Autofocus method for multi-object digital holographic measurement

Abstract

An autofocus method for multi-object digital holographic measurement relates to the technical field of digital holographic measurement and solves the problem in the prior art that a focus curve obtained by a criterion function has a low peak value and is difficult to distinguish due to the influence of system and environmental noise. The method includes a first step of acquiring a hologram; a second step of separating the hologram; a third step of setting an automatic focus search range and reconstructing an image; a step four of obtaining an autofocus curve; a step five of drawing the Ci curves obtained by all holographic subgraphs in a unified coordinate system by using the set autofocus search range as a abscissa and using the Ci values as an ordinate; and a step 6 of reconstructing theoriginal hologram based on the specific reproduction distance of multiple objects obtained in the step 5, and putting all reconstructed images in a unified spatial coordinate system to obtain a spatial distribution state of the multiple objects. The method obtains an obvious peak at the focus by subjecting the autofocus criterion function to exponential transformation, and reduces the peak discrimination difficulty.

Description

Technical field [0001] The present invention relates to the technical field of digital holographic measurement, in particular to a focusing method for multi-target digital holographic measurement. Background technique [0002] Digital holographic measurement can obtain the amplitude and phase information of the measured object, which is an important measurement method in optical measurement. The photoelectric conversion device (CCD or CMOS) is used to record the hologram of the measured object, and the hologram can be digitally processed to obtain the reproduced distance and reproduced image of the measured object. Therefore, digital holography can realize real-time measurement and positioning of the target surface topography. [0003] The reconstruction process of the hologram reconstruction uses the diffraction integral calculation of the light field propagation to obtain the light field distribution of the reconstructed image, and obtaining an accurate reconstruction distance i...

AI Technical Summary

Problems solved by technology

However, the processing results found that the peak of the focus curve is not obvious, and if the focus range is large, the characteristic peak may be submerged in the noise

[0007] In summary, it can be found that when the criterion function is used to find the target object in the digital hologram, a single object presents a single-peak curve, and the abscissa at the peak is the focus position. In the experiment, due to the influence of system and environmental noise, the criterion function will be obtained The peak value of the focus curve is low and difficult to distinguish

At the same time, when there are multiple targets in the recorded hologram, the peak value on the corresponding curve at each target position is lower, and the noise in the curve will cause some peaks to be submerged and cause the target to fail to focus

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