Fig. 1. Flow chart of multi-scale blood vessel segmentation

Fig. 2. Preprocessed images. (a) Original color image; (b) green channel image; (c) contrast enhanced image by CLAHE

Fig. 3. Gradient amplitudes when σ=1,2,4 pixel. (a) σ=1 pixel; (b) σ=2 pixel; (c) σ=4 pixel

Fig. 4. Maximum principal curvature images when σ=1,2,4 pixel. (a) σ=1 pixel; (b) σ=2 pixel; (c) σ=4 pixel

Fig. 5. Results of post-processing for contour feature image. (a) Laplacian filtered image; (b) energy significant mapping image; (c) image obtained by mathematical morphology processing

Fig. 6. Results of post-processing for detail feature image. (a) Energy significant mapping image; (b) image obtained by mathematical morphology processing

Fig. 7. Fusion process of wavelet transform

Fig. 8. Fusion image with wavelet transform when σ=1 pixel

Fig. 9. Image obtained by multi-scale vascular detection

Fig. 10. Comparison of detail images obtained by multi-scale blood vessel detection. (a) Original color image; (b) contour feature, (c) detail feature, and (d) detail image of wavelet transform fusion at σ=1 pixel; detail images obtained by blood vessel detection when (e) σ=2 pixel and (f) σ=4 pixel; (g) detail image obtained by multi-scale blood vessel detection

Fig. 11. Comparison of blood vessel segmentation effects of retinal images. (a) Original color fundus retinal images; (b) gold standard images; (c) results of single scale vascular segmentation; (d) results of multi-scale vascular segmentation

Fig. 12. 1D cross-section of middle row of marked subarea in the third image in Figs. 11 (c) and (d)

Fig. 13. Blood vessel segmentation results by fusing contour information with detail information at multi-scale or single-scale frames. (a) Results of fusion at multi-scale frame; (b) details of gold standard image; (c) results of fusion at single-scale frame; (d) results of fusion at multi-scale frame

Fig. 14. Results of blood vessel segmentation with and without fusion of contour information and detail information at multiple scales. (a) Without fusion of contour information and detail information; (b) with fusion of contour information and detail information; (c) detailed drawing marked in Fig. 14(a); (d) detailed drawing marked in Fig. 14(b)