Monocular Range Estimation through a Double-Sided Half-Mirror Plate

This paper proposes a novel single-camera range estimation method using images transmitted through a double-sided half-mirror plate. The exit-side halfmirror reflects and transmits the transmitted light through the incident-side half-mirror. The transmitted light directly reaches to the camera through the exit-side half-mirror, but some of the reflected light at the exitside half-mirror is then reflected again at the incidentside half-mirror and reaches the camera. Those multiple paths create a layered image in which displacement between the images differs with object distance. The constraint in the layered image is presented. The range to the object can be derived by finding correspondences on constraint lines using the autocorrelation of the layered image with similarity indices. The correspondence position is estimated using a parabola fitting with systematic error cancellation to enhance the accuracy without iteration. Ray tracing enables computation of a rigorous range to the object. This paper presents a theoretical formulation and experimental results obtained using an actual system with a doublesided half-mirror, which is realized using a transparent acrylic plate and two half-mirrors on thin glass-plate.