1. An inspection method comprising: providing a patterned object to be inspected and compared with a reference; inspecting the patterned object and providing an output of information relating to visually sensible characteristics of the patterned object, said output of information comprising gray level information regarding the patterned object; converting said gray level information into binary level information regarding the patterned object, the gray level to binary level conversion being carried out at subpixel accuracy; comparing binary level information relating to visually sensible characteristics of the patterned object to binary level information relating to corresponding visual sensible characteristics of the reference; and comparing gray level information relating to visually sensible characteristics of the patterned object to gray level information relating to corresponding visually sensible characteristics of the reference.