## 4 Tests  
To prove the validity of the proposed calibration process, two sets of tests were performed. The first one focused on correcting the actual light conditions of a virtual TV set using our workflow (with an expert validating the results) and the second consisted on altering the lighting conditions of a virtual TV set cyclorama to observe the results using known artifacts and creating a set of example cases to illustrate the user manual for nonexerts. Both sets of tests focused in proving the effectiveness of the visual analysis of the different generated images as well as the correspondence between these  
Figure 7: Correctly illuminated cyclorama subdivided in 1024 regions. All the regions have a similar size and the centroids tend to be located in their geometric center (**a**). Image subdivided in 256 regions. In the “1” area, which is over-lighted the regions are smaller than in the “2” area, which is shadowed (**b**). Image subdivided in 256 regions. In the “1” area, which is over-lighted, each ideal centroid has two or more real centroid correspondences. In the “2” area, which is shadowed, there are several ideal centroids which have no real correspondent (**c**). visual results and the statistical data obtained. Among all the statistical data obtained, we focused in the standard deviation of the area (number of pixels) of the regions. As all the regions should have a very similar area, the standard deviation should tend to cero. In order to facilitate the understanding of the magnitude, we used the coefficient of variation expressed as a percentage to interpret the results. The process was applied dividing the images in 64, 128, 256, 512 and 1024 regions in order to compare the results and verify if the number of divisions had any impact in analysis. The study was developed in a virtual TV set at the Faculty of Communication Sciences of the University of Santiago de Compostela (Spain). The set has a green cyclorama of 5.10 m wide by 3.3-m long and 3-m high surrounding a manually illuminated acting area. At the beginning of the test process the cyclorama lighting presented several visible artifacts due to time and usage since their last calibration. As it has been previously mentioned, the first set of tests focused on correcting these artifacts. The first iteration of the calibration process was performed in order to check the original state of the illumination. After applying the first two steps a set of images for each number of subdivisions was obtained (Figure 8a). In this image the difference between areas is noticeable being the ones in both sides slightly bigger than the ones in the center (Figure 8a left). This empirical information is confirmed by Figure 8a right in which the correspondence of the centroids is represented. In the top and center of the image there is an accumulation of centroids while in the sides their number decreases. With these two elements we can empirically conclude that there is too much light in the center and top of the cyclorama and there are shadows in both sides. In Figure 9, the number of ideal centroids with 0, 1, 2 or more than two correspondent real centroids are represented. The number of centroids with 0 correspondences is around 10% in all cases, being superior in the 512 and 1024 regions configuration. Figure 8: Images of the three steps process of correcting the cyclorama illumination: original configuration (**a**), first correction (**b**) and second correction (**c**). The images represent the 512 regions subdivision (**left**) and the centroid correspondence (**right**). From a statistical point of view, the coefficient of variation of the size of the regions goes from 25.5% when the image is divided in 64 regions to 27.6% for the 1024 subdivision (Figure 10). This means that the variation of the size of the regions with respect to the average area (which corresponds to the ideal area size) is, in average, between these two values.