Fig. 1. Overall frameworkof algorithm

Fig. 2. Enhancement of context-sensitive and context-free. (a) Original image; (b) context-sensitive; (c) context-free

Fig. 3. Visual threshold and image background brightness curve

Fig. 4. (a) CLAHE transform after adaptive brightness equalize; (b) CLAHE transform

Fig. 5. Enhanced image with brightness adjustment module corresponding to different optimal solutions. (a) CLAHE as optimal solution; (b) CLAHE transform after brightness equalize as optimal solution

Fig. 6. Reference image and image to be enhanced and its quality score. (a)-(g) Reference images; (h)-(n) images to be enhanced

Fig. 7. Average score of subjective evaluation

Fig. 8. Average score of NIQE, NIQMC, clarity

Fig. 9. Weak contrast images treated by different methods. (a) Original image; (b) AGWD method; (c) BIQME method; (d) GICE method; (e) ROHIM method; (f) proposed method

Fig. 10. Dark image treated by diffeent methods. (a) Original image; (b) AGWD method; (c) BIQME method; (d) GICE method; (e) ROHIM method; (f) proposed method

Fig. 11. Night image treated by different methods. (a) Original image; (b) AGWD method; (c) BIQME method; (d) GICE method; (d) ROHIM method; (f) proposed method