how to extract the portion of an image specified by an edge in matlab

i have write the code to convert the image into three different colors and i applied an edge filter, i added the edge and original image now i need to get only leaf portion of the image

my code is

clc
close all;
clear all;
[fname path]=uigetfile('*.*','insert the pic');
a=imread(fname);
figure(1);
imshow(a)
w=0;d=0;z=0;
b=ones(size(a,1),size(a,2),size(a,3));

for i=1:size(a,1)
    for j=1:size(a,2)
        for k=1:size(a,3)
            if a(i,j,2)>a(i,j,1)+5 && a(i,j,2)>a(i,j,3)+5
                b(i,j,1)=255;
                b(i,j,2)=0;
                b(i,j,3)=0;
         end
        end
    end
end
figure(2);
imshow(uint8(b));

for i=1:size(a,1)
    for j=1:size(a,2)
        for k=1:size(a,3)
            if a(i,j,1)>170 || a(i,j,2)>170|| a(i,j,3)>200-30
                b(i,j,1)=0;
                b(i,j,2)=255;
                b(i,j,3)=0;
         end
        end
    end
end
figure(3);
imshow(uint8(b));

%         se=strel('line',1,0);
%         im1=imerode(b,se);
%         figure(4);
%         imshow(im1);
%        
%         

%  for i=1:size(a,1)
%     for j=1:size(a,2)
%         for k=1:size(a,3)
%             if im1(i,j,1)==0 && im1(i,j,2)==0 && im1(i,j,3)==0
%                 b(i,j,1)=255;
%                 b(i,j,2)=0;
%                 b(i,j,3)=0;
%                 
%             end
%          
%         end
%     end
%  end
% figure(5);
% imshow(uint8(b));

g=rgb2gray(uint8(b));
s=edge(g,'sobel');
figure(4);
imshow(s);

gd=im2double(g);
od=im2double(a);

re=bsxfun(@minus,od,gd);
figure(5);
imshow(re);

s=imcrop(re);
figure(6);
imshow(s);