how to equalize histogram of two images ?

clc

close all

clear all

img1 = imread('img2.jpg');

img2 = imread('img1.jpg');

subplot(3,2,1);

imshow(img1);

title('First Image');

subplot(3,2,2);

imhist(rgb2gray(img1));

title('histogram of First image');

subplot(3,2,3);

imshow(img2);

title('Second Image');

subplot(3,2,4);

imhist(rgb2gray(img2));

title('histogram of Second image');

% how to equalize the histogram of img1 and img2 ? getting error here

a = histeq(rgb2gray(img1,img2));

subplot(3,2,5);

imshow(a);

title('histogram equalize')

% how to equalize the histogram of img1 and img2 ?

Answer 1

[Image Analyst]

You could try imhistmatch(), but as you can see below, it doesn't do such a great job:

testImage = imread('moon.tif');
subplot(2, 3, 1);
imshow(testImage);

refImage = imread('cameraman.tif');
subplot(2, 3, 2);
imshow(refImage);

matchedImage = imhistmatch(testImage, refImage); 
subplot(2, 3, 3);
imshow(matchedImage);

% Plot histograms
subplot(2, 3, 4);
imhist(testImage);
subplot(2, 3, 5);
imhist(refImage);
subplot(2, 3, 6);
imhist(matchedImage);

If you really want to do it right, you have to employ a few tricks (adding noise, sorting, randomly picking, etc.). I employ these tricks in my File Exchange submission which will match any histogram to any other histogram regardless of the shape.

Click for Image Analyst's program

Answer 2

[KALYAN ACHARJYA]

Normally Histogram equalization in one image, I hope you know the objective of hitogram equalization.

If you are trying to do operation on histograms in two images, hopefully it is histogram matching

a=imhistmatch(main_image, referenece_image); 

Please note both are gray images.

In histogram matching, it try to make the histogram of main image as histogram of reference image.

If not, let me know the exact question.