How to apply Threshold to an image in MATLAB ?

Exercise: Apply thresholding to the original image such that r₁= r₂=mean gray level. Display the result. (Hint: use built-in function im2bw.)

 CODE:

clc; clear all;

%% Reading an image

a1=imread('contrast.jpg');

a=double(a1);

[row,col]=size(a);

%% Calculating mean gray level

sum = 0;

for i=1:row

    for j=1:col

        sum=sum+a(i,j);

    end

end

avg=sum/(row*col);

%% Transformation function

t=0:255;

x1=0*(t>=0 & t<avg); 

x2=255*(t>=avg & t<=255);

x=x1+x2;

%% Obtaining contrast stretched image

for n=1:row

    for m=1:col

        out(n,m)=x(a1(n,m)+1);

    end

end

out1=im2bw(a1);

plot(x)

grid on;

xlabel('Intensity in input image');

ylabel('Intensity in output image')

title('Transformation function')

figure()

subplot(311), imshow(a1), title('Original image')

subplot(312), imshow(uint8(out)), title('Thresholding(using code)')

subplot(313), imshow(out1), title('Thresholding(using im2bw)')

OUTPUT RESULT:

Transformation Function