Effects of different coating materials on three-dimensional optical scanning accuracy

Abstract

The processes of three-dimensional optical scanning depend on the reflection of the surface to be digitized. To scan specular or translucent surfaces, it is necessary to apply a coating material which interferes with the accuracy of the three-dimensional measurements. This study proposes the use of gold, silver, platinum, and carbon by sputtering to coat the surfaces to be scanned. The effects of these materials on the accuracy of the three-dimensional scanning were evaluated and compared with those of two frequently used materials, namely, talc and non-aqueous wet developer for penetrant testing. To verify the resulting geometric variations, specimens were scanned before and after the application of each coating material. The results showed that the intrinsic errors of the three-dimensional scanning process, such as the registration of several point clouds, can have more significant effects than the coating material used. Measurements taken from a single point cloud showed dimensional tolerances of approximately 0.01 mm for gold, platinum, and carbon coating. These coatings offer significantly higher accuracy than the traditionally used developer and are suggested for accurate three-dimensional scanning of specular and translucent surfaces.

Exploiting Light Directionality for Image‐Based 3D Reconstruction of Non‐Collaborative Surfaces

“…To reduce the negative effect of specular reflections, cross polarisation (Nicolae et al., 2014; Menna et al., 2016) and image pre‐processing methods (Wallis, 1976; Gaiani et al., 2018; Calantropio et al., 2020) have also been used. Another popular solution is to spray a thin layer of white or coloured powder (Palousek et al., 2015; Lin et al., 2017; Mousavi et al., 2018; Pereira et al., 2019). However, coating an object with powder may not always be possible, neither with sensitive cultural heritage measurements nor in real‐time 3D inspection of industrial components.…”

“…However, coating an object with powder may not always be possible, neither with sensitive cultural heritage measurements nor in real‐time 3D inspection of industrial components. Moreover, the added layer could increase the overall volume of the object and may smooth out small details (Palousek et al., 2015; Pereira et al., 2019).…”

Combining Photogrammetry and Photometric Stereo to Achieve Precise and Complete 3D Reconstruction

“…However, these procedures may smooth off surface roughness or vary the texture from one view to the next, negatively affecting the results [ 11 ]. Another common approach to spray the surface with a thin layer of white or colored powder [ 1 , 2 , 25 , 40 , 41 , 42 ] can also be used as a common solution. However, powdering the object surface might be impractical when the real topography of an object is needed at high-resolution since the layer added increases the total object volume and can smooth out minor information.…”

Investigating 3d Reconstruction of Non-Collaborative Surfaces Through Photogrammetry and Photometric Stereo

“…These methods, however, assume that the object surface is Lambertian, which is not the case with objects that have specular reflection or interreflection effects. Another popular method for reducing the reflectivity of complex objects is to coat the surface with a thin layer of white or colored powder (Ackermann et al, 2008;Hosseininaveh et al, 2015;Palousek et al, 2015;Lin et al, 2017;Mousavi et al, 2018;Pereira et al, 2019). However, in some cases, such as for delicate cultural heritage measurements or in-line inspection of industrial components, such surface treatment might not be practical.…”

“…However, in some cases, such as for delicate cultural heritage measurements or in-line inspection of industrial components, such surface treatment might not be practical. Furthermore, the added layer can increase the object's size or hide geometric details such as defects on the surface (Palousek et al, 2015;Pereira et al, 2019).…”