How to identify pixels with noise ?

Hi Everyone, I was wondering if there is any function for detecting (just detecting, not correcting) the number of pixels with noise within an image Take this picture for example :http://imgur.com/VR7bTWV , whose size is 215x215 (or 46,225 pixels). Would it be possible to get the total number of noisy pixels ? i.e 30,000 noisy pixels out of 46,225 total pixels. My idea is to apply noise filtering only if there is a significant amount of noise as noise filtering usually reduces details in the image, also I want to apply different filtering levels based on the existing noise levels . What approach do you suggest ? Thanks in Advance.