With the latest electronic devices, semiconductor features are very small, and it is very important to control the pattern size and variation. Scanning electron microscopes (SEMs) generate images of these patterns by detecting secondary electrons emitted from incident electrons. These images have noise that must be removed to properly measure pattern variation. Typical filtering methods, such as a box or Gaussian filter, introduce undesired effects into the statistical analysis. The authors have developed a way to reduce image noise without filtering. In this presentation, we will discuss about how to remove image noise by generating artificial SEM images.