Moving image modulation transfer function measuring method based on gray threshold segmentation algorithm

Abstract

The invention discloses a moving image modulation transfer function measuring method based on a gray threshold segmentation algorithm, belonging to the field of optical property measurement. The method comprises the following steps of: firstly, switching off a point light source, forming an image by an image sensor, and taking the maximum value of each pixel grey value in the recorded image as a threshold; then, lighting and moving the point light source, forming an image by the image sensor once again to obtain an intensity point expansion function image, and correcting the point expansion function image by using a gray threshold segmentation algorithm; and finally, obtaining a two-dimensional motion dynamic target modulation transfer function through two-dimensional Fourier transform and impression taking. When the point light source does a one-dimensional motion, an intensity line expansion function can be extracted from the intensity point expansion function, and a one-dimensional motion moving image modulation transfer function is obtained through utilizing one-dimensional Fourier transform and impression taking. The method not only can eliminate background light and the dark current of the image sensor, but also can eliminate random noise, and simultaneously gives considerations to the one-dimensional moving state and the two-dimensional moving state. The measurement step is simple.

Description

technical field [0001] The invention relates to a measurement method of a modulation transfer function in the field of optical property testing, in particular to a measurement method of a moving image modulation transfer function. Background technique [0002] The moving image modulation transfer function is an important parameter to quantitatively describe the degree of image quality degradation caused by the movement of the target during the imaging process of the time-lapse imaging system for the dynamic target. Measuring the moving image modulation transfer function and obtaining the transfer function curve can not only obtain the degree of image quality degradation, but also analyze the cause of image quality degradation, and provide a theoretical basis for motion blurred image restoration. [0003] In 1992, SPIE Volume 1971 "Real-Time Numerical Calculation of Optical Transfer Function for Image Motion and Vibration. Part 1: Experiment Verification" introduced a point l...

AI Technical Summary

Problems solved by technology

This method considers that the size of the point light source is negligible, and by selecting a small interval, the dark current of the image sensor outside the interval, background light and random noise can be filtered out, but its disadvantages are: ① It does not take into account The influence of lens diffraction and aberration on the measurement results of the moving image modulation transfer function during the imaging process; ② does not take into account the dark current of the image sensor, background light and random noise superimposed on the point light source image within the selected interval range Influence on the measurement results of the moving image modulation transfer function

This invention patent comprehensively considers the influence of optical system diffraction, aberration, image sensor dark current, and background light on the measurement results of the moving image modulation transfer function, and adopts the method of dividing the initial dynamic target modulation transfer function by the initial static target modulation transfer function , so to a certain extent, the influence of diffraction and aberration of the optical system on the measurement results of the moving image modulation transfer function during the imaging process is filtered out; due to the correction method adopted by the invention: the initial dynamic target modulation transfer function is divided by the initial static target The modulation transfer function is a correction method for the entire image, not a part of the image, so the second problem in the article will not appear: within a certain area, the dark current of the image sensor and the background light will be Superimposed into the image of the point light source, it will affect the final measurement result of the MTF of the moving image

However, this method also has its disadvantages: ① This method does not take into account the influence of random noise on the measurement results of the MTF, so the measurement results of the MTF finally appear as glitches;

[0005] ② This method finally uses the line spread function to obtain the moving image modulation transfer function, so this method is only applicable to the modulation transfer function measurement of one-dimensional dynamic targets, not suitable for two-dimensional dynamic targets

Since this method ultimately adopts the form of dividing the initial dynamic target MTF by the static target MTF, it can also aim at the first problem in the article in the background technology to filter out the effects of diffraction and aberration of the optical system during the imaging process. The influence of the measurement results of the dynamic image modulation transfer function; and because the invention patent adopts the method of synthesizing the static image and the synthetic dynamic image separately from the interference image, it can also filter out the dark current of the image sensor and the second problem in the article. The influence of background light on the measurement results of the dynamic image modulation transfer function; more importantly, the invention uses the threshold segmentation method to further correct the image, and obtains the corrected static target line spread function and the corrected dynamic target line spread function. The second problem and the random noise problem in the first problem in the first patent in the background technology filter out the influence of random noise on the dynamic image modulation transfer function, so that the final measurement curve is smooth, although this measurement method can obtain a lot Good measurement results, but the disadvantages of this method are: ① There are many steps, a total of twelve steps are required, including three image acquisitions, four corrected image calculations for the influence of image sensor dark current, background light and random noise, and five Mathematical operations for the measurement of moving image modulation transfer function; ②This method still uses the line spread function to obtain moving image modulation transfer function, so this method is only applicable to the measurement of one-dimensional moving image modulation transfer function

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