## 4 Tests
After proving the effectiveness of the calibration process in a standard situation, such as correcting the illumination of a cyclorama that has been affected by its use, it was necessary to test its validity to detect severe artifacts that could affect decisively the chroma-keying quality. For this purpose, we created four configurations with distorted illumination and known characteristics to check if both the visual and statistical results were able to detect them. The first artifact consisted on using a spot light to create a very over lighted area in the right part of the cyclorama. Both the visual and statistical results were analyzed. Visually, there is a concentration of small regions around the spot light and many centroids with more than one centroid correspondence in that area (Figure 11a). This is corroborated by the data shown in Figure 12, where around 20% of the ideal centroids have a correspondence of more than 1 real centroid, a percentage that doubles the previous tests where the artifacts were much subtler. Figure 11: Images of the four tests performed: right spot light (**a**), center right spot light (**b**), center light (**c**) and left light (**d**). The images represent the 512 regions subdivision (**left**) and the centroid correspondence (**right**). The coefficient of variation of the regions area shows the big differences existing between the small regions in the over lighted surface and the big ones in the rest of the cyclorama. As a result, the values go from 41.4% for 64 regions and 45.8% in the 1024 configuration (Figure 13). This means that the average difference between the region areas is of almost half the area of the ideal region size. Figure 12: Number of correspondences (centroids which are closer) between each ideal centroid and the real ones (**a**). Standard deviation and average distance from the centroid to the geometrical center of the regions (**b**). The average distance of the centroids with respect to the geometric center of the regions is also bigger than the one showed in the previous tests (Figure 12). Moreover, the coefficient of variation of the distance is widely increased, reaching 4.2% in the 64 regions configuration. From the color point of view, the effect of this artifact is also noticeable in the increase of the variation on the three channels (Figure 13). Being the value of the green channel 148, the coefficient of variation is 61.4, representing 41.5% of the actual value. This implies the concentrated illumination of the spot light creates huge color differences between the over lighted areas and the shadowed ones. The second artifact consisted on using the same spot light but introducing a more centered distortion in order to check the impact of the residual light around this area in the final result and the importance of the light artifact location with respect to the results obtained. As it can be seen in Figure 11c, the visual result is very similar to the previous one, with many small regions concentrated in the spot light, and bigger areas in the rest of the image. The behavior of the centroid correspondence is also very similar (Figure 12). The statistical results do not show either significant differences, showing a coefficient of variation of the region areas between 43% for 64 regions and 46.5% in the 1024 configuration. The same happens with the color and the centroid distance (Figures 12 and 13). Thus, the difference introduced by displacing the spot light is not relevant as it creates the same artifact in a different point of the cyclorama, not affecting the global results of the calibration process. The third distortion consisted on using only two extern and very diffuse actor lights to create a slightly over-lighted area in the center of the image. The resulting images are very similar to those of the original time-affected configuration, with a central over lighted area (especially in the top of the cyclorama) and shadows in both sides (Figure 11d).