采用树脂透镜的掌纹图像采集光学系统设计

为了获得高分辨率、高对比度和低畸变的掌纹图像,同时实现系统的轻量化和高性价比,本文基于全反射原理,采用树脂材料设计了一款由6片镜构成双远心光路的掌纹采集光学系统。树脂材料的选用减轻了光学系统的总重量;基于光的全反射原理的系统设计增强了掌纹图像的对比度;选择双远心光学结构,便于对倾斜物面所产生的梯形畸变进行矫正。对所设计光学系统的成像质量分析表明,该系统所有视场的光学传递函数（MTF）在Nyquist频率228 lp/mm处均达0.55以上,畸变〈0.14%。设计的光学系统可以采集120 mm×160 mm的手掌区域,实际手掌面上的分辨率达到500dpi,采集的掌纹图像分辨率达到8.0×106 pixel,满足了实际采集的要求。

Design of optical system based on resin lens for palmprint image sampling

In order to acquire a palmprint sampling image with high resolution,high contrast and low distortion and to achieve system lightweight and high performance-to-price ratio,a double telecentric optical system with 6 resin lenses was designed based on the principle of total reflection.The weight of system has been reduced largely due to resin lenses;and the resolution of acquired image has been enhanced because of the optical design based on the total reflection.Furthermore,the selection of the double telecentric optical system ensures the correction of the trapezoidal distortion introduced by the tilt object surface.It is shown that the Modulation Transfer Function（MTF） of the palmprint image sampling system is higher than 0.55 at Nyquist frequency of 228 lp/mm,and the maximum distortion of the image is less than 0.14%.Moreover,the collection range of system is 120 mm×160 mm within a palm,the actual resolution of palm can reach 500 dots per inch,and the image resolution is 8×106 pixels.These results meet the requirements of palmprint image sampling with high-precision and low distortion.