External Thermal Camera Exposure Control Workaround for Low-Cost Security Thermal Cameras

Abstract

Thermal cameras have an advantage in feature extraction, namely the ability to show only objects with/according to temperature; for example, a person with a higher temperature than the immediate surroundings could be extracted from the background with simple machine vision techniques. The problem with industrial thermal cameras for security use is that they are very expensive. A solution would be to obtain less expensive security thermal cameras. However, a problem inherent to these cameras is their automatic self-calibration system. This is problematic in fixed constant comparator programs. This paper proposes a calibration system to regulate the optimal exposure parameter for the analysis of a single, possibly under- or over-exposed image. This calibration system provides an optimal exposure reference for the camera, based on image clarity and reduced image noise. The phenomenon of image noise is caused by under- or over-exposed images. To estimate the exposure quality in the presence of saturated and unsaturated pixels, a temperature-controlled surface is introduced into the camera's field of view. The camera's calibrating point is aimed at this surface; therefore, this is a reference temperature for the camera. Experimental results are presented comparing different reference temperatures to target visibility. The experiment was conducted in a controlled environment.