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NAME

       im_gauss_dmask,  im_gauss_imask  -  create  a  gaussian  DOUBLEMASK  or
       INTMASK

SYNOPSIS

       #include <vips/vips.h>

       DOUBLEMASK im_gauss_dmask( name, sigma, min_amplitude )
       char *name;
       double sigma, min_amplitude;

       INTMASK im_gauss_imask( name, sigma, min_amplitude )
       char *name;
       double sigma, min_amplitude;

       INTMASK im_gauss_imask_sep( name, sigma, min_amplitude )
       char *name;
       double sigma, min_amplitude;

DESCRIPTION

       Both functions create a circularly symmetric Gaussian  mask  of  sigma.
       The  size  of  the mask is determined by the variable min_amplitude; if
       for instance the value .1 is entered this means that the produced  mask
       is  clipped  at  values  less than 10 percent of the maximum amplitude.
       The mask can be directly used with the vasari convolution programs, the
       default offset set is 0.

       The program uses the following equation:

          H(r) = exp( -(r * r) / (2 * sigma * sigma) ).

       The  generated mask has odd size and its maximum value is normalised to
       either 100 (gauss_imask) or to 1.0 (gauss_dmask).

       im_gauss_dmask(3) creates a DOUBLEMASK laplacian of Gaussian mask  with
       maximum value normalised to 1.0.

       im_gauss_imask(3)  creates  a  INTMASK  laplacian of Gaussian mask with
       maximum value normalised to 100.

       im_gauss_imask_sep(3) returns the centre line of im_gauss_imask(3).  It
       is  convenient  for  use with im_conv_sep(3) for building fast gaussian
       blur or sharpen.

RETURNED VALUE:

       The functions return NULL on erorr.

SEE ALSO

       im_log_dmask(3), im_conv(3), im_conv_sep(3).

COPYRIGHT

       N. Dessipris

AUTHOR

       N. Dessipris - 06/12/1991

                                6 December 1991                 GAUSS_MASKS(3)