Papers by Gianfranco Bianco
Recovering correct or at least realistic colors of underwater scenes is a very challenging issue ... more Recovering correct or at least realistic colors of underwater scenes is a very challenging issue for imaging techniques, since illumination conditions in a refractive and turbid medium as the sea are seriously altered. The need to correct colors of underwater images or videos is an important task required in all image-based applications like 3D imaging, navigation, documentation, etc. Many imaging enhancement methods have been proposed in literature for these purposes. The advantage of these methods is that they do not require the knowledge of the medium physical parameters while some image adjustments can be performed manually (as histogram stretching) or automatically by algorithms based on some criteria as suggested from computational color constancy methods. One of the most popular criterion is based on gray-world hypothesis, which assumes that the average of the captured image should be gray. An interesting application of this assumption is performed in the Ruderman opponent color space lαβ, used in a previous work for hue correction of images captured under colored light sources, which allows to separate the luminance component of the scene from its chromatic components. In this work, we present the first proposal for color correction of underwater images by using lαβ color space. In particular, the chromatic components are changed moving their distributions around the white point (white balancing) and histogram cutoff and stretching of the luminance component is performed to improve image contrast. The experimental results demonstrate the effectiveness of this method under gray-world assumption and supposing uniform illumination of the scene. Moreover, due to its low computational cost it is suitable for real-time implementation.
The 13th International Symposium on Virtual Reality, Archaeology and Cultural Heritage VAST (2012)
A. Gallo, A. Angilica, G. Bianco, F. De Filippo, M. Muzzupappa, B. Davidde, F. Bruno
Abstract... more A. Gallo, A. Angilica, G. Bianco, F. De Filippo, M. Muzzupappa, B. Davidde, F. Bruno
Abstract
The 3D reconstruction of underwater scenes is almost a requirement for a number of applications that need to
gather 3D data from fauna, flora or submerged structures. In the Cultural Heritage field, 3D models of finds and
archaeological sites are widely used, either for scientific research or for dissemination to the public. 3D imaging
techniques based on multi-view capture are a valid and effective tool in underwater applications, because they
require to capture the scene by different viewpoints using just one still or movie camera, installed on robots or
handled by a scuba diver. In this paper we test a technique for 3D reconstructions from images captured by multiple
views in a case study of submerged structures in the underwater archaeological site of Baia (Italy). This case study
is particularly critical due to the high level of turbidity, the heavy presence of marine flora and the changing of
lighting conditions, common in shallow water. All these disturbances cause a decrease of the contrast and an
alteration of the colours in the acquired images. The 3D model of a portion of the site has been reconstructed in
a virtual environment, both for studying and dissemination fruition purposes. In particular, a 3D application has
been developed in order to allow the exploration of the site, the measurement of the architectonical elements and
the simulation of the movements of a robot that performs specific operations of restoration and preservation.
Con il presente lavoro gli autori propongono una procedura per il calcolo delle deformazioni basa... more Con il presente lavoro gli autori propongono una procedura per il calcolo delle deformazioni basata sulla combinazione dei dati sperimentali ottenuti da una tecnica interferometrica, con la quale è stato misurato l'intero campo vettoriale di spostamento, ed una tecnica di ricostruzione 3D da immagini, con la quale è stata rilevata la forma della superficie analizzata. Il setup sperimentale col quale sono state applicate le due tecniche è un interferometro speckle dotato di quattro telecamere, mediante le quali il provino può essere osservato contemporaneamente da quattro differenti direzioni. La procedura proposta è stata applicata su una membrana a forma di calotta approssimativamente sferica sottoposta ad una pressione interna variabile. Tale tipologia di provino simula le prove che tipicamente vengono condotte sui segmenti anteriore e posteriore dell'occhio umano, al fine di identificare eventuali correlazioni con patologie più o meno direttamente causate dalle sollecitazioni meccaniche agenti su tali tessuti biologici.
The tree shrew (TS-tupaia glis belangeri) is increasingly used as animal model for myopia and gla... more The tree shrew (TS-tupaia glis belangeri) is increasingly used as animal model for myopia and glaucoma, where scleral biomechanics is known to play a key role. We aim to characterize the nonlinear mechanical response of 6 juvenile normal TS scleras to cyclic IOP.
Preconditioning by repeated cyclic loads is routinely used in ex vivo mechanical testing of soft ... more Preconditioning by repeated cyclic loads is routinely used in ex vivo mechanical testing of soft biological tissues. The goal of preconditioning is to achieve a steady and repeatable mechanical response and to measure material properties that are representative of the in vivo condition. Preconditioning protocols vary across studies, and their effect on the viscoelastic response of tested soft tissue is typically not reported or analyzed. We propose a methodology to systematically analyze the preconditioning process with application to inflation testing. We investigated the effect of preconditioning on the viscoelastic inflation response of tree shrew posterior sclera using two preconditioning protocols: (i) continuous cyclic loading-unloading without rest and (ii) cyclic loading-unloading with 15-min rest between cycles. Posterior scleral surface strain was measured using three-dimensional Digital Image Correlation (3D-DIC). We used five variables of characterizing features of the stress-strain loop curve to compare the two preconditioning protocols. Our results showed protocol-dependent differences in the tissue response during preconditioning and at the preconditioned state. Incorporating a resting time between preconditioning cycles significantly decreased the number of cycles (10.5 ± 2.9 cycles vs. 3.1 ± 0.5 cycles, p < 0.001) but increased the total time (15.8 ± 4.4 min vs. 51.2 ± 8.3 min, p < 0.001) needed to reach preconditioned state. At the preconditioned state, 2 of 5 characteristic variables differed significantly between protocols: hysteresis loop area (difference=0.023 kJ/m3, p = 0.0020) and elastic modulus at high IOPs (difference=24.0 MPa, p = 0.0238). Our results suggest that the analysis of the preconditioning process is an essential part of inflation experiments and a prerequisite to properly characterize the tissue viscoelastic response. Furthermore, material properties obtained at the preconditioned state can be impacted by the resting time used during preconditioning and may not be directly compared across studies if the resting time varies by 15 min between studies.
Historical documents often undergo various changes over time, that alter their original state and... more Historical documents often undergo various changes over time, that alter their original state and reduce their legibility. Digital techniques are widely applied for document preservation, archiving, analysis and dissemination over the Internet. The goal of restoration is to improve the document legibility for both human and automatic operators, to extract patterns and enhance colour reproduction. Our paper presents a framework for virtual restoration of ancient documents based on a combination of multispectral acquisition, 3D imaging and digital image analysis. The proposed framework consists of several steps. First, digital representations of the documents are acquired as multispectral images and 3D surface maps, the latter reconstructed by a structured light technique. A multispectral camera and a digital projector are used in triangular configuration for 2D and 3D data acquisition. Then the multispectral images are registered against possible misalignments, and the 3D surface representation is used to correct geometrical distortions. Document flattening is then performed by 3D surface parameterization and texture mapping. Statistical techniques of decorrelation are applied to extract individual context parts of the document patterns (stamp, text, etc.) and to attenuate interferences. The processed data are then binarized by the proper segmentation technique. The entire digital object history -all the acquisition and processing steps, with the corresponding parameters -is stored in metadata files. These data can be exploited in a future evaluation of the restoration process and can be used for either the creation of an expert knowledge database or the extraction of cross-document observations and conclusions.
We propose a system to process multispectral scans of double-sided documents. It can co-register ... more We propose a system to process multispectral scans of double-sided documents. It can co-register any number of recto and verso channel maps, and reduce the bleed-through/show-through distortions by exploiting blind source separation. From RGB scans, it is also able to recover the original colors, thus improving the readability of a document while maintaining its original appearance. The recto and verso patterns obtained can then be further analyzed. Many approaches to this problem are based on single-channel or multichannel recto-verso scans. In any case, getting rid of the unwanted interferences is a challenging problem. All the methods relying on pixel intensities, such as the one presented here, need a very accurate coregistration, and this is difficult for recto-verso pairs since the relevant information is often very sparse. * This work has been supported by the Project "Restarts"
This paper presents some experiments on different image processing techniques combined and adapte... more This paper presents some experiments on different image processing techniques combined and adapted to define a procedure aimed at improving the readability of ancient degraded documents. The focus is on documents affected by the bleed-through effect, which significantly reduces readability. The availability of the recto and verso scans of any single page is assumed. The proposed procedure is composed of three steps: recto-verso registration, image enhancement through statistical decorrelation and, finally, image segmentation. As the registration step can strongly influence the results obtained during the subsequent phases, we carried out a comparison of different registration algorithms, in order to evaluate their overall effectiveness on recto-verso processing.
Historical documents often undergo various changes over time, that alter their original state and... more Historical documents often undergo various changes over time, that alter their original state and reduce their legibility. Digital techniques are widely applied for document preservation, archiving, analysis and dissemination over the Internet. The goal of restoration is to improve the document legibility for both human and automatic operators, to extract patterns and enhance colour reproduction. Our paper presents a framework for virtual restoration of ancient documents based on a combination of multispectral acquisition, 3D imaging and digital image analysis. The proposed framework consists of several steps. First, digital representations of the documents are acquired as multispectral images and 3D surface maps, the latter reconstructed by a structured light technique. A multispectral camera and a digital projector are used in triangular configuration for 2D and 3D data acquisition. Then the multispectral images are registered against possible misalignments, and the 3D surface representation is used to correct geometrical distortions. Document flattening is then performed by 3D surface parameterization and texture mapping. Statistical techniques of decorrelation are applied to extract individual context parts of the document patterns (stamp, text, etc.) and to attenuate interferences. The processed data are then binarized by the proper segmentation technique. The entire digital object history -all the acquisition and processing steps, with the corresponding parameters -is stored in metadata files. These data can be exploited in a future evaluation of the restoration process and can be used for either the creation of an expert knowledge database or the extraction of cross-document observations and conclusions.
The 3D reconstruction of underwater scenes is almost a requirement for a number of applications t... more The 3D reconstruction of underwater scenes is almost a requirement for a number of applications that need to gather 3D data from fauna, flora or submerged structures. In the Cultural Heritage field, 3D models of finds and archaeological sites are widely used, either for scientific research or for dissemination to the public. 3D imaging techniques based on multi-view capture are a valid and effective tool in underwater applications, because they require to capture the scene by different viewpoints using just one still or movie camera, installed on robots or handled by a scuba diver. In this paper we test a technique for 3D reconstructions from images captured by multiple views in a case study of submerged structures in the underwater archaeological site of Baia (Italy). This case study is particularly critical due to the high level of turbidity, the heavy presence of marine flora and the changing of lighting conditions, common in shallow water. All these disturbances cause a decrease of the contrast and an alteration of the colours in the acquired images. The 3D model of a portion of the site has been reconstructed in a virtual environment, both for studying and dissemination fruition purposes. In particular, a 3D application has been developed in order to allow the exploration of the site, the measurement of the architectonical elements and the simulation of the movements of a robot that performs specific operations of restoration and preservation.
ISPRS Journal of Photogrammetry and Remote Sensing, 2011
This paper presents the experimental results of 3D underwater reconstructions based on a combinat... more This paper presents the experimental results of 3D underwater reconstructions based on a combination of structured light and stereo-photogrammetry. Structured lighting patterns are projected by a video projector and acquired by a stereo vision system for a whole-field 3D reconstruction. We describe the experimental setup used for the underwater tests in water tank, with different turbidity conditions. The quality of 3D reconstruction comes up to be acceptable even with high turbidity values, despite the heavy presence of scattering and absorption effects. In this work we have tested and analysed the results of a well-known optical technique -frequently used in air for industrial and Cultural Heritage applications -in underwater environment. We also tested the performance of this acquisition method for underwater applications with small field of view.
Journal of Cultural Heritage, 2013
ABSTRACT
Sensors, 2013
In some application fields, such as underwater archaeology or marine biology, there is the need t... more In some application fields, such as underwater archaeology or marine biology, there is the need to collect three-dimensional, close-range data from objects that cannot be removed from their site. In particular, 3D imaging techniques are widely employed for close-range acquisitions in underwater environment. In this work we have compared in water two 3D imaging techniques based on active and passive approaches, respectively, and whole-field acquisition. The comparison is performed under poor visibility conditions, produced in the laboratory by suspending different quantities of clay in a water tank. For a fair comparison, a stereo configuration has been adopted for both the techniques, using the same setup, working distance, calibration, and objects. At the moment, the proposed setup is not suitable for real world applications, but it allowed us to conduct a preliminary analysis on the performances of the two techniques and to understand their capability to acquire 3D points in presence of turbidity. The performances have been evaluated in terms of accuracy and density of the acquired 3D points. Our results can be used as a reference for further comparisons in the analysis of other 3D techniques and algorithms.
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2011
In the field of 3D scanning, there is an increasing need for more accurate technologies to acquir... more In the field of 3D scanning, there is an increasing need for more accurate technologies to acquire 3D models of close range objects. Underwater exploration, for example, is very hard to perform due to the hostile conditions and the bad visibility of the environment. Some application fields, like underwater archaeology, require to recover tridimensional data of objects that cannot be moved from their site or touched in order to avoid possible damages. Photogrammetry is widely used for underwater 3D acquisition, because it requires just one or two digital still or video cameras to acquire a sequence of images taken from different viewpoints. Stereo systems composed by a pair of cameras are often employed on underwater robots (i.e. ROVs, Remotely Operated Vehicles) and used by scuba divers, in order to survey archaeological sites, reconstruct complex 3D structures in aquatic environment, estimate in situ the length of marine organisms, etc. The stereo 3D reconstruction is based on the triangulation of corresponding points on the two views. This requires to find in both images common points and to match them (correspondence problem), determining a plane that contains the 3D point on the object. Another 3D technique, frequently used in air acquisition, solves this point-matching problem by projecting structured lighting patterns to codify the acquired scene. The corresponding points are identified associating a binary code in both images. In this work we have tested and compared two whole-field 3D imaging techniques (active and passive) based on stereo vision, in underwater environment. A 3D system has been designed, composed by a digital projector and two still cameras mounted in waterproof housing, so that it can perform the various acquisitions without changing the configuration of optical devices.
By the present paper, the authors propose an automated procedure for the acquisition of the 3D de... more By the present paper, the authors propose an automated procedure for the acquisition of the 3D deformation field of the human eye tissues that integrates, in the same apparatus, speckle interferometry and multi-view stereo reconstruction. In order to follow the evolution over time of the IOP-induced sclera mechanical deformations, we designed a custom laser speckle interferometer based on temporal phase-shifting and 4 digital cameras. Throughout the paper, the main features of the experimental apparatus and the performances in terms of accuracy and acquisition speed are reported and discussed in details.
Enhancement of underwater images and videos is an important task required in several image-based ... more Enhancement of underwater images and videos is an important task required in several image-based applications like survey, seafloor mapping, telepresence, documentation etc. Color correction or white balance of underwater images is the most challenging issue because of the highly-variable illumination conditions, increasing bluish shift with the depth. Another problem is the low image contrast with poorly visible details due to the scattering effects. This paper presents a fast enhancement method for non-uniformly illuminated underwater images. The method is based on the gray-world assumption applied in the Ruderman-lαβ opponent color space. The color correction is performed according to locally changing luminance and chrominance by using the summed-area table technique. Due to the low-complexity cost this method is suitable for real-time applications ensuring realistic colors of the objects, more visible details and enhanced visual quality.
We developed and optimized a custom dynamic Electronic Speckle Pattern Interferometer (d-ESPI) fo... more We developed and optimized a custom dynamic Electronic Speckle Pattern Interferometer (d-ESPI) for measuring time-dependent three-dimensional (3D) surface displacements during inflation testing of ocular tissues. The 3D displacement field was resolved under dynamic loading conditions for a simplified test case of a rubber phantom and a real-world test case of the posterior sclera of a human eye. We present the optical layout and calibration procedure of the d-ESPI, and demonstrate how the displacement field can be accurately resolved for specimen deformation rates up to 6 𝜇m/s.
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Papers by Gianfranco Bianco
Abstract
The 3D reconstruction of underwater scenes is almost a requirement for a number of applications that need to
gather 3D data from fauna, flora or submerged structures. In the Cultural Heritage field, 3D models of finds and
archaeological sites are widely used, either for scientific research or for dissemination to the public. 3D imaging
techniques based on multi-view capture are a valid and effective tool in underwater applications, because they
require to capture the scene by different viewpoints using just one still or movie camera, installed on robots or
handled by a scuba diver. In this paper we test a technique for 3D reconstructions from images captured by multiple
views in a case study of submerged structures in the underwater archaeological site of Baia (Italy). This case study
is particularly critical due to the high level of turbidity, the heavy presence of marine flora and the changing of
lighting conditions, common in shallow water. All these disturbances cause a decrease of the contrast and an
alteration of the colours in the acquired images. The 3D model of a portion of the site has been reconstructed in
a virtual environment, both for studying and dissemination fruition purposes. In particular, a 3D application has
been developed in order to allow the exploration of the site, the measurement of the architectonical elements and
the simulation of the movements of a robot that performs specific operations of restoration and preservation.
Abstract
The 3D reconstruction of underwater scenes is almost a requirement for a number of applications that need to
gather 3D data from fauna, flora or submerged structures. In the Cultural Heritage field, 3D models of finds and
archaeological sites are widely used, either for scientific research or for dissemination to the public. 3D imaging
techniques based on multi-view capture are a valid and effective tool in underwater applications, because they
require to capture the scene by different viewpoints using just one still or movie camera, installed on robots or
handled by a scuba diver. In this paper we test a technique for 3D reconstructions from images captured by multiple
views in a case study of submerged structures in the underwater archaeological site of Baia (Italy). This case study
is particularly critical due to the high level of turbidity, the heavy presence of marine flora and the changing of
lighting conditions, common in shallow water. All these disturbances cause a decrease of the contrast and an
alteration of the colours in the acquired images. The 3D model of a portion of the site has been reconstructed in
a virtual environment, both for studying and dissemination fruition purposes. In particular, a 3D application has
been developed in order to allow the exploration of the site, the measurement of the architectonical elements and
the simulation of the movements of a robot that performs specific operations of restoration and preservation.