# Optimization of Image Capture Distance for Facial Thermograms in Dentistry
## 2 Materials and Methods
### Thermography Procedure and the Thermograms
#### 2.3.2 Imaging Procedure  
Participant Positioning  
All of the participants' thermograms were taken in a photography room situated in the ABS. The images were shot with the participant seated on a fixed chair in front of a black background, seated at a distance of 4 cm from the black background (back of the chair). The temperature (\({}^{\circ}\)C) and relative humidity (%) of the photo room were measured at each session for each participant using a digital hygrometer (Model No. E0119 TH, Intertronic Hygrometer Thermo, Interdiscount AG, Jegenstorf, Switzerland). These measurements were inserted in the object parameter settings of the software during image analysis. All personal effects including jewelry, glasses, masks, hearing aids, scarves, hair clips, or similar items were asked to be removed (when possible) before the imaging. The participant was instructed to remain calm and sit on the chair for 3 min before the thermographic pictures were taken. The participants were asked to look straight at eye-level with their chin parallel to the floor. Prior to the imaging, the participants' temperatures were measured using an ear thermometer (Braun Thermoscan, Kaz Europe Sarl, Lausanne, Switzerland).  
Camera Positioning  
A mobile phone with the attached thermography camera was fixed on a tripod for image capture. The tripod could be adjusted for height and comprised a swived arm that could be adjusted to set the camera distance from the subject.  
Image Views  
Three views were captured for each participant: frontal, left profile, and right profile. Each of the views were shot at a distance of 15 cm, 30 cm, and 50 cm (Figures 1-3).  
Each view at each distance was repeated five times for each participant. Therefore, a total of 45 images were taken for each participant, and a total of 1350 thermal images were taken for the 30 participants.  
Figure 1: Thermograms taken at a 15 cm distance (right profile, front, left profile).  
Figure 3: Thermograms taken at a 50 cm distance (right profile, front, left profile).  
Figure 2: Thermograms taken at a 30 cm distance (right profile, front, left profile).  
Composing the Frame  
To ensure that all the images were standardized and captured in the exact same manner, the subject was composed in the camera frame using the following criteria:  
* Frontal view: the nose was placed in the center of the frame (Figure 4);
* Profile images (15 cm and 30 cm): the tip of the nose was positioned at the border of the frame with the ears maintained at the middle of the picture (Figure 4);
* Profile image (50 cm): the ears were positioned at the center of the image (Figure 5).  
No magnification was applied during the imaging process for any of the images and views.  
Object Parameters  
Emissivity was set to 0.98, with the reflected temperature set at 22 \({}^{\circ}\)C and atmospheric temperature of 21.4 \({}^{\circ}\)C. The relative humidity percentage during the imaging sessions was 27.0%. The external optics temperature and external optics transmission were fixed at 25 \({}^{\circ}\)C and 0.800, respectively. The distances of the captures were fixed at 0.15 m, 0.30 m, and 0.50 m, as per the study protocol.  
Figure 4: Head positioning at a 15 cm and 30 cm distance.  
Figure 5: Head positioning for profile images at a 50 cm distance.