Contrast stretching in MATLAB

     Increase the dynamic range of gray values in the input image.

Read contrast.jpg image which is a low contrast image. Apply the transformation such that r₁=r_min, S₁=0, r₂=r_max, S₂=L-1. Plot the transformation function and display the contrast stretched image.

CODE:

clc; clear all;

%% Reading an image

a1=imread('contrast.jpg');

a=double(a1);

[row,col]=size(a);

%% Transformation function (r1,s1)=(rmin,0), (r2,s2)=(rmax,255)

t=0:255;

x1=0*(t>=0 & t<=100); 

x2=7.285*(t-100).*(t>100& t<135);          

x3=255*(t>=135 & t<=255);

x=x1+x2+x3;

%% Obtaining contrast stretched image

for n=1:row

    for m=1:col

        out(n,m)=x(a1(n,m)+1);

    end

end

out1=imadjust(a1,stretchlim(a1),[]);

plot(x)

grid on;

xlabel('Intensity in input image');

ylabel('Intensity in output image')

title('Transformation function')

figure()

subplot(131), imshow(a1), title('Original image')

subplot(132), imshow(uint8(out)), title('Contrast Stretching(using code)')

subplot(133), imshow(out1), title('Contrast Stretching(using stretchlim)')

OUTPUT RESULT:

Transformation Output