Evaluation of simplified ROI definition in facial thermography for psychophysiological and medical applications

Stanić, Valentina (author), Geršak, Gregor (author)

Consistent definition of facial regions of interest (ROIs) is essential for comparable evaluation of temperature dynamics, yet manual ROI annotation remains common. As anatomically faithful annotation is time-consuming and cognitively demanding, this study investigates whether simplified geometric ROIs anchored to facial landmarks can be used without introducing differences in temperature statistics that exceed relevant measurement uncertainty levels. Three novice raters annotated five common facial ROIs across repeated sessions. Temperature metrics (mean, median, and standard deviation) were calculated from all pixels and from the warmest 10% of pixels at three spatial resolutions. Differences between annotation approaches were evaluated with respect to the best achievable and realistic uncertainty levels, 0.3 °C and 1.3 °C, respectively. The simplification reduced annotation time by 42% while maintaining excellent inter- and intra-rater reliability. For most ROIs and metrics, differences remained within the stricter uncertainty level, with larger deviations observed mainly in the anatomically variable periorbital region. Lower spatial resolution increased variability, particularly for small ROIs that fell below the minimum size criterion. These results demonstrate that simplified ROI definitions provide comparable temperature statistics while substantially improving time efficiency, supporting their use in manual and automated facial thermography analysis.

• Language: English
• Keywords: infrared thermography, region of interest, facial thermography, thermal image analysis, ROI definition, measurement uncertainty
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FE - Faculty of Electrical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 12 str.
• Numbering: Vol. 16, issue 10, art. 4631
• PID: 20.500.12556/RUL-182421
• UDC: 621.317:159.91:61
• ISSN on article: 2076-3417
• DOI: 10.3390/app16104631
• COBISS.SI-ID: 277685763
• Publication date in RUL: 11.05.2026

Record is a part of a journal

• Title: Applied sciences
• Shortened title: Appl. sci.
• Publisher: MDPI
• ISSN: 2076-3417
• COBISS.SI-ID: 522979353

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: infrardeča termovizija, območje zanimanja, obrazna termografija, analiza termogramov, definicija ROI, merilna negotovost

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0225
• Name: Metrologija in kakovost