A method to measure the modulation transfer function of Bayer filter color camera

Duan, Yaxuan; Liu, Shangkuo; Yongquan, Chen; Xue, Xinyu; Jianke, Zhao; Gao, Limin

doi:10.7498/aps.66.074204

Cited by 3 publications

(1 citation statement)

References 18 publications

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“…MTF is an accurate and objective evaluation index of imaging quality, and it is one of the most important indicators of image quality [3][4][5]. The methods most commonly used to measure MTF are the slit method [6,7], the contrast method [8], and the slanted-edge method [9][10][11]. The measurement principle of the slit method is to obtain the MTF by Fourier transform of the line spread function (LSF) of the slit image.…”

Section: Introductionmentioning

confidence: 99%

Research on the Modulation Transfer Function Detection Method of a Bayer Filter Color Camera

Fan

Wei

et al. 2023

Sensors

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Bayer filter color cameras are more and more widely used in the field of aerospace remote sensing, but the Bayer filter causes great degradation in image quality; therefore, obtaining a means of achieving the high-precision measurement of the modulation transfer function (MTF) of Bayer filter color cameras is an urgent problem. In order to solve this problem, this paper develops a slanted-edge method via three steps: the detection of the slanted edge, the acquisition and processing of the edge spread function (ESF), and the acquisition and processing of the line spread function (LSF). A combination of the Canny operator and Hough transform is proposed for the detection of the slanted edge, which improves the fitting accuracy and anti-interference ability of the algorithm. Further, the Canny operator is improved by constructing an adaptive filter function and introducing the Otsu method, which can more effectively smooth the image and remove its false edges. A method of processing ESF data by combining cubic spline interpolation and Savitzky–Golay (SG) filtering is proposed, which reduces the effects of noise and the non-uniform sampling of ESF on MTF. A method of LSF processing using Gaussian function fitting is proposed to further reduce the effect of noise on MTF. The improved algorithm is verified by the MTF measurement test applied to a specific type of Bayer filter color space camera. The simulation and test results show that the improved slanted-edge method discussed in this paper has greater precision and a better anti-interference ability, and it can effectively solve the difficult problem associated with MTF detection in Bayer filter color space cameras.

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Section: Introductionmentioning

confidence: 99%

Research on the Modulation Transfer Function Detection Method of a Bayer Filter Color Camera

Fan

Wei

et al. 2023

Sensors

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Improved method for modulation transfer function measurement of Bayer color cameras

Fan,

Wei,

Wang

et al. 2023

Appl. Opt.

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Aiming at the difficulty of detecting the modulation transfer function (MTF) of Bayer color cameras during focusing, the traditional scheme is modified in this paper. First, through analysis, it is found that the MTF of the Bayer detector decreased substantially compared to the monochromatic detector, which was caused by the loss of a large amount of light from the Bayer detector. When the MTF is calculated for the color image after de-mosaicing, the degradation of image quality leads to the inability to obtain the full-frequency MTF curve. Therefore, this paper proposes a solution to detect the MTFs of the three primary colors in the Bayer image individually, and then weight the MTFs of each primary color to obtain the MTF of the color image based on the calibration results of the light source. Then, considering the steps of differentiation and Fourier transform in the slanted-edge method, this paper solves the problem of non-uniform sampling of edge spread function by using the modification of the slanted-edge method with non-uniform Fourier transform. Finally, the optimal imaging position of a certain type of Bayer color camera is determined using the methods proposed in this paper. Simulation and test results verify the effectiveness and accuracy of the methods in this paper.

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Influence of spectral characteristics of light sources on measuring space camera modulation transfer function

Liu¹,

Wang²,

Li³

et al. 2021

Acta Phys. Sin.

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Modulation transfer function (MTF) measurement is a major means to evaluate the imaging quality of a space camera. The influence caused by the spectral characteristic of light source on the MTF results is not negligible, because the transmittance and color aberration of optical systems, and quantum efficiency of the space camera detectors are all spectrally related. Thus, MTF results tested by different light sources are different from each other. To address this problem, we propose a method to analyze the influence of spectral characteristics of light sources on measuring the MTF of space cameras. In addition, the devices and methods are designed to calibrate the spectral response and monochrome point spread function (PSF) of space camera. A Sigma lens (focal length: 1000mm, F number: 5.6) and a Cannon EOS 5DSR camera (pixel size: 4.14 μm) are combined into an experimental space camera, whose spectral response is calibrated with a monochromator (Omno30300, NBeT) and a spectral radiometer (FieldSpec, ASD). We calibrate the monochrome PSF of the Sigma lens with the same monochromator and a CCD (PIXIS 1024, Princeton Instruments, pixel size: 13 μm) micro-measuring system (20X objective). During the calibration of spectral response and monochrome PSF, the same collimator (focus: 5000 mm, F number: 10) is used. With using the proposed method and those calibrating data, we compute the theoretical values of the MTF of a space camera measured separately with five different light sources. The results indicate that MTF measured by a xenon lamp is greatly different from those MTFs measured by the other four light sources. Comparisons of those theoretically calculated MTFs, separately, show that the MTF measured by a tungsten halogen lamp is greater than the MTF measured by a xenon lamp at each spatial frequency. The deviation between those two lamps reaches a maximum value of 0.075 in the medium-high frequency zone. Furthermore, in order to verify those theoretical conclusions, a platform including a collimator and the previous space camera is constructed. The MTFs measured by a tungsten halogen lamp and a xenon lamp are computed with the slanted-edge method respectively. The results demonstrate that the distributions and deviations of the MTFs tested by those two lamps are identical to those theoretical results at each spatial frequency, with the maximum deviation being 0.057. The theoretical and experimental results demonstrate that the suggested method can accurately calculate the influence of spectral characteristics of light sources on measuring MTF of space cameras. The proposed method can also be adopted to investigate the influence of spectral characteristics of light sources on MTF of optical systems in the design or test stages.

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A method to measure the modulation transfer function of Bayer filter color camera

Cited by 3 publications

References 18 publications

Research on the Modulation Transfer Function Detection Method of a Bayer Filter Color Camera

Research on the Modulation Transfer Function Detection Method of a Bayer Filter Color Camera

Improved method for modulation transfer function measurement of Bayer color cameras

Influence of spectral characteristics of light sources on measuring space camera modulation transfer function

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