Citation: | Chen Chentao, Pan Zhiwei, Shen Huiliang, et al. Image stitching and partitioning algorithms for infrared thermal human-body images[J]. Opto-Electronic Engineering, 2019, 46(9): 180689. doi: 10.12086/oee.2019.180689 |
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Overview: Body temperature in medicine is a parameter indicating abnormal activity of human tissues. Over the past few decades, the thermal infrared image of human has attracted extensive interest because it directly reflects the temperature distribution of the human body surface. Based on in-depth analysis, the infrared image can be used to diagnose specific pathologies. In order to carry out thermal infrared image analysis, we need to obtain a complete human body image and perform the correct segmentation of human body parts.
However, efficient algorithms for image stitching and partition of the infrared image are facing challenges and it is worthwhile devoting much effort to this. As can be seen in the picture above, the temperature distribution of the human body in the infrared image is not uniform, the background temperature varies from top to bottom. In addition, the upper and lower body infrared images are not collected at the same time. Thus, the arms may not be in the same position. In the literature, there are three kinds of algorithms for image registration, i.e., feature-based, intensity-based, and transform-based. As infrared thermal human-body images are of limited resolution, low contrast, and barely noticeable texture, the traditional feature-based algorithm cannot work properly. As the position of the arm may be inconsistent, phase correlation algorithm may cause a large error. Among them, intensity-based algorithm is a preferable method, but some existing problems still need to be solved. On the other part, human feature point extraction algorithms mainly include line-by-line scanning and chain-code-based methods, etc., but they are susceptible to noise.
In an effort to overcome these challenges, we proposed two image processing algorithms. First, a template matching algorithm, which uses both binary and grayscale images, is proposed for image stitching. Second, the extreme point detection algorithm is employed to detect the key points. In the image stitching stage, first of all, we solved an accurate binary image for template matching. Based on the idea of Otsu algorithm, our method performs local threshold segmentation on infrared images by using a horizontal sliding window. Next, the starting line of the overlapping region is determined by the template matching with binarization images. The horizontal offset between the upper and lower body images is eliminated by the template matching with grayscale images. The arm area is registered by point matching in the binary image. Finally, the whole-body image is obtained by image fusion. In the image partitioning stage, the key points of the part area are determined by the extremum-point analysis of the human contour. The human body is then partitioned into regions including head, trunk, limbs, etc. Furthermore, the hand area of the human body is separated by a morphological operation. The separation of the foot area is performed similarly.
Experiments show that the proposed preprocessing algorithms produce satisfactory results in image-stitching and portioning. They can effectively support the quantitative and qualitative analysis of human body temperature distribution, which in turn provide intelligent diagnosis assistance for medical treatment.
Infrared imaging system and human-body infrared image. (a) Cabin and workbench; (b) Grayscale and pseudo-color images of upper body; (c) Grayscale and pseudo-color images of lower body
Our infrared thermal image processing framework
Template matching results. (a) Upper body image and search area; (b) Lower body image and template area; (c) Overlapping area
Template matching process. (a) Upper and lower body images; (b) Binary template matching; (c) Grayscale template matching; (d) Image stitching results; (e) Image fusion results
Process of whole body image segmentation. (a) Original image; (b) Detected feature points using ref.[9]; (c) Binary map and key points; (d) Area partitioning results
Curve analysis for searching the upper-body key points. (a) Schematic diagram of the boundary-scan from the central axis of the binary map; (b) Distance map from the central axis to the boundary; (c) Distance gradient from the central axis to the boundary
Schematic diagram of the hand partitioning process and the final result
Image stitching and partitioning results
Regional temperature statistics of a male human body
Regional temperature statistics of a female human body