Research On The Image Restoration In Wave-front Coding Technology

By adding a special phase plate in general optical systems to modulate the wave-front, making its optical transfer function and point spread function insensitive to defocus, wave-front coding technology can extend depth of focus of optical systems. Optical systems using wave-front coding technology obtain intermediate blurred images from the detector, and an effective digital image restoration technique is combined to get the final clear image.This dissertation focuses on the research of image restoration algorithms suited for wave-front coding systems. The point spread function (PSF) of a wave-front coding system is available and can be obtained by software simulation or experiments. It has a special form different from degradation functions caused by motion or defocus blur. Based on the imaging experiment of actual wave-front coding system, the effects of different restoration algorithms are discussed. We proposed a detailed method to solve problems such as noise amplification and signal-to-noise ratio presence in wave-front coding image restoration and the corresponding solution is verified by experiments. The main contents include the followings:1. The dissertation describes the history and current situation of wave-front coding technology and its image restoration, and analyzes the characteristics of image restoration in the wave-front coding system, as well as the significance of the study.2. The basic theory of digital image restoration is introduced, including the basic concept, problem model, several classic restoration algorithms and evaluation methods of the image quality in image restoration, and briefly describes the noises that impact image restoration effects and various denoising methods.3. The dissertation researches the basic theory of wave-front coding technology, finds cubic phase plate form based on ambiguity function and stationary-phase method, and analyzes its imaging characteristics using optical design software, after fabrication of the lens, the imaging experiments are carried out, discusses imaging effects and extending the depth of focus ability of the wave-front coding technology.4. The dissertation analyzes sources and types of noises in wave-front coding system imaging, establishes the system noise model and frequency signal to noise ratio model. In order to solve the problem of noise amplification in the restoration process, an improved algorithm is introduced. It cooperates wavelet denoising into the traditional LR algorithm. The experimental results show that the new method is effective.5. In order to further improve the resolution of wave-front coding system, super-resolution restoration technology is studied, the dissertation exhibits an image restoration method based on the optimal reconstruction theory. Imaging experiments and restoration simulation find that the optimal reconstruction method is effective to improve the resolution of the wave-front coding system restoration image.