.TH IM_MEASURE 3 "24 October 1992"
.SH NAME
im_measure \- measure colour patches off images
.SH SYNOPSIS
#include <vips/vips.h>

DOUBLEMASK *im_measure(in, box, h, v, sel, nsel, name)
.br
IMAGE *in;
.br
IMAGE_BOX *box;
.br
int h, v;
.br
int *sel;
.br
int nsel;
.br
char *name;

.SH DESCRIPTION
Analyse a grid of colour patches, producing a DOUBLEMASK of averages.
Pass an IMAGE, an IMAGE_BOX, the number of horizontal and vertical
patches, an array giving the numbers of the patches to measure (patches
are numbered left-to-right, top-to-bottom, starting with 1) and the name we
should give the output mask. Return a DOUBLEMASK in which rows are patches and
columns are bands. Only the central 50% of each patch is averaged.

Example: 6 band image of 4x2 block of colour patches.
 
 +---+---+---+---+
 | 1 | 2 | 3 | 4 |
 +---+---+---+---+
 | 5 | 6 | 7 | 8 |
 +---+---+---+---+

Then call im_measure( im, box, 4, 2, { 2, 4 }, 2, "fred" ) makes a mask
"fred" which has 6 columns, two rows. The first row contains the averages
for patch 2, the second for patch 4.

Output warnings: a warning is issued if the standard deviation of any patch is
greater than 20% of the mean of that patch.

.SH RETURN VALUE
NULL on error.
.SH SEE ALSO
im_avg(3), im_deviate(3), im_stats(3).