## 5 Discussion and Conclusions  
The high pass layer has proven to be very efficient in automatically extracting the engraved stroke (Figure 5b). However, it presents a high level of noise, caused by the surface roughness of the limestone plaquette, which must be carefully eliminated. In this sense, having a previous final tracing of the figure is an advantage when it comes to distinguishing the engraved strokes (Figures 1b and 5e). We have found that the most superficial lines with a depth fewer than 10 microns do not appear reflected in the high pass layer. See how profile H shows on the jaw of the horse (Figure 8). A first groove 250 microns wide is observed with a depth fewer than 10 microns. However, the line to which this groove belongs is not reflected in the image above. In profile G, also belonging to the jaw, we see that the same line presents a groove with a width (0.5 mm) and greater depth (35 microns). In this case, the line is drawn on the image. This leads us to conclude that there will be uncertainty as to defining the beginning and/or end of the lines. In addition, the shallowest etched lines (depth fewer than 20 microns) can be represented in the high pass layer as dashed lines. We consider that the automatically extracted lines constitute a good working base from which to generate the engraved figure final drawing. According to [PERSON] et al. (2012), all recording techniques are flawed, so the level of uncertainty of a plot must be evaluated before any further analysis. This leads us to rely on other methods to validate questionable information and complete automatic traces. In our case, we will rely on other layers of information from our project (Figure 5). The DStretch-YRE layer has proven to be efficient in obtaining fine and superficial lines (Figure 5h), allowing us to validate and improve the broken or incomplete lines that we found in the high pass layer. It involves combining the results to create a single recording product. Furthermore, the DStretch-LYE layer makes it possible to distinguish incisions (post engraved strokes) and recent changes thanks to the differences in color caused by loss of patina (Figure 5j). The layer with the final tracing published in 1994 makes it possible to compare engraved strokes and a painted surface obtained by two different methods. The first by direct tracing on the piece and the second by indirect methods. In addition, it makes our work easier because it shows us the areas of interest (engraved strokes and pigment) and the conflictive areas to review. We believe that digitizing (and in our case georeferencing) printed graphic documentation produced using conventional techniques allows its review and updating, and its decomposition and adaptation to the various purposes of graphic documentation (research, conservation, and dissemination). Advantages of digital documentation compared to printed graphic documentation in itself constitute a punctual record that is difficult to review [30]. Combining the hillshade layer with the DStretch-LRE layer implies going from a 2D to a 3D record (see Figure 9). Allowing users to offer a volumetric reading not only of the support but also the motif. It is important to remark that, to delimit the pigment real extension in the image obtained with DStretch, it is necessary to manually remove those areas in which a false pigment identification occurs, either due to the different colorations of the support, the existence of dirt, or other reasons such as reddening and concretions. In addition, we understand that it is of great help to understand the why of certain lines, maximizing the objectivity. In the same way, combining the hillshade layer with the engravings (high pass layer) (Figures 8 and 10) makes it possible to study the relationship between the microrelief of the rock support and the figure. In our case, the surface irregularities also seem to participate in the figure of the horse [31]. The neck, located in a raised area (Figure 6), seems modelled thanks to the multiple contour lines (cf. profile I of Figure 8).