Fig. 1. Measurement system

Fig. 2. Flow chart of the center extraction of the light bar

Fig. 3. True light spot image

Fig. 4. True light knife center

Fig. 5. Spot plots with different noise levels

Fig. 6. Results by three clustering methods

Fig. 7. The light knife center extracted by the steger algorithm + median filtering

Fig. 8. The light knife center extracted by the skeleton direction template method+ median filtering

Fig. 9. The light knife center extracted by the proposed method

Fig. 10. Localized enlarged image of the light knife center

Fig. 11. Measurement setup

Fig. 12. Results obtained by the three clustering methods

Fig. 13. Three real spot images pre-processed by proposed method

Fig. 14. The optical knife center extracted by different methods