Method of microscopic imaging quality evaluation for board lens based on image parameter extraction of pinhole imaging

The modulation transfer function area (MTFA) of pinhole imaging and the MTFA relative variation ratio were used as the image surface parameters to quantitatively evaluate the microscopic imaging quality of the board lens. The light spot images located in different fields of view positions were obtained by using the pinhole imaging method to extract the modulation transfer function (MTF) of microscopic imaging system for board lens. The MTF mathematical model of lens system for board lens was established, and the MTFA in sagittal direction and meridian direction of edge field of view as well as the MTFA relative variation ratio were extracted to measure the microscopic imaging definition and image surface flatness of the measured lens. An experiment which was for measuring the board lens was carried out, and the microscopic imaging performance of the measured lens was quantitatively evaluated by using the proposed model and method. The results show that the Lens 2 can obtain the optimal microscopic imaging quality. The definition value of average power spectrum value (APSV), the gray mean gradient (GMG) and the laplacian summation (LS) were calculated respectively from the RGB bitmap images captured by these measured lens. The results show that the maximum parameter value of the APSV, GMG and LS of Lens 2 bitmap images is equal to 2.720 2, 17.024 4 and 94.921 2, respectively. At the same time, the bitmap images have the highest definition, which is consistent with the image surface parameter evaluation results, indicating that the proposed method used in the quantitative evaluation of microscopic imaging performance of board lens is accurate and effective, which is of great significance and engineering value to improve the online image probe design of the on-line visual ferrograph (OLVF).