It helps to visualize the data in a different way than a two dimensional plane of pixels of varying values, too. A histogram is a way of representing the information based on the frequency at which pixels of certain values are found. The histogram is, in effect, a plot of the distribution...such as the gaussian or poisson distribution...of the data:

One standard deviation is represented by the dark blue band to one side of the mean...which in this case, of a normal (gaussian) distribution, is dead-center of the distribution. Two standard deviations extends into the lighter blue, and three standard deviations extends into the lightest blue. To one side, one standard deviation represents (in a normal distribution) ~34% of the samples (pixels). To both sides, it represents ~68%. Two standard deviations represents ~95%, and three standard deviations represents over 99%. Strong signals will tend towards a normal distribution in their nature. So, if you know what a standard deviation is, you can understand a lot about your signal.

**Edited by Jon Rista, 17 September 2019 - 11:08 PM.**