Automatic focusing method for lensless digital holographic imaging

Abstract

The invention provides an automatic focusing method for lensless digital holographic imaging, and the method comprises the steps: carrying out back propagation on a holographic image, and obtaining a holographic reconstruction image; taking guide filtering as a blurred image function, and calculating a direction information difference value between the reconstructed image and the blurred image by adopting a gradient vector square function to obtain an evaluation function of the holographic reconstructed image; and combining a golden section search method with an evaluation function, determining an optimal defocusing amount, and obtaining an optimal reconstructed image. According to the method, a reconstructed holographic image is blurred by adopting a guide filter, and information of the reconstructed image and information of a blurred image in different directions are extracted respectively. The optimal defocusing amount is determined by comparing the change conditions of the direction information of the reconstructed image and the blurred reconstructed image, the smaller the direction information difference is, the clearer the image is, and otherwise, the more the diffraction fringes are. According to the method, image filtering and edge extraction are combined, interference of diffraction fringes on a target object is eliminated, and an evaluation function can accurately calculate a correct focusing position.

Description

technical field [0001] The invention relates to the technical field of lensless digital holographic imaging, in particular, to an automatic focusing method for lensless digital holographic imaging. Background technique [0002] Lensless holographic imaging uses a photoelectric conversion device (CCD or CMOS) to record the hologram of the measured object, and transmits the digitized hologram to the computer to achieve fast and accurate recording of the hologram. In a lensless digital holographic imaging system, the distance between the plane of the object and the imaging plane of the CCD is called the defocus amount, which cannot be known in advance. However, in the digital holographic reconstruction algorithm, it is necessary to provide the optimal defocus amount to obtain a clear reconstructed image. Therefore, in order to obtain the optimal defocus amount, a variety of autofocus methods have been proposed. [0003] The current autofocus methods are mainly divided into tw...

AI Technical Summary

Problems solved by technology

This method provides a new automatic focusing method based on image edge information. It calculates the sharpness of real and imaginary parts of each focus depth in the same image. The calculation is complicated and the evaluation function curve is not smooth. It is necessary to traverse to find each evaluation function. The value looks for the most value point, so the autom

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