IM_FASTCOR

Section: C Library Functions (3)
Updated: 14 May 1991
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NAME

im_fastcor, im_spcor - correlate two images

SYNOPSIS

#include <vips/vips.h>

int im_fastcor(in, ref, out)
IMAGE *in, *ref, *out;

int im_spcor(in, ref, out)
IMAGE *in, *ref, *out;

DESCRIPTION

These functions calculate spatial correlation between two one-band images held by the image descriptors in and ref. The sizes of ref should be smaller than the sizes of in. The correlation is carried out by overlapping ref on the top left corner of in and moving it over in.

The output image is the same size as the input. The edge pixels are calculated by expanding the input image using im_embed(3) in mode 1 (replicating edge pixels) just enough so that the output can match the input.

im_spcor(3) calculates the spatial correlation between in and ref using the correlation coefficient from Niblack "An Introduction to Digital Image Processing,", Prentice/Hall, pp 138. The resultant coefficients are written as float numbers in out. The images must be char, short or ushort.

im_fastcor(3) simply returns the sum of squares of differences between in and ref. This is much faster, but less useful. The resultant coefficients are written as unsigned int numbers in out which has a size of in.

BUGS

The functions do not check for integer overflow.

RETURN VALUE

The function returns 0 on success and -1 on error.

COPYRIGHT

The National Gallery and Birkbeck College, 1990-1997.