用matlab分水岭算法做海岸线的提取

先上原图：



下面是程序：

rgb = imread('你图片文件');%读取原图像

I = rgb2gray(rgb);%转化为灰度图像

figure; subplot(121)%显示灰度图像

imshow(I)

text(732,501,'Image courtesy of Corel',...

     'FontSize',7,'HorizontalAlignment','right')

hy = fspecial('sobel');%sobel算子

hx = hy';

Iy = imfilter(double(I), hy, 'replicate');%滤波求y方向边缘

Ix = imfilter(double(I), hx, 'replicate');%滤波求x方向边缘

gradmag = sqrt(Ix.^2 + Iy.^2);%求摸

subplot(122); imshow(gradmag,[]), %显示梯度

title('Gradient magnitude (gradmag)')

L = watershed(gradmag);%直接应用分水岭算法

Lrgb = label2rgb(L);%转化为彩色图像

figure; imshow(Lrgb), %显示分割后的图像

title('Watershed transform of gradient magnitude (Lrgb)')

se = strel('disk', 20);%圆形结构元素

Io = imopen(I, se);%形态学开操作

figure; subplot(121)

imshow(Io), %显示执行开操作后的图像

title('Opening (Io)')

Ie = imerode(I, se);%对图像进行腐蚀

Iobr = imreconstruct(Ie, I);%形态学重建

subplot(122); imshow(Iobr), %显示重建后的图像

title('Opening-by-reconstruction (Iobr)')

Ioc = imclose(Io, se);%形态学关操作

figure; subplot(121)

imshow(Ioc), %显示关操作后的图像

title('Opening-closing (Ioc)')

Iobrd = imdilate(Iobr, se);%对图像进行膨胀

Iobrcbr = imreconstruct(imcomplement(Iobrd), ...

    imcomplement(Iobr));%形态学重建

Iobrcbr = imcomplement(Iobrcbr);%图像求反

subplot(122); imshow(Iobrcbr), %显示重建求反后的图像

title('Opening-closing by reconstruction (Iobrcbr)')

fgm = imregionalmax(Iobrcbr);%局部极大值

figure; imshow(fgm), %显示重建后局部极大值图像

title('Regional maxima of opening-closing by reconstruction (fgm)')

I2 = I;

I2(fgm) = 255;%局部极大值处像素值设为255

figure; imshow(I2), %在原图上显示极大值区域

title('Regional maxima superimposed on original image (I2)')

se2 = strel(ones(5,5));%结构元素

fgm2 = imclose(fgm, se2);%关操作

fgm3 = imerode(fgm2, se2);%腐蚀

fgm4 = bwareaopen(fgm3, 20);%开操作

I3 = I;

I3(fgm4) = 255;%前景处设置为255

figure; subplot(121)

imshow(I3)%显示修改后的极大值区域

title('Modified regional maxima')

bw = im2bw(Iobrcbr, graythresh(Iobrcbr));%转化为二值图像

subplot(122); imshow(bw), %显示二值图像

title('Thresholded opening-closing by reconstruction')

D = bwdist(bw);%计算距离

DL = watershed(D);%分水岭变换

bgm = DL == 0;%求取分割边界

figure; imshow(bgm), %显示分割后的边界

title('Watershed ridge lines (bgm)')

gradmag2 = imimposemin(gradmag, bgm | fgm4);%置最小值

L = watershed(gradmag2);%分水岭变换

I4 = I;

I4(imdilate(L == 0, ones(3, 3)) | bgm | fgm4) = 255;%前景及边界处置255

figure; subplot(121)

imshow(I4)%突出前景及边界

title('Markers and object boundaries')

Lrgb = label2rgb(L, 'jet', 'w', 'shuffle');%转化为伪彩色图像

subplot(122); imshow(Lrgb)%显示伪彩色图像

title('Colored watershed label matrix')

figure; imshow(I),

hold on

himage = imshow(Lrgb);%在原图上显示伪彩色图像

set(himage, 'AlphaData', 0.3);

title('Lrgb superimposed transparently on original image')

最后得到一个清晰的海岸线图像：