Contrast-Stretching & Thresholding

%cameraman image contrast_stretching_grayimage_
clc;
clear all;
close all;

%defining points
r1=120; s1=60;
r2=150; s2=130;

%slope
m1 =(s1/r1);
m2 =((s2-s1)/(r2-r1));
m3 =((255-s2)/(255-r2));

%equations of line
k=0:r1;
y1=m1*k;
plot(k,y1);


hold on;

k = r1: r2;
y2 = m2*(k - r1) + m1*r1;
plot (k,y2);

k = r2:255;
y3 = m3*(k-r2) + m2*(r2-r1)+ m1*r1;
plot (k,y3);

xlim([0 255]);
ylim([0 255]);

xlabel('input gray level, r');
ylabel('output gray level, s');
title('Form of transformation');
hold on;


f=imread('cameraman.tif');
[m, n] = size (f);

%contrast stretching
for i = 1:m
    for j = 1:n
        if((f(i,j)>=0) & (f(i,j)<=r1))
        g(i,j) = m1*f(i,j);
        else
            if((f(i,j)>r1) & (f(i,j)<=r2))
            g(i,j) = ((m2*(f(i,j)-r1)+(m1*r1)));
            else
                if((f(i,j)>r2) & (f(i,j)<=255))
                g(i,j) = ((m3*(f(i,j)-r2)+(m2*(r2-r1)+(m1*r1))));
                end
            end
        end
    end
end

figure
subplot(221)
imshow(f)
title('actual image')

subplot(222)
imshow(g)
title('contrast-stretched image')

for i = 1:m
    for j = 1:n
        if((f(i,j)>=0) & (f(i,j)<130))
        g(i,j) = 0;
        else
            g(i,j) = 255;
        end
    end
end


subplot(223)
imshow(f)
title('actual image')

subplot(224)
imshow(g)
title('contrast-stretched image')