Shape-from-focus reconstruction using block processing followed by local heat-diffusion-based refinement

Abstract

Shape from focus (SFF) is a method of recovering the three-dimensional shape of objects from the image sequence through various focusing measurement operators, and is widely used in the fields of medical diagnosis, PCB inspection, industrial manufacturing, and robotic operations. In SFF, the wrong focus measurement causes an inaccurate reconstruction of the object. Generally, to improve the accuracy of focusing measurements, many focus measure (FM) operators are proposed, which is a method that improves the focus volume (FV) performance. However, due to the influence of blur diffusion, which refers to the overlapping of blur circles between different regions, the calculation results of the FM operator in the local window often do not meet the stability requirements of complex scenarios. It is difficult to provide high-precision reconstruction results in practical applications. To overcome this limitation, we proposed an SFF framework based on block processing and heat-diffusion refinement to obtain a refined depth map (RDM). The acquisition of an RDM is mainly divided into two steps. First, the image is divided into blocks to reduce the effect of blur diffusion, and the FM operator is used to calculate the focus measurement value of each block to form the FV. The initial depth map (IDM) is obtained by searching for the best focus position in the FV. The second step is to refine the IDM based on the heat-diffusion principle to obtain the best focus position for all pixels in each block and derive the RDM. The results of experiments conducted on synthetic and real objects demonstrate the superiority of our method in terms of accuracy and its high stability in different application scenarios.