Non-Invasive Forehead Segmentation in Thermographic Imaging

Abstract

The temperature of the forehead is known to be highly correlated with the internal body temperature. This area is widely used in thermal comfort systems, lie-detection systems, etc. However, there is a lack of tools to achieve the segmentation of the forehead using thermographic images and non-intrusive methods. In fact, this is usually segmented manually. This work proposes a simple and novel method to segment the forehead region and to extract the average temperature from this area solving this lack of non-user interaction tools. Our method is invariant to the position of the face, and other different morphologies even with the presence of external objects. The results provide an accuracy of 90% compared to the manual segmentation using the coefficient of Jaccard as a metric of similitude. Moreover, due to the simplicity of the proposed method, it can work with real-time constraints at 83 frames per second in embedded systems with low computational resources. Finally, a new dataset of thermal face images is presented, which includes some features which are difficult to find in other sets, such as glasses, beards, moustaches, breathing masks, and different neck rotations and flexions.

Keywords: body parameters; computer vision; forehead segmentation; image processing; thermographic imaging.

Figure 1

Different steps of the proposed method. (a) Grayscale image; (b) Thresholded image; (c) Binary mask; (d) Vector directors and main points to extract forehead region; (e) Ellipse calculation; (f) Eyes detection; (g) Forehead region overlapped with grayscale image.

Figure 2

Result of the proposed method for users (a), (b), (c), and (d). Where grayscale image, detected ellipse with its angle of rotation, transformed ellipse, detected region of forehead, ground truth of the forehead and the difference between ground truth and proposed segmentation are shown by rows.