快速虹膜自動對焦方法

在本論文，我們提出了一個新的虹膜自動對焦方法，只需要在取像設備的鏡頭前加裝一個三角形狀的光圈。由於點光源會在人類角膜上形成一個虛擬影像，大約是與虹膜紋理在同一焦平面上，所以，當虹膜紋理聚焦時，點光源的虛擬影像也會聚焦。一個離焦的點光源的虛擬影像在影像平面上所形成的三角形狀亮點，其亮點的大小和方向可以用來推算聚焦虹膜紋理要移動的步伐量和所需的調整方向。我們在論文中也替未校正的取像設備推導了一梯度下降的自動對焦控制法則。而進一步研究實驗表明，如果梯度下降的自動對焦控制法則的步伐數選擇適當，將可以在自動對焦的過程中只需要一個步伐就能完成自動對焦。本論文的實驗測試了所提出的方法，其結果表明，本論文所提出的方法非常有效且準確。

關鍵字

虹膜辨識；虹膜影像系統；自動對焦；角膜反射；三角形狀光圈

並列摘要

In this thesis, a new iris autofocus method is proposed which requires only to add a triangle entrance aperture in front of the camera lens. Since the virtual image of a point light source (VIPLS) formed behind the human cornea is approximately at the same focal plane of the iris, when the iris pattern is out of focus, the VIPLS is out of focus too. An out-of-focus VIPLS projects a triangle glint area on the image plane. The size and orientation of the glint can be used to estimate how well the iris is focused and to infer the amount and the direction of the focus adjustment, respectively. A gradient-descent control law is developed for uncalibrated motorized lenses. Further study shows that if the step size of the gradient-descent control law is properly selected, the autofocus process can be completed in one step. Real experiments have been conducted to test the proposed method and the results show that it is very efficient and accurate.

並列關鍵字

Iris Recognition ； Iris Imaging System ； Autofocus ； Corneal Reflection ； Triangle Aperture

參考文獻

[1] R. P. Wildes, “Iris recognition: An emerging biometric technology,” Proceedings of the IEEE, vol. 85, no. 9, pp. 1348–1363, 1997.

Google Scholar

[2] H. Borgen, P. Bours, and S. Wolthusen, “Visible-spectrum biometric retina recognition,” Intelligent Information Hiding and Multimedia Signal Processing, pp. 1056–1062, 2008.