Roberto Scopigno

Global refinement of image-to-geometry registration for color projection on 3D models

The management, processing and visualization of color information is a critical subject in the context of the acquisition and visualization of real objects. Especially in the context of Cultural Heritage, artifacts are so complex or hard-to-handle that the appearance information has to be extracted from a set of images. The images usually have to be registered to the 3D model of the objects, in order to transfer the needed information. Hence, the problem of image-to-geometry registration has been thoroughly studied by the Computer Graphics and Computer Vision community. Several methods have been proposed, but a fully automatic and generic solution is still missing. Moreover, small misalignments often lead to visible artifacts in the final colored 3D models. In this paper, we propose a method to refine the alignment of a group of images which has been already registered to a 3D model. Taking advantage of the overlapping among the images, and applying a statistical global method based on Mutual Information, the registration error is distributed among all the elements of the dataset. Hence, the quality of color projection is improved, especially when dealing with small details. The method was tested on a number of heterogeneous Cultural Heritage objects, bringing to a visible improvement in the rendering quality. The method is fully automatic, and it does not need powerful hardware or long processing time. Hence, it represents a valid solution for a wide application on CH artifacts.

A compact representation of relightable images for the web

Relightable images have demonstrated to be a valuable tool for the study and the analysis of coins, bas-relief, paintings, and epigraphy in the Cultural Heritage (CH) field. Reflection Transformation Imaging (RTI) are the most diffuse type of relightable images. An RTI image consists in a per-pixel function which encodes the reflection behavior, estimated from a set of digital photographs acquired from a fixed view. Even if web visualization tools for RTI images are available, high fidelity of the relighted images still requires a high amount of data to be transmitted. To overcome this limit, we propose a web-friendly compact representation for RTI images which allows very high quality of the rendered images with a relatively small amount of data required (in the order of 6-9 standard JPEG color images). The proposed approach is based on a joint interpolation-compression scheme that combines a PCA-based data reduction with a Gaussian Radial Basis Function (RBF) interpolation. We will see that the proposed approach can be adapted also to other data interpolation schemes, and it is not limited to Gaussian RBF. The proposed approach has been compared with several techniques, demonstrating its superior performance in terms of quality/size ratio. Additionally, the rendering part is simple to implement and very efficient in terms of computational cost. This allows real-time rendering also on low-end devices.

From Paper to Web: Automatic Generation of a Web-Accessible 3D Repository of Pottery Types

3D web repositories are a hot topic for the research community in general. In the Cultural Heritage (CH) context, 3D repositories pose a difficult challenge due to the complexity and variability of models and to the need of structured and coherent metadata for browsing and searching. This paper presents one of the efforts of the ArchAIDE project: to create a structured and semantically-rich 3D database of pottery types, usable by archaeologists and other communities. For example, researchers working on shape-based analysis and automatic classification. The automated workflow described here starts from pages of a printed catalog, extracts the textual and graphical description of a pottery type, and processes those data to produce structured metadata information and a 3D representation. These information are then ingested in the database, where they become accessible by the community using dynamically-created web presentation pages, showing in a common context: 3D, 2D and metadata information. CCS Concepts •Computer Graphics → Shape modelling; •Data management systems → Database design and models; •Document management and text processing → Document capture;

The Dream and the Cross: a 3D-referenced, web-based digital edition

The Dream of the Rood is one of the earliest Christian poems in the corpus of Old English literature, and an example of the genre of dream poetry. While its complete text can be found in the 10th Century ”Vercelli Book”, the poem is considerably older, and its oldest occurrence is carved (in runes) on the 7-8th Century Ruthwell Stone Cross. In this paper, we present the prototype of a web-based digital edition of the Dream of the Rood, as it appears on the Ruthwell Cross. The multimedia framework presents the highly detailed 3D model acquired with 3D Scanning technology, together with the transcription and translation of the runes that can be found on its surface. The textual and spatial information are linked through a system of bi-directional links called spots, that give the possibility to the user to have a free navigation over the multimedia content, keeping the 3D and textual data synchronized. The proposed work provides discussion and solution on two main issues related to digital editions: the integration of three dimensional content in the context of the presentation on the web platform of heterogeneous multimedia data, and the creation of an XML encoding that could account for the necessities of 3D data disposition, but keeping the encoding rules in the context of the standards of the community.