# Oral and Dental Spectral Image Database--ODSI-DB
## 3 Results and Discussion
### Data File Formats  
The relative reflectance spectral images were saved as Tiff image files. The format supports various image types, multi-page datasets and custom tags. Our spectral image Tiffs contain an RGB preview image of the spectral image on the first page, followed by a grayscale band image sequence starting from the second page. For the RGB-render, a CIE D65 light source and CIE 1931 2\({}^{\circ}\) Standard Observer were used. The image data are accompanied by a list of center wavelengths of the spectral bands in a custom tag 65,000, as a list of 32-bit floats. Tag 65,111 contains a free-form ASCII string of metadata. The metadata in our oral and dental spectral image dataset include the camera used,  
Figure 5: Screen capture of the annotation tool.  
the objective lens used, light source and settings, imaging date, and the miscellaneous measurement data, such as the blood pressure and oxygen saturation before and after the imaging. The following pattern is used for all metadata strings:  
Spectral camera: Nuance EX (CRi, Inc., USA).  
Illumination: Thorlabs OSL2 halogen light source (100% power) + Thorlabs Ring Illuminator.  
Objective lens: Samyang 35 mm f/1.4.  
Aperture: f/11.  
Reference sample used: Matt diffuse gray sample (\"Matt Diff Grey\", Ceram Research, Ltd., UK).  
Blood pressure and pulse (before imaging): 165/80, 77 Blood oxygen saturation (before imaging): 95%  
Blood pressure and pulse (after imaging): 164/80, 72 Blood oxygen saturation (after imaging): 97%  
Spectral data: spectral reflectance.  
Note: Values have been scaled to range [0,1] due to flat reference sample.  
Date of spectral image capture: 2018/05/28.  
The filenames of the spectral images are in following format  
group \"_\" set ( \"_\" take | \"_inpainted\"? \"_GDBICP_similarity\"? ) \"_tif\"  
where group is an image grouping number, set is one of face, front, bottom, top, or a specific feature of interest, take is a number for images where the focal point is changed between takes. String inpainted is present in the name when the image has been digitally inpainted, while GDBICP_similarity is present if image registration has been performed. One or both of the two strings are present always and only in spectral images that have been acquired with Nuance EX spectral camera, and never in images acquired with Specim IQ.  
The annotation tool (Figure 5) created for the project creates polygonal markings. These polygons are saved in a semicolon-separated text file. Each line defines an individual marking and follows the format  
Annotation label; R, G, B; X1, Y1; X2, Y2;...; Xn, Yn;  
where R, G, and B are the sRGB color coordinates in 0-255 range, and pixel coordinates \(X_{n}\), \(Y_{n}\) describe the polygon vertices. The coordinate system's origin is at the top-left corner, positive \(X\)-axis leads to the top-right corner, and a positive \(Y\)-axis to the bottom-left corner of a spectral image. Since this text-based annotation format is relatively inconvenient for practical use, the oral and dental spectral image dataset contains annotations as bi-level mask images saved in multi-page Tiff files. The mask labels are stored in tag 65,001 as an ASCII-string on each mask image page. The multi-page Tiff solution was chosen due to the annotation tool allowing for overlapping annotation markings. A single image solution would have necessitated encoding the annotation labels in pixel values, requiring static numeric representations for the labels. Using the Tiff tag to save the label allows free-form strings without fixing labels with numeric values.  
The spectral images and the related annotations have been cropped to ensure the anonymity of the test subjects participating in the research.