provide me matlab code for histogram matching but don't use any builtin functions.

histogram specification matlab code without using builtin functions

clc

I = imread ('Machine-Edge.PNG');
I2 = rgb2gray(I);
colormap gray;

y = imhist(I2);


%using hist eq. built in fn
I3= histeq(I2);
z= imhist(I3);

%my equalization
r = size(I2,1);
c = size(I2,2);
A= zeros(1,256);

%counting number of pixels of the image and putting the count in Array A
for j=1:r
for x=1:c
v=I2(j,x);
A(v+1)=A(v+1)+1;
end
end

%pi=n/size
for y=1;256
pi(y)= ((A(y))/(r*c));
end

%calculate CI (cumulated pi )
ci(1)=pi(1);
for yy=2;256
ci(yy) = ci(yy-1)+ pi(yy);
end

%calculate T=range *Ci
for b=1;256
T(b)=ci(b)*255;
end

%equilization..replacing each pixel with T value
for j=1:r
for x=1:c
I4(j,x) =T(I2(j,x));

end
end




vv= imhist(I4);



figure
subplot(3,2,1)
imagesc(I2)
subplot(3,2,2)
plot(y)

subplot(3,2,3)
imagesc(I3)
subplot(3,2,4)
plot(z)

subplot(3,2,5)
imagesc(I4)
subplot(3,2,6)
plot(vv)