<p>As far as I know these noises are not natural and estimating them is almost impossible. As a simple and handy method, median filter is the best. Since the presence of the noise is too much, the images are corrupted and there is a huge loss in the image information. In this situation, the best practice is to use deep learning method, because they can restore the impaired parts of the image to a desirable level. </p>

<p>I found this paper, promising for such purpose but you would find more resources:</p>

<p><a href="https://arxiv.org/pdf/1810.10039.pdf" rel="nofollow noreferrer">https://arxiv.org/pdf/1810.10039.pdf</a></p>

<p>In this page also you will find many strong deep learning methods and codes for denoising image:</p>

<p><a href="https://github.com/z-bingo/awesome-image-denoising-state-of-the-art" rel="nofollow noreferrer">https://github.com/z-bingo/awesome-image-denoising-state-of-the-art</a></p>
Salt and Pepper impulse Denoising opencv
<p>I am creating a generic method to work on salt and pepper noise and variants. The example images are as shown below :</p>

<p><a href="https://i.stack.imgur.com/qp7qO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qp7qO.png" alt="enter image description here"></a>
<a href="https://i.stack.imgur.com/KthYa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KthYa.png" alt="enter image description here"></a>
<a href="https://i.stack.imgur.com/7qYKc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7qYKc.png" alt="enter image description here"></a></p>

<p>I tried few methods, such as</p>

<ul>
<li>Median filter from scipy</li>
<li>Selective Adaptive Median Filter by Jayanta Das et al.</li>
</ul>

<p>The closest result was on Image 3, with Median filter, giving the closest result to the original image with no noise.</p>

<p>These are my following doubts :</p>

<ol>
<li>Can we consider these noises as salt and pepper noise? Is there something else that I am missing?</li>
<li>What could be the better suggested method? Currently, I am planning to implement Switching Median filter by Pei-Eng et al, but I would like to know if this could be the right track.</li>
</ol>

<p>The originals that I am trying to get closer to:</p>

<p><a href="https://i.stack.imgur.com/lXxDI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lXxDI.png" alt="enter image description here"></a>
<a href="https://i.stack.imgur.com/8GhrU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8GhrU.png" alt="enter image description here"></a>
<a href="https://i.stack.imgur.com/pDzAz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pDzAz.png" alt="enter image description here"></a></p>