Luca Puggelli

Improving surface reconstruction in shape from shading using easy-to-set boundary conditions

Minimisation techniques are commonly adopted methodologies for retrieving a 3D surface starting from its shaded representation (image), i.e., for solving the widely known shape from shading (SFS) problem. Unfortunately, depending on the imaged object to be reconstructed, retrieved surfaces often results to be completely different from the expected ones. In recent years, a number of interactive methods have been explored with the aim of improving surface reconstruction; however, since most of these methods require user interaction performed on a tentative reconstructed surface which often is significantly different from the desired one, it is advisable to increase the quality of the surface, to be further processed, as much as possible. Inspired by such techniques, the present work describes a new method for interactive retrieving of shaded object surface. The proposed approach is meant to recover the expected surface by using easy-to-set boundary conditions, so that the human-computer interaction primaril...

From 2D to 2.5D i.e. from painting to tactile model

Display Omitted Commonly used to produce the visual effect of full 3D scene on reduced depth supports, bas relief can be successfully employed to help blind people to access inherently bi-dimensional works of art. Despite a number of methods have been proposed dealing with the issue of recovering 3D or 2.5D surfaces from single images, only a few of them explicitly address the recovery problem from paintings and, more specifically, the needs of visually impaired and blind people.The main aim of the present paper is to provide a systematic method for the semi-automatic generation of 2.5D models from paintings. Consequently, a number of ad hoc procedures are used to solve most of the typical problems arising when dealing with artistic representation of a scene. Feedbacks provided by a panel of end-users demonstrated the effectiveness of the method in providing models reproducing, using a tactile language, works of art otherwise completely inaccessible.

Digital Bas-Relief Design: a Novel Shape from Shading-Based Method

Design of products characterized by high stylistic content and organic shapes in the form of bas-relief (e.g. fashion accessories, commemorative plaques and coins) is traditionally performed starting from handmade drawings or photographs that are manually reproduced by highly skilled craftsmen such as sculptors and engravers and finally digitized by means of 3D scanning. Several Computer-based procedures have been devised with the aim of speeding up this process, which is considerably time consuming, subjective and costly; these are mainly based on image processing techniques such as embossing, enhancement, histogram equalization or dynamic range, also implemented in CAD-based commercial software. However, these approaches are characterized by several limitations preventing them from providing a “correct” final geometry. In view of that, the present work describes a novel method for the creation of digital bas-reliefs from a single image using a Shape From Shading (SFS) based approach with interactive ini...

Analysis of deformations induced by manufacturing processes of fine porcelain whiteware

During sintering, porcelain changes its phase composition as well as its physical and mechanical properties. The most evident effect of these transformations is a significant change of shape, which is a combination of shrinkage and pyroplastic deformations, caused by softening. Both of these phenomena are induced by temperature, which is on its turn influenced by several variable factors that are difficult to predict. Especially for products manufactured in large scale, the resulting shape of artefacts may significantly vary even among the same batch. Consequently, for companies demanding high quality standard, this variability entails a high number of rejected products. For this reason, the present work aims at investigating the amount of variation introduced by firing process for an actual industrial product, independently from other (more or less) known variation sources such as the ones related to materials and forming processes. This could help process engineers to focus their attention when trying to improve the quality of final products.

Tactile exploration of paintings: An interactive procedure for the reconstruction of 2.5D models

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 peoples accessibility to this kind of works of art. Moving from these considerations, in this work the authors want to provide a birds 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.

Original strategy for avoiding over-smoothing in SFS problem resolution

With the aim of retrieving 3D surfaces starting from single shaded images, i.e. for solving the widely known shape from shading problem, an important class of methods is based on minimisation techniques where the expected surface to be retrieved is supposed to be coincident with the one that minimise a properly developed functional, consisting of several contributions. Despite several different contributes that can be explored to define a functional, the so called ‘smoothness constraint’ is a cornerstone since it is the most relevant contribute to guide the convergence of the minimisation process towards a more accurate solution. Unfortunately, in case input shaded image is characterised by areas where actual brightness changes rapidly, such a constraint introduces an undesired over-smoothing effect for the retrieved surface. The present work proposes an original strategy for avoiding such a typical over-smoothing effect, with regard to the image regions in which this is particularly undesired such as, for instance, zones where surface details are to be preserved in the reconstruction. The proposed strategy is tested against a set of case studies and compared with other traditional SFS-based methods to prove its effectiveness.

Two Simple Yet Effective Strategies for Avoiding Over-Smoothing in SFS Problem

Minimization techniques are widely used for retrieving a 3D surface starting from a single shaded image i.e., for solving the shape from shading problem. Such techniques are based on the assumption that expected surface to be retrieved coincides with the one that minimize a properly developed functional, consisting of several contributions. Among the possible contributes defining the functional, the so called “smoothness constraint” is always used since it guides the convergence of the minimization process towards a more accurate solution. Unfortunately, in areas where actually brightness changes rapidly, it also introduces an undesired over-smoothing effect. The present work proposes two simple yet effective strategies for avoiding the typical over-smoothing effect, with regards to the image regions in which this effect is particularly undesired (e.g., areas where surface details are to be preserved in the reconstruction). Tested against a set of case studies the strategies prove to outperform traditional SFS-based methods.

IMPROVED INTERACTIVE METHOD FOR RECO-VERING 2.5D MODELS FROM SINGLE IMAGES

In the last years the development of interactive Co mputer-based methods for building virtual and physical 2.5D models from single shaded images face d 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 f avorable techniques devised in literature, the present work describes an improved interactive meth od 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 s urface 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 solv ing the SFS problem. Tested against a set of case studies the proposed method proves to be effective in providing 2.5D models.

Different Strategies for Rapid Prototyping of Digital Bas-Reliefs

In the last decades several computer-based procedures have been devised with the aim of speeding up the 3D reconstruction from a single image in the form of bas-relief. At the same time, the use of rapid prototyping (RP) technology considerably spread enabling quick manufacture of 3D products directly from 3D modelling systems. The present paper presents a few consideration about different possible strategies for bas-reliefs manufacturing by using the main RP techniques (stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM) and Polyjet/Multi-jet technology). A practical example is used for discussing pros and cons of the different alternatives.

A Practical Approach Based on Shape from Shading and Fast Marching for 3D Geometry Recovery under Oblique Illumination

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.