Fig. 1. Ray angle diagram

Fig. 2. Relationship between n^Tv and observation of different materials. (a) Blue fabric; (b) brass; (c) specular white phenolic; (d) black obsidian

Fig. 3. Method framework

Fig. 4. Effects of elevation angle on the following factors. (a) Relative error of n^Tl; (b) overlapped region ratio; (c) condition number; (d) angular error of surface normal

Fig. 5. Rendered images of rabbit and ball model

Fig. 6. Comparison of normal vector recovery maps of four materials (from top to bottom: pvc, alum-bronze, ipswich-pine-221, color-changing-paint2)

Fig. 7. Comparison of four material normal vector angular errors (from top to bottom: pvc, alum-bronze, ipswich-pine-221, color-changing-paint2)

Fig. 8. Angular error of synthetic surface normal vector based on MERL dataset

Fig. 9. Device concept map

Fig. 10. Images of the copper bullet under four lights

Fig. 11. Bullet recovery normal map and bump map. (a) Recovery map of surface normal; (b) bump map