An accurate measurement method for the spatial resolution of area array spectral imaging equipment

Chu Songnan; Liu Haitao; Hu Qiqi; Wang Haifeng; Zhang Dayong; Luo Yongquan

doi:10.12086/oee.2019.180458

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Chu Songnan, Liu Haitao, Hu Qiqi, et al. An accurate measurement method for the spatial resolution of area array spectral imaging equipment[J]. Opto-Electronic Engineering, 2019, 46(11): 180458. doi: 10.12086/oee.2019.180458

Citation:

Chu Songnan, Liu Haitao, Hu Qiqi, et al. An accurate measurement method for the spatial resolution of area array spectral imaging equipment[J]. Opto-Electronic Engineering, 2019, 46(11): 180458. doi: 10.12086/oee.2019.180458

An accurate measurement method for the spatial resolution of area array spectral imaging equipment

Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan 621900, China

Fund Project: Supported by National Key R & D Program of China (2017YFC0803806) and National Engineering Laboratory for Forensic Science Open Object Fund (2017NELKFKT04)

More Information

Corresponding author: Luo Yongquan, E-mail: uestcaep@126.com

Received Date 05 September 2018

Revised Date 22 February 2019

Published Date 01 November 2019

Abstract

Abstract

Quantitative methods have been formed to measure the spatial resolution in spectral imaging field, but the results may differ with imaging position change when the resolving power of detector is deficient. Based on the spectral images of black-white lines under accurate shift, a new method for detecting the spatial resolution of area array spectral imaging equipment is proposed. This method presents the curve showing the gray level variation with the displacement of object for a single pixel, and can obtain all the results of gray level distribution among pixels theoretically. Through one type of curve division, the density value of the black-white lines which can be discerned on any imaging position will be obtained. This method has overcome the shortcoming of current methods, and its feasibility is validated by an experiment for one area array spectral imaging equipment.
- spectral imaging /
- spatial resolution /
- accurate measurement

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References

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Overview

Overview

Overview: Spatial resolution is an important performance parameter of digital imaging equipment. At present, the commonly used laboratory measurement method for human eyes is to interpret the image of the spatial resolution testing board. In the field of spectral imaging, a quantitative measurement method of spatial resolution based on data processing has been established. The spectral image of black-white line pair resolution testing board is taken in this method. If the ratio of the adjacent gray peak value and gray valley value (PVR) corresponding to the black-white line pair on the image is larger than $\sqrt 2 $, the line pair can be distinguished. However, when the detector is not capable of resolving the targets, the method has the phenomenon of different measurement results caused by different imaging locations, which will make the results obtained by different experiments difficult to be consistent. In order to solve the above problems, this paper proposes an accurate measurement method for the spatial resolution of the camera of array spectral imaging. By taking a series of spectral images of black-white line pairs under continuous precision displacement, the curve of variation of gray level with displacement of two adjacent pixels in the translation direction is drawn. If the difference in pixel sizes is ignored, the spacing between two curves in the translation direction corresponds to the imaging range value of a single pixel. With arbitrary points as the starting point and with the imaging range value of a single pixel as the space to segment the smooth gray level curve of a single pixel varying with displacement, the distribution results of gray level with pixel in various possible imaging locations can be obtained theoretically. Then, the minimum value of PVR value is found. If the minimum value is greater than $\sqrt 2 $, the black-white line pair can be distinguished at all imaging locations. If the minimum value is less than $\sqrt 2 $, the black-white line pair cannot be distinguished at the some imaging locations. As the gray level distribution of the black-white line pair image is close to sinusoidal distribution near Nyquist frequency, the moving step of imaging can be reduced by curve fitting, and the curve of pixel gray level changing with displacement is more smooth. Then, the paper proves that a simple curve segmentation method can directly obtain the minimum PVR value, which significantly reduces the data processing capacity of this method. At last, the feasibility and correctness of the method are verified by the experimental measurement for an area array spectral imaging equipment. This method can effectively avoid the defects of existing methods when the resolution of detector is insufficient, the data processing is relatively simple, and the results are reliable, which is conducive to maintaining the consistency of the measurement results of spatial resolution between different experiments. In addition, this method can also be applied to the accurate measurement of the modulation transfer function of the array imaging system, so as to quickly find the measurement target matching the Nyquist frequency of the system.