Journal of Cultural Heritage 21 (2016) 904–909 Available online at ScienceDirect www.sciencedirect.com Case study Perceptual enhancement of degraded Etruscan wall paintings Davide Gadia a,∗ , Cristian Bonanomi a , Matilde Marzullo b , Alessandro Rizzi a a Department of Computer Science, University of Milano, Via Comelico 39, 20135 Milano, Italy b Department of Cultural Heritage and Environment, University of Milano, Via Festa del Perdono 7, 20122 Milano, Italy a r t i c l e i n f o Article history: Received 1 st February 2016 Accepted 13 April 2016 Available online 20 May 2016 Keywords: Contrast enhancement Cultural heritage Etruscan tombs Spatial color algorithms a b s t r a c t In this paper, we present a method for unsupervised digital image enhancement, finalized to the visual analysis of degraded Etruscan wall paintings. In many cases, original Etruscan wall paintings are not well-preserved and the simple photographic acquisition does not allow a successful visual investigation. The use of commercial softwares as image enhancers generally do not lead to satisfactory results. Here, we propose an algorithm based on a computational model of human vision, called Automatic Color Equalization (ACE). ACE allows an unsupervised filtering of the degraded wall paintings; it is able to equalize automatically color and contrast, allowing in this way an easier and more successful visual investigation. © 2016 Elsevier Masson SAS. All rights reserved. 1. Introduction and research aims The presented work is part of the broader Tarquinia Project [1], focused on the Etruscan Cultural Heritage that aims at investigating one of the major Etruscan cities known, UNESCO site since 2004 [2]. The project started more than 30 years ago, but its specific inter- disciplinary nature has been enriched and strengthened in the last ten years [3]. The common goal is the reconstruction of the archae- ological, cultural and historical dimension of the ancient Etruscan city with the integration of recent applications of computer science [3–11]. In the last years, the acquisition, elaboration, visualization and integration of digital images have become a crucial topic in the cultural heritage (CH) field. Practical use of digital images in CH spans between different research fields, like e.g. image processing, computer graphics, virtual reality, multimedia [12]. Digital images and image processing are at the base of the research, like e.g., acquisition of images in difficult conditions [13] or acquisition of material reflectance information [14], visualiza- tion of data from different imaging technologies [15], elaboration for enhanced visualization [16,17] or restoration [13,18–20] of degraded artifacts. Digital images can also be used as high reso- lution textures in computer graphics (CG) and virtual reality (VR) applications, to provide virtual access to CH sites with limited ∗ Corresponding author. Tel.: +390250314001. E-mail addresses: davide.gadia@unimi.it (D. Gadia), cristian.bonanomi@unimi.it (C. Bonanomi), matilde.marzullo@unimi.it (M. Marzullo), alessandro.rizzi@unimi.it (A. Rizzi). access [21–23], or to investigate different interpretations about the original placement or condition of CH sites or monuments [24–27]. In many of the latter cases, the problem to solve is the quality of the images, that need enhancement and preprocessing [28,29]. These new applications are intrinsically multidisciplinary and foster the interaction between the imaging scientists and the CH experts [3,30], as in the case of Tarquinia Project [1]. In this paper, we present an example of application of a perceptual-based unsupervised enhancement method to digital images acquired inside the Etruscan Necropolis of Tarquinia. This UNESCO site is an outstanding testimonial of the Etruscan culture, in which more than 6200 tombs carved in the rock have been discovered so far. Among them, around 140 are extraordinarily painted, and many hundreds more present traces of paintings [2]. Throughout the centuries, many paintings were detached from the walls, lost or destroyed, others are currently not visible due to the fading of the original colors. In most cases, the tombs are not acces- sible to the public, and, for reasons related to the preservation of the fragile paintings, also the visits for study purposes need to be avoided. Inside the tombs, natural light is not present, or is quite limited, while artificial light is often not adequate to achieve a full and detailed observation of the full painted walls. Thus, the use of digital images are of paramount importance. Therefore, several accurate sessions of photographic acquisition are carried out to collect many samples of each area that compose the inner parts of the tombs. The images are then processed to enhance details, and eventually stored in a multimedia database for supplemental studies and for dissem- ination. The chosen enhancement technique is critical for the final result. A suitable method should add no artefacts, it should be easy http://dx.doi.org/10.1016/j.culher.2016.04.009 1296-2074/© 2016 Elsevier Masson SAS. All rights reserved.