1. A method for inspecting a wafer including a multiplicity of dies, the method comprising: dividing an image of at least a portion of said wafer into a plurality of sub-images each representing a sub-portion of said wafer; and selecting at least one defect candidate within each said sub-image, by comparing each sub-image to a corresponding sub-image of a reference comprising a representation, which is assumed to be defectless, of said portion of said wafer.