Speckle Size via Autocorrelation

Outputs the size of speckles in an image that has a **uniform background**.

This function takes an RGB image as input and gives the FWHM and 1/e^2 radius of Gaussian-assumed speckles in the horizontal and vertical directions in pixel units.
The function is heavily commented for very easy use, and all mathematical steps are explained in the comments. Briefly, the autocovariance of each row (column) is averaged; the resulting plot is fitted to a Gaussian, from which the horizontal (vertical) FWHM and 1/e^2 values are calculated.
In addition, the function outputs the goodness-of-fit statistics for this Gaussian fit. These should always be checked to ensure proper functioning.