A method for generating a feature map used for inspecting a photolithographic mask to identify lithographically significant defects, the method comprising: providing a mask comprising a plurality of printable features and a plurality of non-printable features, the mask configured to achieve lithographic transfer of the printable features onto a substrate using a lithography system; by one or more inspection systems, producing a transmitted light intensity image and a reflected light intensity image of the mask; constructing a band limited spot image based on the transmitted light intensity and reflected light intensity images to reduce noise introduced by the one or more inspection systems; restoring the spot image to a restored mask image to thereby minimize further optical aberrations from the one or more inspection systems in the mask image; based on the restored mask image, generating a non-printable feature map for the non-printable features and printable feature map for the printable features; growing the non-printable feature map while preventing encroachment of such non-printable feature map into the printable features based on the printable feature map; analyzing one or more test images of the mask to detect defects on such mask, wherein a sensitivity level of defect detection is reduced in areas of the one or more test images defined by the non-printable feature map, as compared with areas of the one or more test images that are not defined by the non-printable features map; and wherein generating a non-printable feature map for the non-printable features and printable feature map for the printable features further comprises:: performing a thinning process on the restored mask image to generate a skeleton image; and measuring line widths in the restored mask image using the skeleton image to determine where to measure such line widths, wherein the measured line widths are used to generate the non-printable and printable feature maps by distinguishing between measured line widths that are below or equal to or above a specified threshold value, respectively. providing a mask comprising a plurality of printable features and a plurality of non-printable features, the mask configured to achieve lithographic transfer of the printable features onto a substrate using a lithography system; by one or more inspection systems, producing a transmitted light intensity image and a reflected light intensity image of the mask; constructing a band limited spot image based on the transmitted light intensity and reflected light intensity images to reduce noise introduced by the one or more inspection systems; restoring the spot image to a restored mask image to thereby minimize further optical aberrations from the one or more inspection systems in the mask image; based on the restored mask image, generating a non-printable feature map for the non-printable features and printable feature map for the printable features; growing the non-printable feature map while preventing encroachment of such non-printable feature map into the printable features based on the printable feature map; analyzing one or more test images of the mask to detect defects on such mask, wherein a sensitivity level of defect detection is reduced in areas of the one or more test images defined by the non-printable feature map, as compared with areas of the one or more test images that are not defined by the non-printable features map; and wherein generating a non-printable feature map for the non-printable features and printable feature map for the printable features further comprises:: performing a thinning process on the restored mask image to generate a skeleton image; and measuring line widths in the restored mask image using the skeleton image to determine where to measure such line widths,