This function calculates the 2D auto correlation function of matrix ( gray scale image) using Wiener-Khinchin theorem and uses the four internal function ifft2,fftshift,fft2 & conj .
In the PDF file "2DAUTOCORRELATIONFUNCTION.pdf" the calculations are detailed using two examples,
1) "circuit.tif" image.
2) 2d zero mean Gaussian signal .
As in 1d, the 2d auto-correlation of the second example is symmetric and has Dirac impulse in the center.