Histogram Processing in MATLAB

     Read and Plot the histogram of dark, bright, Low contrast and High contrast image without using built-in function. Verify with the built-in function imhist.

       CODE :

clc; clear all;
img1=imread('hist1.jpg');
img2=imread('hist2.jpg');
img3=imread('hist3.jpg');
img4=imread('hist4.jpg');
subplot(431), imshow(img1), title('Dark image')
subplot(434), imshow(img2), title('Bright image')
subplot(437), imshow(img3), title('Low contrast image')
subplot(4,3,10), imshow(img4), title('High contrast image')

for a=2:3:11
    if(a==2)
        img=img1;
    elseif(a==5)
        img=img2;
    elseif(a==8)
        img=img3;
    else
        img=img4;
    end

[M, N]=size(img);
histbar=zeros(1,256);
for i=1:M
    for j=1:N
            v=img(i,j);
            histbar(v+1)=histbar(v+1)+1;
    end
end
subplot(4,3,a), bar(histbar);
if (a==2), title('Histogram Using code'); end
subplot(4,3,a+1), imhist(img);
if (a==2), title('Histogram using Built-in function'); end
end

OUTPUT RESULT :

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