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NAME

       im_maplut - map an image through a lookup table

SYNOPSIS

       #include <vips/vips.h>

       int im_maplut(in, out, lut)
       IMAGE *in, *out, *lut;

DESCRIPTION

       im_maplut()  maps an image through another image, acting as a LUT (Look
       Up Table).  The lut may have any type, and the output image will be  of
       that type.

       The  input image must be an unsigned integer types, that is, it must be
       one of FMTUCHAR, FMTUSHORT or FMTUINT.

       If the input is FMTUCHAR, then the LUT must have 256 elements, in other
       words, lut->Xsize * lut->Ysize == 256.

       If  the input is FMTUSHORT or FMTUINT, then the lut may have any number
       of elements, and input pels whose value is greater  than  lut->Xsize  *
       lut->Ysize  are  mapped  with the last LUT element. The function counts
       and prints the number of image elements which overflow in this way.

       As regards bands, there are three cases:

          - If LUT has one band, then the input may have any number of  bands,
       and
          each band will pass through the same LUT.

          -  If  LUT has the same number of bands as the input, then each band
       of the
          input will be LUTed separately.

          - If the input has one band, then the LUT may  have  any  number  of
       bands, and
          the output will have the same number of bands as the LUT.

RETURN VALUE

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

SEE ALSO

       im_histgr(3), im_hsp(3), im_heq(3), im_identity(3).

COPYRIGHT

       1995, National Gallery and Birkbeck College

AUTHORS

       J. Cupitt, 1995
       N. Dessipris - 10/05/1991

                                  10 May 1991