基于现场可编程门阵列的图像调焦系统

Image auto-focusing system based on field programmable gate array

数字图像自动调焦技术,不仅能提高调焦精度,而且能降低对成像系统加工和装配精度的要求。采用基于功率谱的评价函数对成像系统的聚焦位置进行识别,提出了基于现场可编程门阵列(FPGA)的自动调焦系统实现方案,主要完成图像预处理、清晰度判别和对焦控制等功能。针对自动调焦算法计算量大、计算复杂等特点,采用中值滤波和灰度值线性变换的图像预处理方法,以及流水线作业、"乒乓"操作、双蝶形处理器复用、基-2 FFT算法相结合的工作模式。研究表明,利用FPGA强大的并行及高速数据处理能力,使得图像调焦算法不再成为复杂控制系统的速度瓶颈。

The digital image auto-focusing technology can not only improve focusing precision but also decrease the accuracy demand in machining and assembling imaging systems. The evaluation function based on power spectrum is used to recognize the focus positions of imaging systems and the realization scheme of the auto-focusing system based on field programmable gate array （FPGA） is put forward. It mainly accomplishes image pretreatment, definition evaluation and auto-focus control and so on. Aiming at the enormous computation and high complexity of the auto-focusing algorithm, the preprocessing method of combining the median filter with the linear transform of gray value, the pipelining structure, the ＇ping-pong＇ working mode, the sharing processor of double butterfly shape and the base-2 FFT algorithm are presented. The research indicates that the actualization of the auto-focusing algorithm based on digital image processing becomes the speed bottle-neck of complex control systems no longer by using the strong parallel and high speed processing capacity of the FPGA chip.