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NAME

        im_contrast_surface,   im_contrast_surface_raw   -  Generate  contrast
       surface

SYNOPSIS

       #include <vips/vips.h>

       int im_contrast_surface( IMAGE *in, IMAGE *out, int half_win_size, int spacing );

       int im_contrast_surface_raw( IMAGE *in, IMAGE *out, int half_win_size, int spacing );

DESCRIPTION

       These functions generate  an  image  where  the  value  of  each  pixel
       represents   the   contrast   within  a  square  window  of  size  2  *
       half_win_size + 1 centred on  the  corresponsing  point  in  the  input
       image.

       The output is sub-sampled by a factor of spacing.

       Input must be single-band uncoded uchar, WIO or PIO.

       Output is single-band uncoded uint, WIO or PIO.

       In  im_contrast_surface(3),  pixels beyond the edges of the input image
       are considered to be have the value of the nearest pixel  which  is  in
       the image.

       Alternatively,    in    im_contrast_surface_raw(3),    pixels    within
       half_win_size of the edge are not calculated,  and  output  is  smaller
       accordingly.

RETURN VALUE

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

COPYRIGHT

       Copyright 2006, The Nottingham Trent University.

AUTHOR

       Tom Vajzovic

                                  01 May 2006