Fig. 1. Processing of transmitted images under LIP model

Fig. 2. Under the LIP model, two images are added together

Fig. 3. Processing process of φ function

Fig. 4. Processing process of φ^-1 function

Fig. 5. Four-direction Sobel operator templates. (a) x-axis direction template; (b) y-axis direction template; (c) 45° direction template; (d) 135° direction template

Fig. 6. 3 pixel×3 pixel area

Fig. 7. Gradient image comparison results. (a) Test image; (b) gradient image of proposed algorithm; (c) gradient image of Ref. [14] algorithm; (d) traditional Sobel algorithm gradient image

Fig. 8. Image of real experimental platform

Fig. 9. Internal structure of the experimental platform

Fig. 10. Principle block diagram of experimental platform

Fig. 11. Image of measured target. (a) Car image; (b) triangle base image; (c) triangle base and number plate combination image

Fig. 12. Results of algorithm flow. (a) Original image; (b) filtered image; (c) gradient image; (d) final result image

Fig. 13. Comparison of edge detection results. (a) Original image; (b) traditional Canny algorithm; (c) Sobel algorithm; (d) Ref. [14] algorithm; (e) proposed algorithm