Test object image preprocessing for modulation transfer function calculation in the testing of optical systems

Letova E.Y., Ivanova, T.V., Zavgorodnyi, D.S.

For Russian citation (Opticheskii Zhurnal):

Летова Е.Ю., Иванова Т.В., Завгородний Д.С. Предварительная обработка изображений тест-объектов для вычисления функции передачи модуляции при контроле оптических систем // Оптический журнал. 2025. Т. 92. № 6. С. 97–107. http://doi.org/10.17586/1023-5086-2025-92-06-97-107

Letova E.Yu., Ivanova T.V., Zavgorodniy D.S. Test object image preprocessing for modulation transfer function calculation in the testing of optical systems [in Russian] // Opticheskii Zhurnal. 2025. V. 92. № 6. P. 97–107. http://doi.org/10.17586/1023-5086-2025-92-06-97-107

For citation (Journal of Optical Technology):

Abstract:

Subject of study. Preprocessing methods for slit and pinhole object images for the modulation transfer function calculation are discussed, and the method considering the finite size of the object in modulation transfer function calculation is shown. The influence of background and detector noise suppression and the scattering spot center calculation methods on the final error of the modulation transfer function is demonstrated. Aim of study. Data preprocessing (background and noise suppression, cropping and scattering spot center search) and modulation transfer function calculation using test objects images for the hardware-software complex of optical systems automated testing. Method. The preprocessing methods are analyzed using test object images taken with two lenses on the test bench. The modulation transfer function calculation error in cases of applying different preprocessing methods is considered the maximum absolute deviation from the reference graph obtained with another testing method or calculated theoretically when the tested lens was designed. Main results. The error analysis of the modulation transfer function calculation showed that the background correction, influenced by the noise rejection method, has the greatest effect on the calculation results. A median filter and the repetitive background subtraction method are suggested to suppress random noise and background illumination. Moreover, due to the necessity of object size corrections, it is proposed to divide the modulation transfer function by the object spectrum. Furthermore, the square mass center method is recommended to locate the scattering spot center, as it is required to be found with minimum error. Practical significance. The work results will raise the accuracy of control methods based on the test object images in optical fabrication, particularly in optical instruments quality assessment. In addition, the optical testing process complexity will be reduced, and the time spent on the optical systems assessment will be decreased.

Keywords:

digital image processing, noise filtration, background correction, scattering spot center, point spread function, line spread function, modulation transfer function, optical systems testing, optical system quality characteristics

OCIS codes: 100.2000, 110.3000, 110.4100

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