# Improved Application of Hyperspectral Analysis to Rock Art Panels from El Castillo Cave (Spain)
## 3 Results and Discussion
### Working Area  
This area is located in a place named the tunnel, on the left wall. There is a single small protrusion in what would be the roof. The motifs were made on limestone covered by a thin calcite layer. It consists of a tectiform or ideomorph of thick and intense red color, in a rectangular shape. The interior is very subdivided or compartmentalized. Around it there are some black pigment remains, among which no figure has been identified. The technical characterization tells us that this is a flat ink drawing, created using iron oxide. (Figure 7)  
Once the workflow is applied, some conclusions can be obtained:  
1. ICA and MNF analysis allow the isolation and identification of areas affected by calcite coating, to differing degrees, due to the decrease of signal intensity (Figure 8).  
Figure 7: True color composition of hyperspectral image and location of the extension of figures. (a) represents the location of Figure 8, (b) represents the location of Figure 10a, and (c) represents the location of Figure 10b (authorized by GIM Geomatics, S.L.).  
Different mineralogical compositions provide different spectral signals. In this case, areas of ochre and black have been distinguished under the calcite.
* Recovery of the pigments, even below the calcite layer: the limits of the figure are clearly defined, and the motif can be formally reconstructed thanks to the 2 nd PCA component (Figure 9) but also similar results can be obtained with MNF and ICA transformations.
* Extraction of underlying pigments under the calcite crust and the ochre pigment help reconstruct the painting sequence: in the image on the left you can see the legs of a goat and on the right the head of a female deer. (Figure 10).  
Classified data has been isolated and used to create the final tracing (Figure 11). After the assignment phase of the classification, the reliability of the results obtained must be assessed. This will give us an idea of the level of confidence we can have in the classification and check whether the objectives of the analysis have been met.  
The overall reliability of the classification was obtained by dividing the sum of the main diagonal by the total number of pixels. In the present paper, a comparison of the  
Figure 11: New tracing obtained by isolating pigment classes obtained after hyperspectral classification.  
Figure 10: (**a**) Detail of the extraction of underlying pigments under the calcite crust and the ochre pigment as described in [2]; (**b**) left-facing hind head located at the bottom of the panel.  
overall accuracy results shows that SAM classification performed the best with 89.075% (Table 1) overall classification accuracy, compared to 83.71% of the MTMF approach, so it was decided to keep the first results. The worst results occur in the class corresponding to thin calcite, as it is sometimes confused with the elements that underlie it.  
In our case, a comparison of the overall accuracy results shows that SAM classification performed the best with 75.00% overall classification accuracy, compared to 60.71% of the MTMF approach.