Fringe Projection Method for 3D High-Resolution Reconstruction of Oil Painting Surfaces

Abstract

The fringe projection (FP) method is an outstanding tool for reconstructing painted surfaces. This technique, which has been used for conservation and digitization, does not damage the artwork and can reach sub-millimeter accuracy. To carry out this type of analysis, it is necessary to achieve the most accurate measurements possible. Measuring the precision that a projector-camera-object arrangement can achieve is a complex task. In this paper, we show an experimental method used to measure the accuracy of this technique with instrumentation within the reach of most conservation laboratories. The method consists of capturing, as a reference model, a stepped cylindrical Nylamid® pyramid, as a construction whose shape, size, and manufacturing accuracy are known with high precision. The pyramid has eight well-defined steps, which are fashioned with an accuracy more exact than that of the fringe projection method. The height of each step was measured, obtaining the mean and variance of the height measurements fitted to a Gaussian distribution. In this work, we show the measured heights of the steps, obtained by varying the period of the fringes. The smallest detectable step height was less than 44.1 µm; however, this was obtained with a variance in the order of the step height. The smallest detectable step height with a small variance was 0.1008 mm. In addition to this accuracy measurement, a qualitative evaluation of a painting was carried out, finding the presence of possible superimposed thin layers, fabric, and microcracks, which commonly occur in the drying and aging processes. Further research would provide an experimental measurement of the method’s accuracy and its variance as essential for obtaining a confidence criterion that could then be applied to the model of the painting’s surface.

Fringe Projection Method’s Evolving Role in Cultural Asset Cataloging and Conservation: Potentiality in Testing Conservative Restoration Techniques

“…In the study conducted by [20], we experimentally determined the precision and depth variance of a specific system. The experiment involved using a camera and projector with slightly above-standard quality, and more technical details can be found in the manuscript Figure 3.…”

“…The unwrapped phase is essential to obtain the information of the object and then get the 3D digital model. This step is critical to getting accurate models, due to this, in literature exist a great number of algorithms to unwrap the phase [19,20]…”

“…Moreover, the resolution enables the observation of slight undulations on an almost flat background. This resolution allows us to observe and measure details related to conservation and technical aspects, such as brushstroke orientation, micro-fractures, and crack patterns, among others [20].…”

“…The methodology developed and previously tested by [20] will be applied to assess the quality and efficiency of conservation interventions. These interventions involve actions taken to preserve and protect cultural, historical, or artistic objects.…”