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       im_global_balance, im_global_balancef - perform global mosaic balancing
       on an image


       #include <vips/vips.h>

       im_global_balance( IMAGE *in, IMAGE *out, double gamma )

       im_global_balance_float( IMAGE *in, IMAGE *out, double gamma )


       These functions takes an image assembled with the  mosaicing  functions
       (im_*merge*(),  im_*mosaic*()),  take  it  apart,  and  reassemble  it,
       globally optimising the image balance.  This is useful  for  assembling
       image  mosaics  from sources where the exposure is uncontrolled and may
       vary from tile to tile --- such as video, or photographic sources.

       The function finds a set of factors, one for each of the input  images,
       and  scales  each  image by its factor before reassembling. The factors
       are chosen so as to minimise the average grey-level difference  between
       neighboring  images  at  their  overlaps.   Trivial overlaps (where the
       width and height of the overlap are  both  less  than  20  pixels)  are

       The  gamma parameter is the gamma of the image input system. It is used
       during brightness adjustment. Set to 1.0 to disable gamma, to 1.6 for a
       typical IR vidicon camera, or 2.3 for a typical video camera.

       It  relies  on  information  left by the mosaicing functions in ".desc"
       files. If the ".desc" file of the input image has been corrupted, or is
       strangely complicated, or if any of the original input images have been
       moved or deleted, the function can fail.

       The function will fail for mosaics larger than about  7  by  7  frames,
       since it will run out of file descriptors (UNIX sets a limit of 256 per
       process).  To  balance  larger  mosaics,  just  assemble  them  in  7x7
       sections,  balancing  and  saving  each  part  in turn, before loading,
       assembling and balancing the final image.  The function can  also  fail
       if there are significant mosaicing errors.

       im_global_balancef()  works as im_global_balance(), but outputs a float
       rather than a uchar image. This lets you adjust the range of the  image
       manually, if the automatically-found scales are causing burn-out.


       All functions return 0 on success and -1 on error.


       im_lrmerge(3), im_lrmosaic(3).


       Birkbeck College and the National Gallery, 1991 - 1995.

                                  13 May 1991             IM_GLOBAL_BALANCE(3)