J = imnoise(I,'localvar',IMAGE_INTENSITY,VAR) adds zero-mean, Gaussian
　noise to an image, I, where the local variance of the noise is a
　function of the image intensity values in I.　IMAGE_INTENSITY and VAR
　are vectors of the same size, and PLOT(IMAGE_INTENSITY,VAR) plots the
　functional relationship between noise variance and image intensity.
　IMAGE_INTENSITY must contain normalized intensity values ranging from 0
　to 1.