How do you apply a 3x3 median filter on an image that is noisy (salt and pepper) , and what is it supposed to do?

is this correct?

inpict = imread('Q1_noisy_image (1).tif');
A = medfilt2(inpict,[3 3]); 
imshow(A)

Answer 1

[Image Analyst]

If inpict is a gray scale image, that would apply a median filter to ALL pixels in the image, not just the impulse/salt&pepper noise.

A median filter's claim to fame is that it smooths noisy areas but leaves true edges sharp (it doesn't blur step edges).

If you want a median filter to operate on only salt and pepper noise, you have to

1. First median filter the whole image
2. Get a mask of the salt and papper noise, where values are either 0 or 255 or whatever values you want to use.
3. Replace the original image with the median filtered values but ONLY within the noise mask, not everywhere.

Something like

filteredImage = medfilt2(grayImage, [3,3]);
mask = (grayImage == 0) | (grayImage == 255);
grayImage(mask) = filteredImage(mask);

For a full demo, see my attached demos. For a color image, do it one color channel at a time.

Answer 2

[DGM]

This is the third time you've asked this question. Why?

https://www.mathworks.com/matlabcentral/answers/2055004-i-am-not-sure-if-my-output-is-correct-regarding-median-filters

https://www.mathworks.com/matlabcentral/answers/2054999-i-have-a-salt-and-pepper-picture-and-i-need-to-use-a-median-filter-to-remove-the-noise-and-filter-i

[Hind Aljallaf]

I thought i asked the question wrong, and i want to see what other codes are there to experiment with.

[DGM]

In the future, try to keep things about one question in a common thread so that efforts don't get divided. It's okay to revise your question either by editing it or by using comments.

FWIW, the link I'd provided in 2054999 includes a link to the demos that Image Analyst also posted above.