Fig. 1. Gray distributions of different areas. (a) Background area; (b) speckle area

Fig. 2. Gaussian pyramid and Laplacian pyramid

Fig. 3. Comparison of original image and Laplacian pyramid image. (a) Original image; (b) LP₀ image

Fig. 4. Speckle area extraction based on second-order gradient entropy and Laplacian pyramid weighted entropy. (a) Extraction result based on second-order gradient entropy; (b) entropy value distribution histogram of second-order gradient entropy; (c) extraction result based on weighted entropy; (d) entropy value distribution histogram of weighted entropy

Fig. 5. Flow chart of speckle area extraction algorithm

Fig. 6. Original image 1 and comparison of extraction results of two methods. (a) Original image 1; (b) extraction result based on second-order gradient entropy; (c) extraction result based on weighted entropy

Fig. 7. Original image 2 and comparison of extraction results of two methods. (a) Original image 2; (b) extraction result based on second-order gradient entropy; (c) extraction result based on weighted entropy

Table 1. Calculation time for comparison