Coaxiality Evaluation of Coaxial Imaging System with Concentric Silicon-Glass Hybrid Lens for Thermal and Color Imaging.

Tomoyuki Takahata

doi:10.3390/s20205753

Abstract

Thermal imaging is useful for tasks such as detecting the presence of humans and recognizing surrounding objects in the operation of several types of robots, including service robots and personal mobility robots, which assist humans. Because the number of pixels on a thermal imager is generally smaller than that on a color imager, thermal images are more useful when combined with color images, assuming that the correspondence between points in the images captured by the two sensors is known. In the literature, several types of coaxial imaging systems have been reported that can capture thermal and color images, simultaneously, from the same point of view with the same optical axis. Among them, a coaxial imaging system using a concentric silicon–glass hybrid lens was devised. Long-wavelength infrared and visible light was focused using the hybrid lens. The focused light was subsequently split using a silicon plate. Separate thermal and color images were then captured using thermal and color imagers, respectively. However, a coaxiality evaluation of the hybrid lens has not been shown. This report proposes an implementation and coaxiality evaluation for a compact coaxial imaging system incorporating the hybrid lens. The coaxiality of the system was experimentally demonstrated by estimating the intrinsic and extrinsic parameters of the thermal and color imagers and performing 2D mapping between the thermal images and color images.

Highlights

Thermal images are useful for various purposes, including for detecting the presence of humans by measuring body surface temperatures [1,2] and performing noninvasive measurement in agriculture [2,3,4]
Because the wavelength of long-wavelength infrared (LWIR) light captured by thermal cameras is approximately 10 times longer than that of visible light captured by conventional color cameras, thermal imagers generally have a smaller number of pixels than color imagers
Thermal images can be useful in applications involving 3D mapping of thermal distributions in buildings [5,6] and object surface temperatures [7], combining color and depth information

Summary

Introduction

Thermal images are useful for various purposes, including for detecting the presence of humans by measuring body surface temperatures [1,2] and performing noninvasive measurement in agriculture [2,3,4]. It is difficult to design and manufacture thermal-imaging cameras equipped with imaging sensors that incorporate large numbers of pixels. Thermal images can be useful in applications involving 3D mapping of thermal distributions in buildings [5,6] and object surface temperatures [7], combining color and depth information. Several researchers have reported the detection and tracking of humans using combinations of thermal and color images [8,9,10,11,12,13,14] or depth images [15]

Methods

Discussion

Conclusion