How to calculate noise in image

How to calculate noise in image I am using a gray image

Answer 1

[Lokesh]

It is my understanding that you would want to calculate noise in a gray image.

The function estimate_noise inputs a grayscale image I and returns Sigma, the noise estimate. Here is a sample use:

I = rgb2gray(imread('sample.jpg')); ( can be skipped when input image is gray)

Sigma=estimate_noise(I);

Refer to this link for more details:

https://in.mathworks.com/matlabcentral/fileexchange/36941-fast-noise-estimation-in-images