Cropping a bounded area using image processing

Hello everyone. I want to crop the traced area with image processing. What is the steps to do it?

My Code:

clc
clear all
close all


ei = 25;
st = 35;

k=ei*st;
img = imread('rrr.jpg');

h = ones(ei,st)/k;
I = imfilter(img,h,'symmetric');

figure
subplot(3,3,1), imshow(img), title('Orginal');
subplot(3,3,2), imshow(I), title('Filtered Image');

%Converting to BW
Igray = rgb2gray(I);
subplot(3,3,3), imshow(Igray), title('Grey');
I1 = imadjust(Igray,stretchlim(Igray),[]);
level = graythresh(I1);
BWj = imbinarize(I1,level);
dim = size(BWj);
IN = ones(dim(1),dim(2));
BW = xor(BWj,IN);  %Inverting
subplot(3,3,4), imshow(BW), title('Black and White');

%Finding of an initial point
row = round(dim(1)/2);
col = min(find(BW(row,:)));

%Tracing
boundary = bwtraceboundary(BW, [row, col], 'W');

subplot(3,3,5), imshow(img), title('Traced');
hold on;

%Display traced boundary
plot(boundary(:,2),boundary(:,1),'g','LineWidth',2);
hold off
% 

The Output:

Answer 1

[yanqi liu]

clc
clear all
close all


ei = 25;
st = 35;

k=ei*st;
img = imread('rrr.jpg');

h = ones(ei,st)/k;
I = imfilter(img,h,'symmetric');

figure
subplot(3,3,1), imshow(img), title('Orginal');
subplot(3,3,2), imshow(I), title('Filtered Image');

%Converting to BW
Igray = rgb2gray(I);
subplot(3,3,3), imshow(Igray), title('Grey');
I1 = imadjust(Igray,stretchlim(Igray),[]);
level = graythresh(I1);
BWj = imbinarize(I1,level);
dim = size(BWj);
IN = ones(dim(1),dim(2));
BW = xor(BWj,IN);  %Inverting
subplot(3,3,4), imshow(BW), title('Black and White');

%Finding of an initial point
row = round(dim(1)/2);
col = min(find(BW(row,:)));

%Tracing
boundary = bwtraceboundary(BW, [row, col], 'W');

subplot(3,3,5), imshow(img), title('Traced');
hold on;

%Display traced boundary
plot(boundary(:,2),boundary(:,1),'g','LineWidth',2);
hold off
% 

% crop it
[r,c] = find(BW);
rect = [min(c) min(r) max(c)-min(c) max(r)-min(r)];
img_rect = imcrop(img, rect);
subplot(3,3,6), imshow(img_rect), title('Croped');