I was asked what I use to create noise profiles. It is ImageJ' a free cross platform Java app from NIH. The best and ad free download site is from NIH-- http://rsbweb.nih.gov/ij/download.html
Once you have it installed open your photo and choose your line type. Drag it across the area of your photo where you want to measure noise. Cntrl+K creates the graph.
To change the Y scale of the graph go to edit, options, plot profile options
For my measurement in the black area of this poster I picked min 0, max 40
Once you have a flat noise profile, go to analyse, measure or hit Cntrl+M
For an accurate noise measurement signal average several. This is a square law thing so 4 measurements doubles your accuracy and 9 measurements triples it. Summarize will do the math where your Signal to Noise (S/N) is the Mean divided by the StdDev (Standard Deviation)
Is this conventional statistical definition of S/N to best way to characterize photographic signal to noise?Probably not. Noise peaks, especially colored noise peaks, that jump out of the average noise are far more distracting than a mild increase in the average noise. So is pattern noise. Both these noise problems will become lost in these numbers. But if you do these comparisons carefully ImageJ is a very useful tool for working out how well the various combinations of sliders and methods work for you.
Final note. You can not save a picture of your graph directly in ImageJ. 'Save as' creates a spread sheet file, 'Clear\' clears out you mistakes and 'Rename' allows you to start a new results list without losing your previous numbers.
Again if you want to know more about noise read Emil's article, http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p2.html