Autofocusing of Fresnel zone aperture lensless imaging based on image sharpness metrics

Abstract

Fresnel zone aperture lensless imaging encodes incident light into a hologram-like pattern. However, the uncertain target distance leads to a blurry image with artifacts, which brings challenge to the estimation of object distances. We proposed an autofocusing method for FZA lensless imaging which is a superior solution for distance estimation. The image sharpness metrics are incorporated into the back-propagation process to obtain the focusing distance and reconstruct high-contrast and noise-free images. The Tamura gradient, nuclear norm of gradient and the gradient of the image are combined together to obtain a new evaluation metric. The acquisition accuracy is higher and the time is faster by using this new metric to obtain the focus distance. The proposed method paves the way to the micro sensors.