Digital image processing as an integral component of optical design

The design of modern imaging systems is intricately concerned with the control of optical aberrations in systems that can be manufactured at acceptable cost and with acceptable manufacturing tolerances. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest in a more generalised approach whereby digital image processing is incorporated into the design process and the performance metric to be optimised is quality of the image at the output of the image processor. This introduces the possibility of manipulating the optical transfer function of the optics such that the overall sensitivity of the imaging system to optical aberrations is reduced. Although these hybrid optical/digital techniques, sometimes referred as wavefront coding, have on occasion been presented as a panacea, it is more realistic to consider them as an additional parameter in the optimisation process. We will discuss the trade-offs involved in the application of wavefront coding to low-cost imaging systems for use in the thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems.