How to add noise to intensity image to get lower SNR?

I have an instensity image with 3 regions (shadow(blue), object(yellow) and background(waves)). Now I need to increase noise to the shadow and object regions so that we are unable to identify regions clearly. That is, I need check the limit of SNR value. How can I find the SNR limit value? What parameters I have to change?

Answer 1

[Image Analyst]

I don't know your definition of "SNR limit value" but to change the noise only in some particular region you can use indexing:

B(row1:row2, col1:col2) = noiseImage; % Assign a noisy image to specified region.

You would make up noiseImage in advance with the exact number of rows and columns as the region you want to put it into.

[kumara dommeti]

I want to increase variance to increase the noise in the image. So that SNR will decrease in that particular region. (I dont want to replace).

[Image Analyst]

OK, yep, what I said should work.