显微数字全息数值再现中的自动聚焦

自动聚焦是显微数字全息数值再现中的一项关键技术。基于菲涅耳变换重建算法, 采用实验验证的方法, 对显微数字全息成像中六种典型聚焦评价函数的性能进行了对比研究。提出了利用再现像部分区域进行调焦判断的方法。结果表明, 这些函数都具有较好的单峰性、一致的调焦范围和准确性, 但与梯度运算相关的调焦函数运算时间太长; 傅里叶频谱函数调焦速度最快, 是首选的聚焦评价函数。选取再现像部分区域作为调焦计算区域, 可大大缩短调焦时间。对于低信噪比全息图, 利用维纳自适应滤波进行预处理及对再现像进行后处理, 有利于提高自动调焦的准确性及再现像的质量。

Autofocus for Numerical Reconstruction in Digital Holographic Microscopy

Autofocusing is the key of numerical reconstruction in digital holographic microscopy. Based on Fresnel transform algorithm, the performance of six typical autofocusing evaluation functions are studied experimentally. A method which only uses part of the reconstruted image as autofocusing area is proposed to decrease the calculating time. The results show that these functions have better unimodality, same adjusting focus range and accuracy, but the functions related with gradient are too slow to use in the numerical quasi-real time reconstruction. Fourier spectrum function is the optimum one for its minimum calculating time. The adjusting focus time can be decreased greatly by choosing a part of the reconstructed image as calculating area. For low signal-to-noise ratio hologram, the autofocusing accuracy and image quality can be improved by applying Wiener self-adaptive filter.