Method and system for enhancing image quality

An inspection system for inspecting a sample comprising:

• a charged particle beam generator for generating a primary charged particle beam;
• a condenser lens module arranged below the charged particle beam generator and adapted for condensing the primary charged particle beam;
• a probe forming objective lens module arranged below the condenser lens module and adapted for focusing the condensed primary charged particle beam into a charged particle beam probe;
• a charged particle beam deflection module arranged below the condenser lens module for deflecting the charged particle beam probe to a surface of the sample;
• a secondary charged particle detector module for detecting a secondary charged particle detection signal generated from the sample;
• an image forming module communicated with the secondary charged particle detector module for receiving the secondary charged particle detection signal and forming at one or more frames;
• and
• a noise-filtering module communicated with the image forming module and encoded with a computer program for determining a defect, wherein the computer program performs the following steps:
• recording a sequence of grayscales of a pixel of the frames scanned by the charged particle beam;
• removing extreme values from the sequence of grayscales;
• and determining a nominated grey level of the pixel from remained grayscales.