With the increasing demand on miniaturization of optical modules, it is important to measure their image quality for consumer electronic devices, such as video cameras, mobile phones, etc. This is because the effect of diffraction arises from the miniaturized optical modules and as a result, it degrades the resolution of the imaging processes. Modulation transfer function (MTF) has been widely recognized as a useful and important tool for assessing the image quality. Therefore, the objective of this paper is to develop a MTF measurement system for the optical modules, on the basis of digital signal processing.
In our approach, a spatial light modulator (SLM) is employed to spatially modulate the light, which is emitted from a white-light LED, with the bar patterns of variable frequencies, the modulated light then goes through the module under test, and it is eventually detected by a charge-couple-device (CCD). Obviously, the mapping from the collection of the modulated light to the output images is treated as a computation kernel of the MTF measurement. The corresponding images formed by the optical module are acquired by a digital signal processor (DSP) based system and they are processed by an algorithm for computing the MTF, which is implemented in the system. Finally, it is found that our experiments give quite satisfactory results.