One just-focused composite image of a scanning electron microscope (SEM) has been reconstructed from just-focused image areas obtained from different images taken with a series of different focus lengths. The practicable evaluation method for the focus of each image plays an important role for this reconstruction. We selected eight focus-evaluation methods described in the Shape From Focus (SFF) method1∼4) usually used for optical images; the Fourier transform, the gradient magnitude maximization, the high-pass filtering, the gray-level maximization, the gray-level variance, the Sum-Modulus-Difference (SMD), the histogram entropy and the histogram of local variations methods. They were applied to three different series of SEM images and evaluated, where the high-pass filtering method is shown to be the most reliable one for the SEM image. The gray-level variance, the SMD and the gradient magnitude maximization methods are also shown to be the applicable methods.
