Fig. 1. Geometry of surface reflection

Fig. 2. Schematic of LED ring array illumination model

Fig. 3. Flow chart of LED ring array illumination design

Fig. 4. Illumination distribution of different radius with ρ=0° in single ring. (a)--(e) Illumination uniformity is 23.85%, 22.50%, 20.35%, 17.79%, and 15.51%, respectively

Fig. 5. Normalized illumination distribution and illumination distribution of central line corresponding to the combination of A3-B1-C1-D1. (a) Illumination distribution; (b) illumination distribution of central line

Fig. 6. Relation between uniformity and irradiating angle

Fig. 7. Light intensity at different irradiating angles. (a) ρ=0°; (b) ρ=20°; (c) ρ=40°

Fig. 8. Normalized illumination corresponding to irradiating angle of 20°. (a) 2D map of illumination distribution; (b) illumination distribution map of central line; (c) 3D map of illumination distribution

Fig. 9. Schematic of experimental system. (a) Designed LED ring array; (b) experimental setup

Fig. 10. 3D sample imaging effect under different illuminating conditions. (a) Sample image; (b) image taken in optimal light environment; (c)--(f) images in non-uniform light environment

Fig. 11. Sample details. (a) 3D sample image in optimal light environment; (b) corresponding gray level map

Fig. 12. Corresponding light spot and gray distribution in optimal light environment. (a) Light spot; (b) 3D gray level distribution in central area