Fig. 1. Schematic diagrams of surface reflection phenomena and characteristics. (a) Light reflection phenomena on surfaces with complex microscopic details; (b) surface reflection characteristics based on BRDF theory

Fig. 2. Schematic diagram of imaging of linear light source in the X-direction

Fig. 3. Polarization imaging process. (a) Lightpath with maximum light intensity; (b) lightpath with minimum light intensity

Fig. 4. Reflected luminance. (a) Hybrid reflection; (b) diffuse reflection; (c) specular reflection

Fig. 5. Geometric relationships of the surface normal

Fig. 6. Imaging system in operation

Fig. 7. Calibration board. (a) Original image of the calibration board; (b) standard normal map; (c) measured normal map

Fig. 8. Imaging results of square textured paper. (a)(b) Original images; (c)(d) corresponding normal maps

Fig. 9. Imaging results of paper with horizontal stripes. (a)‒(c) Original images; (d)‒(f) corresponding normal maps

Fig. 10. Imaging results of paper with dotted texture. (a)‒(c) Original images; (d)‒(f) corresponding normal maps

Fig. 11. Imaging results of paper with irregular embossed patterns. (a)‒(c) Original images; (d)‒(f) corresponding normal maps

Fig. 12. Imaging results of paper with regular embossed patterns. (a)‒(c) Original images; (d)‒(f) corresponding normal maps