Joint Histogram 2 D

I am doing this

Write a MATLAB function which computes the 2D joint histogram, GXY ,

of a pair of images, X and Y, of equal size. Test it on the red and green

components of the Queen Butterfly image.

Display the joint histogram, GXY , as a grey level image.

here is my attempt:

function h=histogramtest

A=imread('queen_butterfly_fish.ppm');
h=zeros(size(A,1),size(A,2));
red=A(:,:,1);
green=A(:,:,2);
row=double(red(:)+1);
col=double(green(:)+1);


%h = zeros(256,256);
for i=1:256
  for j=1:256
  	for k = 1:size(row)
  	 % count number of occurences where i == row(k) and j == col(k)
  	end  
    % set h(i,j) = count value you get from previous loop
  end
end
imshow(h)
end

it's not working at all . Thanks in advance for help in edit the code.

[KSSV]

Why you want to run a loop and count? YOu have functions to do that..read about hist.

[Brave A]

it might a mistakes.

I tried to implement what questions asked, any help?

[Brave A]

I don't want his function becaue I have colored pictured and I want to show in gray. the first part of my code is correct but the second part , is where I am struggling .

Answer 1

[Bruno Luong]

% Test data
A = imread('ngc6543a.jpg');
red=A(:,:,1);
green=A(:,:,2);

% h = histcounts2(green,red,256); % compute
% or plot
histogram2(green(:),red(:),256);

[Brave A]

i don't want to use histogram function. would you plase look to the requiremnt and my code. So in my code first part is correct but the problem is in the second part. the result should be in gray

[Brave A]

you can say I need to implement the function instead of using functions does that for me :)

[Bruno Luong]

Yeah because the loops obviously are wrong. It come down to understand what is an histogram. If it's homework, then I can't help you more.

[Brave A]

hi could you look here please

https://www.mathworks.com/matlabcentral/answers/487763-circulate-matrix-to-perform-eigenvectors

Answer 2

[Bruno Luong]

% Test data
A = imread('ngc6543a.jpg');
red=A(:,:,1);
green=A(:,:,2);

h = accumarray([green(:),red(:)]+1,1,[256 256]);