In a comprehensive survey we show that diverse texture descriptors, such as co-occurrence matrices, gray-level differences and local binary patterns, can be seen all to be examples of the HEP. In the experimental part we comparatively evaluate a comprehensive set of these descriptors on an extensive texture classification task. Within the class of HEP schemes, improved local ternary patterns (ILTP) and completed local binary patterns (CLBP) emerge as the best of parametric and non-parametric methods, respectively. The results also show the following patterns: (1) higher effectiveness of multi-level discretization in comparison with binarization; (2) higher accuracy of parametric methods when compared to non-parametric ones; (3) a general trend of increasing performance with increasing dimensionality; and (4) better performance of point-to-average thresholding against point-to-point thresholding. © 2012 Springer Science+Business Media, LLC.

Keywords: BGC , Image classification , LBP , LTP , Texture features

Foams and porous materials with cellular structure have many interesting combinations of physical and mechanical properties coupled with low specific weight. By means of replication casting it is possible to manufacture foams from molten metal without direct foaming. A soluble salt is used as space holder, which is removed by leaching in water. This can be done successfully if the content of space holding fillers is so high that all the granules are interconnected. One of the main advantages of using the replication casting is a close control of pore sizes which is given by the distribution of particle sizes of the filler material. This contrasts with the pore size distribution of the materials foamed by other processes where a wider statistical distribution of pores is found. On the other hand, the maximum porosities that can be achieved using space holders are limited to values below 60%, whereas the other methods allow for porosities up to 98%. Temperature of the mould and infiltration pressure are critical process parameters: a typical problem encountered is the premature solidification of the melt, especially due to the high heat capacity of the salt. In this work foam properties such as cell shape, distribution and anisotropy and defect presence are investigated by using digital image processing technique. For this purpose replicated AlSi7Mg0.3 alloy foams are produced by infiltrating preforms of NaCl particles, varying the metal infiltration pressure and the mould preheating temperature. An original procedure based on image analysis has been set up to determine size, morphology and distribution of cells. The paper demonstrates that this methodology, coupled with microstructural analysis, is a useful tool for investigating the effects of process parameters on foam properties.

Keywords: Aluminium foams , Foam morphology , Image analysis , Replication casting , Watershed method

3D topological segmentation entails the partition of 3D clouds of connected voxels (e.g. 3D images) into sets of entities, connected by a series of nodes. Especially for thread-like structures (e.g. blood vessels, proteins, piping and voxel-based 3D sketches), nodes detection and, more in particular, identification of entities converging in a node may be considered a crucial issue to correctly interpret the "structure" of the analysed object. The main objective of the present work is to describe an innovative algorithm able to determine the possible intersection zones between groups of voxels composing a thread-like 3D voxel cloud. The devised algorithm is based on a multi-directional ray-tracing procedure applied, for each voxel of the 3D dataset, with reference to a set of directions defined by an appropriate 3D neighbourhood domain. The thread-like structure thicknesses, coming from the ray-trace analysis, are estimated along different directions. Finally, the set of thicknesses is analysed by means of a statistical approach so that voxels, possibly belonging to intersection zones, can be identified. The proposed algorithm demonstrated its effectiveness in a number of test cases. Copyright © 2013 Binary Information Press.

Keywords: 3D topology , Local thickness , Ray-trace analysis , Voxel graphics