Fig. 1. Spatial lighting model of measured object and ring light source

Fig. 2. Gray scale in 100 mm×100 mm field of view under ring light source. (a) Plane gray scale; (b) gray distribution of normalized median line in field of view; (c) 3D display of gray scale map

Fig. 3. Simulation image of measured object under ring light illumination. (a) Gray image of measured object; (b) gray scale distribution of cross section at positions 1-5

Fig. 4. Gray distributions of cross section at the center of the measured object under different light source rings

Fig. 5. Dome lighting model

Fig. 6. Gray scale map in 100 mm×100 mm field of view under dome light source. (a) Plane gray scale map; (b) gray distribution of normalized median line in field of view; (c) three-dimensional display of gray scale map

Fig. 7. Simulated image of measured object under dome lighting. (a) Gray image of measured object; (b) gray scale distribution of cross section at position 1-5

Fig. 8. Gray distribution at different positions under two different light sources

Fig. 9. Experiment and light source

Fig. 10. Illumination distribution of individual LED in different light sources

Fig. 11. Wire imaging contrast under different light sources. (a) Wire images under ring light; (b) wire images under dome light; (c) gray scales of ring light images; (d) gray scales of dome light images

Fig. 12. Image gray scale comparison at different positions. (a) Gray scale distributions at different positions under ring light; (b) gray scale distributions in different positions under dome light