使用立體視覺系統估測眼鏡之姿態

由於眼鏡會折射光線，導致由眼鏡外向觀測到的眼睛影像失真，而難以還原被折射的視線，因此目前的視線追蹤技術大多只適用於無須配戴視力矯正眼鏡的使用者。為解決透過眼鏡估測視線的問題，必須先估測眼鏡的方位。在本論文中我們發展了一套使用立體視覺系統來估測眼鏡方位的方法。為了協助眼鏡的定位，我們在鏡框四角貼上四個足標點。而為了建立眼鏡的光軸與前後球面等參數與這四個足標點的關係，我們建構了一套由單軸平移台構成的校正系統。在平移台上我們以 ARTag 為基礎，設計了一個類似西洋棋盤格的校正目標物。其中，每一個黑色的格子都加上一個 ARTag 編碼。這個校正目標物的好處是即使僅取得部份影像，我們也可藉由 ARTag 找出每一個校正點的位置。特別是在眼鏡折射的影響下，這個由 ARTag 構成的校正目標也可以協助我們定出折射後的校正點影像座標。透過光線追跡運算，我們可以估測出鏡片的方位。而由四個足標點的三維位置，即可定義透鏡座標系統。實際實驗顯示，這個眼鏡方位估測方法的位置精確度約在 1 mm 以內，而方位精確度則在 2.5 度左右。可用於修正視線追蹤系統中，眼鏡造成的折射效應。

關鍵字

視線追蹤；眼鏡；折射；立體視覺；光學鏡片； ARTag

並列摘要

Due to optical refraction induced by spectacle lenses, eye images observed from outside of the lens suffer from certain degrees of distortion. The true line-of-sight (LoS) is difficult to be recovered with lens refractions and, hence, the state-of-the-art model-based gaze tracking methods is not applicable to users wearing eyeglasses. In order to tackle this problem, it is essential to know the position and orientation of the spectacle lens. In this work, we develop a lens pose estimation method based on the stereo vision technology. Four fiducial markers are attached to the corners on the eyeglasses frame for assisting eyeglasses localization. Furthermore, to determine the relationship between the fiducial markers and the lens pose (including the position and orientation of the optical axis and the curvatures of the exterior and the interior lens surfaces), we use a translation stage to develop a calibration system. On the translation stage, a checkerboard pattern is used as a calibration target. For allowing us to identify the calibration points, each black square of the checkerboard pattern is replaced with a ARTag. Therefore, even if we only observe partial portion of the calibration pattern, we are still able to determine the image locations of each calibration point. In particular, with the influence of a spectacle lens, the calibration points can be determined easily. With ray tracing technique, we can estimate the lens pose with nonlinear optimization. Then, using the computed 3-D coordinates of the fiducial markers, we can compute a consistent lens coordinate system (LCS). Real experimental results show that the location estimation error and the orientation estimation error are below 1 mm and 2.5 degrees, respectively. A lens pose estimation method with the abovementioned accuracy is sufficient for compensating the influences of spectacle lens refractions in a gaze tracking system.

並列關鍵字

Gaze Tracking ； Eyeglasses ； Refraction ； Stereo Vision ； Optical Lens ； ARTag

參考文獻

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國際替代計量

使用立體視覺系統估測眼鏡之姿態

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