Histogram threshold Value Method

The histogram threshold method is  implemented by using MATLAB histogram threshold method:
clc;clear;close;
I=imread (' e:\role0\003i.bmp ');
I1=rgb2gray (I);
Figure;
Subplot (2,2,1);
Imshow (I1);
Title (' Grayscale image ')
grid on;% display gridlines axis on
;                  % display coordinate system
[M,n]=size (I1);                            % measurement image size parameter
gp=zeros (1,256);                           % pre-created vector for
k=0:255
    GP (k+1) =length (Find (I1==k))/(M*n) that holds the probability of grayscale occurrence;    % calculates the probability of each level of grayscale appearing, storing it in GP in the corresponding position
end
subplot (2,2,2), bar (0:255,GP, ' g ')                   % plotting histogram
title (' Grayscale histogram ')
Xlabel (' Gray value ')
ylabel (' probability of occurrence ')
I2=IM2BW (i,150/255);
Subplot (2,2,3), Imshow (I2);
Title (' Segmented image of threshold 150 ')
grid on;                  % Display grid line
axis on;                  % display coordinate system
I3=IM2BW (i,200/255);   %
subplot (2,2,4), Imshow (I3);
Title (' Segmented image of Threshold 200 ')
grid on;                  % Display grid line
axis on;                  % Display coordinate system