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       im_measure - measure colour patches off images


       #include <vips/vips.h>

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


       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.


       NULL on error.


       im_avg(3), im_deviate(3), im_stats(3).

                                24 October 1992