Study of modular transfer function-based optieal low-pass filter evaluation model and experiment

Abstract

To evaluate the performance of optical low pass filter (OLPF) accurately, a new 2D digital imaging system model including an OLPF was created for the first time using the modular transfer function (MTF). An evaluation function was also established based on this model. To manifest the model and its evaluation, three typical OLPFs were studied. The results show that the Δ value of each filter undergoes a slow and slight decrease and then rapidly increases when the ideal optical system cutoff frequency is increased. The optieal system embedded with the 2-chip-4-point type OLPF created a better image than those with the other two OLPF's when the F number is greater than 44; whereas the OLPF of 3-chip-8-point type worked best when the F number is lower than 44 When the F number of the optical system is 28, namely, with a spatial cutoff frequency of 649 lp/mm, the filter of 3-chip-8-point type performs better than that of the 2-chip-4-point and 3-chip-4-point types. The Δ value of the first filter is 283% and 375%, lower than that of the other two filters, respeatively. That is, the filter performance is 283% and 375% higher. Finally, spatial frequency test shows that the moiré fringe and false colors can be seen in the last two pictures, while in the first, these effects are well eliminated. The theoretical calculations agree with the experimental results.