| .TH IM_FASTCOR 3 "14 May 1991" |
| .SH NAME |
| im_fastcor, im_spcor \- correlate two images |
| .SH SYNOPSIS |
| .B #include <vips/vips.h> |
| |
| .B int im_fastcor(in, ref, out) |
| .br |
| .B IMAGE *in, *ref, *out; |
| |
| .B int im_spcor(in, ref, out) |
| .br |
| .B IMAGE *in, *ref, *out; |
| .SH DESCRIPTION |
| These functions calculate spatial correlation between two |
| one-band images held |
| by the image descriptors |
| .B in |
| and |
| .B ref. |
| The sizes of |
| .B ref |
| should be smaller than |
| the sizes of |
| .B in. |
| The correlation is carried out by overlapping |
| .B ref |
| on the top |
| left corner of |
| .B in |
| and moving it over |
| .B in. |
| |
| The output image is the same size as the input. The edge pixels are calculated |
| by expanding the input image using |
| .B im_embed(3) |
| in mode 1 (replicating edge pixels) just enough so that the output can match |
| the input. |
| |
| .B im_spcor(3) |
| calculates the spatial correlation between |
| .B in |
| and |
| .B 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 |
| .B out. |
| The images must be char, short or ushort. |
| |
| .B im_fastcor(3) |
| simply returns the sum of squares of differences between |
| .B in |
| and |
| .B 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. |
| |
| .SH BUGS |
| The functions do not check for integer overflow. |
| .SH RETURN VALUE |
| The function returns 0 on success and -1 on error. |
| .SH SEE ALSO |
| im_conv(3), im_lrmosaic(3). |
| .SH COPYRIGHT |
| The National Gallery and Birkbeck College, 1990-1997. |
