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自动聚焦是数字全息技术中实现自动重建的关键技术之一,而自动聚焦的关键是寻找性能可靠的聚焦评价函数。通过对现有聚焦评价函数的深入研究分析,及对图像清晰度相关理论的学习,面向海洋生物全息图提出了一种新的聚焦评价函数,该聚焦评价函数的依据是局部标准差分布能够反映图像细节信息的特性及标准差自身具有较高稳健性的特征,以标准差作为离散程度度量,将全息图重建像细节的离散程度作为其清晰度指标,并将清晰度最大值对应的重建距离作为最佳重建距离,以此完成自动聚焦。实验结果表明:与其他聚焦评价函数相比,该方法具有较好的单峰性、较高的灵敏度和信噪比(SNR)及较好的无偏性等性能,且对于海洋生物全息图具有较强的实用性和通用性。因此,该方法可以满足海洋生物全息图自动重建的需求。
Autofocusing is one of the key technologies for automatic reconstruction in digital holography, and the key to autofocusing is to find a reliable focusing evaluation function. Through the further research and analysis of the existing focusing evaluation function and the study of the related theories of image sharpness, a new focusing evaluation function is proposed for the marine biological hologram. The focusing evaluation function is based on that the local standard deviation distribution can reflect The characteristic and standard deviation of the image detail information have their own characteristics of high robustness. Taking the standard deviation as the measure of the degree of dispersion, the degree of detail of the reconstructed image is taken as the definition index, and the reconstruction distance corresponding to the maximum value of the sharpness As the best reconstruction distance, in order to complete the auto-focus. The experimental results show that this method has better performance of unimodal, higher sensitivity and signal-to-noise ratio (SNR) and better unbiased performance compared with other focusing evaluation functions, and has the following advantages Strong practicality and versatility. Therefore, this method can meet the needs of automatic reconstruction of marine biological holograms.