Selecting high intensity histogram from a single image?

Dear Readers,

I have splitted a single image into 4 splitted images. I am interested to find the historam of each image, and then want authomatically select the high intensity histogram region/or high intensty region. The code is as following. Image has been also attached.

clear all;
close all;
I=imread('1.jpg');
subplot 334
imshow(I);
[r c p]= size(I);%r-rows,c-columns,p-planes
A=I(1:r/2,1:c/2,:);
B=I(1:r/2,c/2+1:c,:);
C=I(r/2+1:r,1:c/2,:);
D=I(r/2+1:r,c/2+1:c,:);
subplot 332
imshow(A);
title('Image part 1');
subplot 333
imshow(B);
title('Image part 2');
subplot 335
imshow(C);
title('Image part 3');
subplot 336
imshow(D);
title('Image part 4');