卷积法和角谱法再现显微全息图时补零数的研究

Zero-Padding Number of Convolution Approach and Angular Spectrum for Reconstructing Microscopic Hologram

针对全息图补零法的补零数对再现像和系统效率的影响,结合数字全息显微术中卷积法和角谱法数字再现的原理和再现面与物体放大像尺寸的关系,研究补零数对再现像和系统效率的影响,并采用梯度法来评价再现像的质量。对全息图采用频率滤波提取实像或共轭像的频谱,再采用卷积法或角谱法数字再现,获得物体的放大像。结合再现像的质量和效率两方面因素,提出了补零数的选取依据,即以再现面的物理尺寸不小于物体的放大像时的最小补零数作为最佳补零数,此时能以最小的计算量获得最高质量的再现像。通过实验验证,结果与理论分析一致,证明了选取补零数的依据。

The influence of zero-padding number in zero-padding hologram on reconstructed image and system efficiency is analyzed by combining angular spectrum in digital holographic microscopy with the size relation between magnified image and reconstructed plane. The gradient method is used to evaluate the quality of reconstructed image. The frequency of real image or virtual image is obtained by frequency filter. The object magnified image is obtained by convolution approach or angular spectrum. The evidence of choosing zero padding number is proposed according to the quality of reconstructed image and system efficiency. The experimental results are consistent with theoretical analysis. It demonstrates that the smallest zero-padding number ensuring the size of reconstructed image larger than the magnified image is the best one, at that time the highest quality of reconstructed image is achieved with smallest calculating task.