Fig. 3
From: Detection of surface defects and subsurface defects of polished optics with multisensor image fusion
Imaging results and etching verification of SDs and covered SSDs. a b Superposition images, there are SDs in the figures (surface scratches in red areas). c d e f Superposition images, there are covered SSDs in the figures (polishing points and scratches in green areas). g h Superposition image before etching and its bright image after etching, there is a SD (shallow surface scratch) which disappears after etching, and a covered SSD (polishing scratch) which is exposed after etching