(An) active imaging system for image quality enhancement

Abstract

An optical imaging system has several tradeoffs between performance factors such as image resolution and the depth-of-field, and magnification and the size of the field of view. Therefore the optical system designers have had to compromise between those conflicting performance factors. In this thesis an active optical system is proposed to overcome those limitations. By using innovative optical elements recently popularized such and liquid-crystal spatial light modulator (LC-SLM) with proper image processing methods, those limitations can be overcome. In particular, a depth-of-field extension method using an LC-SLM and a deformable mirror at the pupil plane is proposed to reduce the trade-off between the image resolution and the depth-of-field. The basic idea is to divide the entrance pupil into several concentric annular rings and combining them to restore clear image digitally. Depth-of-field extension by focal plane oscillation, which was already proposed, is combined with the annular division system to enhance the depth extending performance. The images obtained by the depth extension method are found to be vulnerable to image noise and the image quality becomes degraded as the depth-of-field is more extended. To cope with this problem, depth-of-field adaptation scheme is also developed to provide the image with best quality given an arbitrary object distribution. This is to avoid obtaining blurry images due to too small depth-of-field, or noisy images due to too large depth-of-field. For this, the trade-off relationship between the depth-of-field extension range and the image quality was experimentally analyzed and a quality measure based on wavelet transform was proposed to quantify the image qualities. Also, an adaptation scheme to estimate the objects’ depth distribution and the optimal parameter for the best quality image efficiently was proposed. For an application, a microscopic zoom control system was designed using the depth-of-field adaptation con...