It has been shown that electro-optical imaging systems designed by integrating optics and digital processing provide system-level advantages such as extended depth-of-field and lower optical component costs. In such imaging systems, the strength of the optical aberration or blur can dramatically change with the f-number, and hence different digital filters in the subsequent digital processing are required to correct the captured images at different f-numbers. However, implementing such number of filters in hardware requires expensive computational resources, which in turn increase the overall system cost. In this paper, we propose a simple image filtering approach which uses a weighted sum of a set of component finite impulse response (FIR) filters to effectively apply a different composite FIR filter for each f-number. The simulation results demonstrate that our approach achieves desirable image quality for variable f-numbers, while substantially reducing the complexity in hardware implementation.