Fig. 1. Denoising and edge enhancement of sea sky image

Fig. 2. Design of six equal directional filters. (a) Distance weights of filters; (b)-(g) filters in six direction

Fig. 3. Processing results of six directional filters. (a) Original images; (b) processing results of each directional filter

Fig. 4. Processing results of directional competitive code. (a)(d) Original images; (b)(e) directional response images after competitive code; (c)(f) phase coding images after screening

Fig. 5. Scan lines extracted from phase coding groups. (a) Cumulative edges response for sea-sky line scanning; (b) phase coding groups marked by scan lines direction; (c) distribution of edges response intensity in the direction of scan line

Fig. 6. Difference of scan parallel lines

Fig. 7. Comparison of sea sky line detection results of typical sample image. (a1)-(a6) Extraction results of Radon transform; (b1)-(b6) extraction results of phase encoding preprocess with Radon transform; (c1)-(c6) extraction results of Hough transform; (d1)-(d6) extraction results of direction encoding preprocess with Hough transform; (e1)-(e6) extraction results of proposed method

Table 1. Comparison of sea sky line detection results of different methods