How to use histogram equalization for a given image, without including the black background ?

Prashant Kumar answered . 2025-07-14 13:48:48

To perform histogram equalization on an image while excluding the black background in MATLAB, you can follow these steps:

1. Read the Image:
   Load the image into MATLAB.

   
   img = imread('yourimage.png');
   

2. Identify Non-Background Pixels:
   Create a mask to identify non-background pixels. Assuming the black background has pixel value 0.

   
   mask = img > 0;
   

3. Apply Histogram Equalization:
   Perform histogram equalization on the non-background pixels.

   
   equalized_img = img;  % Copy the original image
   equalized_img(mask) = histeq(img(mask));
   

4. Display the Result:
   Visualize the original and equalized images.

  
   subplot(1, 2, 1);
   imshow(img);
   title('Original Image');
   
   subplot(1, 2, 2);
   imshow(equalized_img);
   title('Equalized Image');
  

This process enhances the contrast of the image while leaving the black background unchanged.

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