AUTO - A COMPUTER-PROGRAM FOR THE DETERMINATION OF THE 2-DIMENSIONAL AUTOCORRELATION FUNCTION OF DIGITAL IMAGES

The two-dimensional (2-D) autocorrelation function (ACF) of an image s tatistically characterizes the spatial pattern within that image and p resents a powerful tool for fabric analysis. It determines shape prefe rred orientation, degree of alignment, and distribution anisotropy of image objects. We present here a fast, user-friendly, MS-DOS based com puter program, AUTO, to calculate the 2-D ACF of a digital monochrome image. AUTO displays an image on the screen and allows selection of a portion of the image for autocorrelation. Rapid calculation of ACF val ues is achieved by using a fast Fourier transform (FFT) routine accord ing to the convolution theorem. The spatial distribution of ACF values is contoured for quantitative analysis of fabric anisotropy. Applicat ions of this technique include the determination of grain or pore fabr ic of geological specimens, strain analysis, and the interpretation of petrophysical properties.