Author: Johannes Schindelin (Johannes.Schindelin at GMX.DE) History: 2006/08/20: First public version
2006/08/29: Add "normalize" checkbox
Limitation: Not trimmed for maximal performance
Source: Included in Two_Point_Correlation.jar. It is based on this paper:
J. G. Berryman and S. C. Blair, Use of digital image analysis to estimate fluid permeability of porous materials I. Application of two-point correlation functions, J. Appl. Phys. 60, 1930-1938 (1986)
Installation: Download Two_Point_Correlation.jar to the plugins folder, or subfolder, restart ImageJ, and there will be a new command in the Plugins menu, "Two Point Correlation". Description: This plugin plots correlation profiles over distances, i.e. for each radius r, the term f(x,y)*f(x',y') is averaged over all x, y, x', y', where the distance between (x, y) and (x', y') is r.
It has two modes, a "naive" one, which carries out the averaging step in a straight-forward fashion, taking a long time but being accurate.
The other mode uses FFT transformations to accelerate the averaging by speeding up the convolution step dramatically, although it is slightly less accurate than the "naive" version.