im_heq(3)
NAME
im_heq, im_lhisteq, im_lhisteq_raw, im_hsp - process an image using
grey level transformations
SYNOPSIS
#include <vips/vips.h> int im_heq( in, out, bandno ) IMAGE *in, *out; int bandno; int im_lhisteq( in, out, xw, yw ) IMAGE *in, *out; int xw, yw; int im_hsp( in, ref, out ) IMAGE *in, *ref, *out;
DESCRIPTION
im_heq() histogram equalises the unsigned char image held by the IMAGE
descriptor in. The result is written to the IMAGE descriptor out. If
bandno is -1 then all input bands are equalised independently. In all
other cases the input image is equalised using the histogram of bandno
only. The latter processing produces better results.
im_hsp() maps in to out with histogram specified by the ref. All
images should be unsigned char. Each band of the output image is specified according to the distribution of grey levels of the reference
image according to im_histspec(3).
im_lhisteq() histogram equalises the one channel unsigned char image
pointed to by the Image descriptor in. The result is written to the
IMAGE descriptor out. The histogram equalisation is based on a window
of size xw by yw centered at the current location of each input pixel.
The produced image has a black border of sizes xw/2 (left), xw-xw/2
(right), yw/2 (top) and yw-yw/2 (bottom).
im_lhisteq_raw() is as above, but does not add the black border to the
output image.
RETURN VALUE
All functions returns 0 on success and -1 on error.
SEE ALSO
im_histgr(3), im_histplot(3), im_histspec(3), im_lineprof(3),
im_stdif(3).
COPYRIGHT
- 1991--1996 The National Gallery and Birkbeck College