Assessment and correction of geometric distortions in low-magnification scanning electron microscopy images

Abstract

A method is introduced to assess and correct the geometric distortions which frequently occur in low-magnification scanning electron microscopy (SEM) images. Such images typically exhibit a complex pattern of varying deviations from orthogonality which cannot be adequately corrected by simple geometric transformations such as shifting, scaling, rotation, or shearing. A suitable approach to rectify low-magnification SEM images is polynomial warping, a correction procedure which also accomplishes rubber sheet transformation. To demonstrate the approach, a reference grid for low magnifications has been scanned at 40- and 55-fold magnifications by means of a microanalyzer. Calculated geometric distortions range from 1.5 to 3.5% of the image dimensions; applying polynomial warping, distortions could be reduced to approximately 0.1% of the image dimensions. Because of its easy application and the widespread availability in image processing packages, polynomial warping can be recommended as a routine procedure for rectifying low-magnification SEM images.