Study On MTF Measurement Of CCD Camera

Modulation Transfer Function is an important indicator of performance evaluation of optical imaging system, which reflects the spatial frequency response characteristics of imaging system objectively, and it is a objective criteria for measuring the image quality of the camera. Photoelectric imaging system can be approximately as a linear shift invariant system on the premise that MTF is suitable for performance evaluation of the imaging system. In recent years based on the modulation transfer function of image quality analysis testing technology is through collecting the image of the test target, then processing the datas to calculate the modulation transfer function. It is one of the common methods currently of measuring the modulation transfer function because of its simple structure of system and strong practicability.In this paper, the basic theory of the modulation transfer function and measurement technology of the modulation transfer function of CCD camera were studied. An improved method is presented based on the slanted-edge method. It uses the Canny algorithm to detect edge in the acquired image, and calculate the high threshold which is significant to the Canny algorithm by using the Otsu algorithm combined with the bimodal characteristics of the edge image histogram. Then two-dimensional edge data sampled with subpixel spacing from a region along the direction of the detected edge is reprojected to a one-dimensional array of sub-pixel bins, the ESF is obtained after averaging under improving the sampling rate. It increases the signal-to-noise ratio of the measurement. It not only reduces the signal aliasing, but also suppressed the impact of noise amplification brought from differential process in the edge method more effectively. The maximum deviation from the theoretical simulation is 0.0071. The experimental value is compared with theoretical value of the system at the Nyquist frequency, the error is within 2%. The experiment has proved the accuracy of this method. We use this method to test the MTF of CCD camera in the laboratory, and analyze the influences of parameter settings including different contrast of images and different angles of edge images on accuracy of the MTF measurement. The experiment has proved the conclusion from simulation.We analysis the principle of the oblique slit method, and use this method to calculate the modulation transfer function of the same CCD camera in the laboratory. Compared with the results calculated by the improved slanted edge method, the error is within 5%, which further validates the accuracy of the improved slanted edge method.