# Applications of Capacitive Imaging in Human Skin Texture and Hair Analysis
## 3 Results  
In this section, three experiments are conducted to examine the performance of the presented algorithms on capacitive images. The first experiment evaluates [PERSON] and [PERSON] segmentation algorithm to automatically count the skin polygons, i.e., the skin areas shaped between wrinkles. For this purpose, capacitive images were recorded from 12 volunteers aging from 12 to 74 years old. The samples were taken from the middle polar forearm area while the arm was in resting position to reduce strain. Then, the segmentation algorithm was applied using Epsilon E100 software and the average number of polygons per square millimeter was correlated against the subjects' age. The results in Table 1 demonstrate that the average number of polygons per surface area decreases with age. The calculated correlation (\(-0.71\)) comes in agreement with previous studies in the literature [10; 11]. The second experiment consists of a short comparison between C-Cube, a calibrated digital spectroscope (Pixience, Toulouse, France) [37], and Epsilon E100 in feature length estimation. The same skin area of polar forearm was captured with both instruments and three furrows were randomly selected (Figure 7). C-Cube software provides the length measurement as a default feature by drawing the linear segment of interest on the captured frame (Figure 7 left). Epsilon E100 does not provide such feature, so the region of interest was cropped, and our length estimation algorithm was applied (Figure 7 right). The results in Table 2 suggest that if there are no neighboring artifacts in capacitive images, such systems can calculate the length of a fur \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline
**Age** & 12 & 16 & 26 & 28 & 31 & 48 & 48 & 50 & 60 & 64 & 74 & \(R^{2}\) & \(p\)-Value \\ \hline
**Polygons/mm\({}^{2}\)** & 12.1 & 10.7 & 11.6 & 10.9 & 10.3 & 10.4 & 8.8 & 7.9 & 8.0 & 7.7 & 6.0 & 8.8 & \(-0.71\) & \(<\)0.0006 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental results for skin polygons per surface area in middle polar forearm across 12 volunteers in different age groups using capacitive images. The correlation of the average number of polygons per mm\({}^{2}\) against subjects age is calculated to \(-0.71\). Reproduced with permission from [33], John Wiley and Sons, 2018. Figure 6: Example of threshold application on hair capacitive image. On the left the original frame, where acclimatized hair on bright green and air/bad contact on darker green shades. Right, the software output after a range threshold is applied to exclude pixels with bad contact before calculating water content. In the final experiment, the ability of capacitive imaging sensors to measure hair water content and desorption rate are examined. For this purpose, scalp hair samples from three volunteers were washed in deionized water and dried before left to acclimatze overnight in three different humidity chambers. Saturated salt solutions adjusted the relative humidity levels while both temperature and relative humidity were logged every 10 s using SHT35 by Sensirion [38]. The selected salts are potassium nitrate (85% RH), sodium chloride (75% RH) and magnesium nitrate (67% RH). After acclimatization, the samples were moved in 21 \({}^{\circ}\)C & 35% RH conditions, side by side, and they were held against the sensor surface with a plastic plug provided by the manufacturer. The system was capturing video frames until the water loss rates reached a flat state or until the video exceeded 5.5 h. In order to target only the pixels in contact with hair, a range filter from 3.5 to 80 was applied on each frame. The selection of these limits is based on previous work with Epsilon E100 [39]. Five video instances from the same hair sample per acclimatization chamber are shown in Figure 8.  
Two observations are made from the experimental results in Figure 9 and their summary in Table 3. First, the hair water content right after acclimatization correlates well with the relative humidity of the chamber.