Methods and systems for detecting defects on a specimen are provided. One system performs double detection in which at least one of the reference images compared to a test image is a computed reference image generated from multiple images corresponding to the test image. The other reference image may or may not be computed from more than one of the multiple images. Such a computed reference image may also be a median-based computed reference generated from multiple-median images generated from different subsets of images in a job of images generated by an inspection subsystem for a specimen. Such a system may also group images for a die row on a specimen into different jobs based on color so that different jobs have different color value ranges. Such grouping may also be performed so that each of the jobs includes a number of images greater than a predetermined, minimum job size.