A method for personal expertise-independent evaluation of image resolution in scanning electron microscopy

The two conventional methods currently employed for the evaluation of image resolution in scanning electron microscopy are the gap method and a fast Fourier transform (FFT) method. These can be highly dependent on personal expertise on the distinction between signal information and noise contained in a micrograph. Hence, the present paper proposes an alternative method (referred to as a contrast-to-gradient (CG) method) that can determine the image resolution of a micrograph without requiring personal expertise on the judgment of noise. The image resolution in the CG method is defined as a weighted harmonic mean of the local resolution, which is proportional to the quotient of the threshold contrast divided by the local gradient. The local gradient is calculated from the quadratic function that best fits the local pixel intensities over 5 x 5 pixels. It has been shown that the CG method, compared with the FFT method, has a broader range of applications for various types of images, such as low-contrast, noise-containing, filter-processed, highly directional, and quasi-periodic feature images.