Zoom Lens Calibration for Microscopic based Augmented Reality

Abstract

The augmented reality (AR) guidance system have been developed for image guided intervention, very intuitive and states of art technique in the surgical navigation. The microscope is preferred equipment in ENT surgery, thus we tried to apply the AR system into microscope. To use the AR in the microscope, the intrinsic parameters and hand-eye parameters should be obtained, which are essential parameters to calculate the position and orientation of microscope from the patient. Particularly, those parameters are changed according to variation of the magnification levels. Moreover, it is hard to predict the variation of those parameters due to nonlinearity of zoom lens. Therefore, we developed photogrammetric feedback system to find camera parameters accurately during a surgery. In the proposed system, camera calibration and hand-eye calibration are only performed in the low magnification level. It did not use parameter table, thus there is no need to calibrate a camera in other magnification levels. In this system, several images of calibration board are required to estimate the camera parameters when the magnification level is changed. The proposed photogrammetric feedback technique was used to find the intrinsic and hand-eye parameters in certain magnification level from the images and initial parameters which are taken from the lowest magnification level. Through the experiments, performance of the proposed technique were tested, the results showed sufficient stability and accuracy. Particularly, the proposed system are suitable to the microscope that is hard to use the inner encoder system. ⓒ 2014 DGIST