Fig. 1. Flowchart of the detection algorithm based on Sobel filtering

Fig. 2. Microscopic image of multilayer optical data storage lattice

Fig. 3. (a) Original image; (b) preprocessed image

Fig. 4. Binary image after binarization with variable threshold

Fig. 5. Draw grids for a lattice diagram

Fig. 6. Images of shallow layer .(a) Original image; (b) image after Sobel filtering; (c) grid image

Fig. 7. Images of deep layer .(a) Original image; (b) image after Sobel filtering; (c) grid image