I'm having troubles trying to use one relatively simple noise estimation method, here it is:A Fast Method For Image Noise Estimation Using Laplacian Operator and Adaptive Edge Detection
My problem is with their proposed noise deviation formula (page $2$, ($3$)), I can't seem to comprehend it. What I want to know am I right that this $N$ is amount of pixels in image?
And also I'm having troubles implementing first part of the formula since its result is float undeflow. Maybe I can just use regular pixel_value - pixel_mean formula? Will it produce same results?
Altrough images with massive noise will have mean that actually pretty much depends on the noise amount and thus estimation will be considerably lower than the real value.
Where can I read about this formula and how to use, or how it's even named?
Maybe I've implemented it wrongly, here's my code that does it: noise deviation implementation (C++ CImg) It gives me very big numbers, like for noisy image of bears I got something like 1830152.
First of all, what I'm supposed to get from that formula? Isn't it supposed to be some kind of 0.xx coefficient or maybe percent of noise in image?