波前编码超分辨成像技术

波前编码作为一种经典的计算成像技术,以能够大幅度拓展光学成像系统的焦深而闻名,并得到了学术界及工业界长期的关注。实际上,除了焦深的拓展,波前编码还具备实现超分辨率成像的潜力,而这在已有的研究中鲜有讨论。一方面,相位掩膜板的引入在降低光学系统传递函数并使其对离焦不敏感的同时,也有效降低了欠采样数字成像系统中的混叠效应,从而提供了更适合于进行超分辨率重构的数据源。另一方面,相位掩膜板所引起的点扩散函数支持域的巨大化效应使得以数字的方式、从采样间隔可以被认为是无限小的、理想的光学焦平面点扩散函数来计算与特定探测器物理像元大小相对应的采样点扩散函数成为可能。因此,从这两个特点出发,提出了一种为波前编码系统定制的、基于单帧图像放大的超分辨率重构算法,并且研制了原型样机对超分辨率的效果进行了检验。试验表明:焦距50 mm/F数4.5的Cooke三片系统除了焦深拓展超过20倍且具有接近衍射受限成像品质之外,利用复原算法能够实现至少3倍的高品质超分辨率重建效果。

Wave-front coded super-resolution imaging technique

Wave-front coding is a classical computational imaging technique and famous for its capability in extending the depth of focus(DOF) of incoherent imaging system. In fact, besides the DOF extension, this technique has the potentials in realizing super-resolution imaging, which is rare to be investigated in existing literatures. On the one hand, the introduction of phase mask makes defocus invariance of optical transfer function(OTF) possible and the dramatic decrease of modulus of OTF alleviates the aliasing effect owned by most digital imaging systems. In this case, a better image data suitable for super-resolution imaging could be provided. On the other hand, the prominent expansion of point spread function(PSF) allows us to obtain the real sampled PSF corresponding to any specific pitch size in a digital way using the ideal continuous optical PSF whose sampling interval could be considered as unlimitedly small. Therefore, based on these two characteristics, an amplification based single image super-resolution reconstruction algorithm was especially designed for wave-front coded imaging system and an experimental prototype camera has been fabricated to verify the effectiveness of the algorithm. The results demonstrate that the extended DOF which is more than 20 times original DOF has been obtained and at least 3X super-resolution reconstruction effect could be achieved. Besides that, the quality of reconstructed image approaches the diffraction limited level.