# Oral and Dental Spectral Image Database--ODSI-DB
## 2 Materials and Methods  
The optical imaging system built for dental and oral imaging consisted of a spectral camera, a ring illuminator (FRI61F50, Thorlabs Inc., Newton, NJ, USA), a halogen light source (Thorlabs OSL2, Thorlabs Inc., Newton, NJ, USA) with an extended IR-range light bulb (OSL2 BIR, Thorlabs Inc., Newton, NJ, USA), and a chin-forehead rest, all mounted on a platform, making the system mobile, see Figure 2.  
Initially, the spectral camera chosen was the Nuance EX (CRI, PerkinElmer, Inc., Waltham, MA, USA). The camera allows imaging at 1392 \(\times\) 1040 pixel spatial resolution and has spectral resolution in the range 450-950 nm with 10 nm bands (51 bands in total). The Nuance EX spectral camera was subsequently replaced with Specim IQ (Specim, Spectral Imaging Ltd., Oulu, Finland). The Specim IQ spectral camera has a lower spatial resolution (512 \(\times\) 512 pixels), but the spectral resolution has an increased range of 400-1000 nm with approximately 3-nm steps (204 bands in total). Both spectral cameras have 12-bit sensors. Switching the camera simplified the imaging significantly: Nuance EX camera requires two runs per one imaging, once to determine optimal integration times for the spectral bands and a second run to perform the actual image capture. Specim IQ is a line-scanning camera with a constant integration time over the band images. The chin-forehead rest was used to reduce the involuntary head movements during imaging and was connected to the main platform of the optical setup. The ring illuminator and the camera were mounted on another platform that was allowed to freely slide over the main platform to allow optimal imaging geometry in relation to the test subject. For image normalization purposes (see below), we imaged a reference sample with a known reflectance spectrum during the imaging process. The reference sample used was a matt diffuse gray ceramic sample (\"Matt Diff Grey\", Ceram Research, Ltd., Lucideon, Ltd., Stoke-on-Trent, UK) instead of a white plate. White references were found to give over-saturated responses, while the corresponding sample remained under-exposed. The Institute of Dentistry of University of Eastern Finland (UEF) recruited the test subjects at the UEF's Dental School Clinic (Kuopio, Finland) and the UEF's School of Computing recruited test subjects in Joensuu, Finland. Ethical permission for the research was granted by The Hospital District of Northern Savo, Kuopio, Finland (413/2016). The volunteering test subjects were fully informed about the research and gave their written consent prior to spectral imaging. A total of 30 test subjects were recruited for the spectral imaging. Figure 2: Imaging system with (**a**) Nuance EX, and (**b**) Specim IQ spectral cameras. The spectral imaging process started with imaging the facial skin around the mouth area (Figure 3a), followed by imaging a gray reference tile positioned at approximately at the same location as the face, thus retaining the imaging geometry. Next, the system is moved closer to the patient and dental imaging is performed: the front teeth are imaged bitten together (Figure 3b), the lower and upper teeth's occlusal surfaces (Figure 3c,d) are imaged most of the time by using a dental mirror or lip retractors. The dental mirror posed a compositional challenge: there was little time to pose the scene optimally as the mirror fogs quickly when the patient needs to breath. A dental expert handled the patient, and the dental mirror, and helped to expose the areas of interest for spectral imaging. If the patient had other features of interest (such as infection sites or pigmentation changes), they were imaged also. The gray reference sample was imaged as needed anytime the imaging geometry changed significantly. When Nuance EX was used, the reference and dark-current images had to be measured every time the integration times were recalculated. Specim IQ saved dark-current images automatically during a spectral image capture.