Digital imaging techniques for recording and analysing prehistoric rock art panels in Galicia (NW Iberia)

Abstract

Several works have highlighted the relevance of 3D modelling techniques for the study of rock art, especially in case of deteriorated state of preservation. This paper presents a methodological approach to accurate document two Bronze Age rock art panels in Galicia (Spain), using photogrammetry SfM. The main aim is to show the application of digital enhancement techniques which have allowed the accurate depiction of the motifs and the correction of previous calques, focusing on the application of the exaggerated shading as a novel analytical method.

An accessible, agile and low‐cost workflow for 3D virtual analysis and automatic vector tracing of engravings: Atlantic rock art analysis

“…The technique described in Carrero‐Pazos et al () was applied in this case to the raster files obtained as a result of the previous step. This technique, which consists of submitting the image to low exposure and subsequent overexposure by means of the dodging and burning tools in Photoshop, was carried out, the only difference being that the free software GIMP was chosen for this task.…”

“…Other more advanced methods, such as polynomial texture mapping (Malzbender, Gelb, & Wolters, ), also termed reflectance transformation imaging (RTI) (Díaz‐Guardamino & Wheatley, ; Domingo, Villaverde, López‐Montalvo, Lerma, & Cabrelles, ; Duffy et al, ; Earl, Martinez, & Malzbender, ; Mudge et al, , ), which are based on a change analysis of the lighting point in an image collection to detect the geometric details of the surface, have expanded and represent an important advance in the analysis of rock art engravings. Other workflows originating from the computer graphics community (Pires, Rubio, & Arana, ; Saito & Takahashi, ) – specifically, radiance scaling shaders, which are based on the morphological analysis of 3D models that are described in Vergne, Pacanowski, Barla, Granier, and Schlick (), Vergne, Pacanowski, Barla, Granier, and Reuter () and are used for engraving detection in Carrero‐Pazos, Vilas‐Estévez, and Vázquez‐Martínez (), López‐Menchero Bendicho, Marchante Ortega, Vincent, Cárdenas Martín‐Buitrago, and Onrubia Pintado () and Medici and Rossi () – have shown great potential for accomplishing this task. The software applications MeshLab (Visual Computing Lab, ISTI‐CNR, Italy), (Vergne et al, ) and Xshade (exaggerated shading for depicting shape and detail) (Rusinkiewicz, Burns, & DeCarlo, ) are used in these cases to enhance 3D models with similar results.…”

“…Automatic image vectorization such as edge detection on cave paintings is shown in Clogg, Dίaz‐Andreu, and Larkman (), Harmon (), Mark and Billo () and Mas Cornellà, Maura Mijares, Solís Delgado, and Pérez González (), where different automatic vectorization techniques of rock paintings are analysed from digital images such as decorrelation stretch; automatic vectorization techniques have also been used with rock engravings, as shown in Ortiz‐Sanz et al (). Recently, a previous treatment of two‐dimensional (2D) captures based on holding back light (dodging) or increasing the exposure (burning) was described in Carrero‐Pazos, Vilas‐Estévez, and Vázquez‐Martínez (), generating a result that improves and facilitates subsequent vectorization, which can be performed easily using free online resources such as Vectorizer, Online‐Convert or Vector Magic (Godfrey & Eveleth, ; Lacroix, ).…”

On the Combination of Remote Sensing and Geophysical Methods for the Digitalization of the San Lázaro Middle Paleolithic Rock Shelter (Segovia, Central Iberia, Spain)

“…Orthophotography: (Present and historical) in order to find signs of anthropic activity (e.g., wall alignments, differential growth in crops that reveal geometric figures, etc.) Digital Elevation Model: used with the aim of detecting characteristic elements on the "z" axis (e.g., elevations, rocks alignments, that in view of a human eye are not perceptible in the terrain) Site contextualization and documentation: phase of data collection of the site for its understanding [20][21][22][23][24][25].…”

Tailoring 3D modelling techniques for epigraphic texts restitution. Case studies in deteriorated roman inscriptions

“…3 All of them are benefit from the accuracy obtained by 3D modelling techniques, increasing the precision of results compared to regular bidimensional pictures or hand-made models (Guidi et al 2014: 55). However, the possibilities of DIM by far surpasses the dissemination of archaeological artefacts, being the basis of new researches which aim to virtually enhance the grooves in order to better read the motifs (see e.g., Correia Santos et al 2014;Frasson 2014;Pires et al 2014a;Carrero-Pazos et al 2018). This would be of great help in Galicia (NW of Iberian Peninsula), where the systematization works of the currentlyknown Roman inscriptions made by scholars such as G. Pereira Menaut or A.…”