LOG_MASKS(3) LOG_MASKS(3)
NAME
im_log_dmask, im_log_imask - create a laplacian of gaussian (log) DOU-
BLEMASK or INTMASK
SYNOPSIS
#include <vips/vips.h>
DOUBLEMASK *im_log_dmask( name, sigma, min_amplitude )
char *name;
double sigma, min_amplitude;
INTMASK *im_log_imask( name, sigma, min_amplitude )
char *name;
double sigma, min_amplitude;
DESCRIPTION
Both functions create a circularly symmetric laplacian of Gaussian
mask. The size of the mask is determined by the variable min_ampli-
tude; if for instance the value .1 is entered this means that the pro-
duced mask is clipped at values within 10 persent of zero, and where
the change between mask elements is less than 10%. The mask can be
directly used with the vasari convolution programs, the default offset
set is 0.
The program uses the following equation: (from Handbook of Pattern
Recognition and image processing by Young and Fu, AP 1986 pages
220-221):
H(r) = (1 / (2 * M_PI * s4)) *
(2 - (r2 / s2)) * exp(-r2 / (2 * s2))
where s2 = sigma * sigma, s4=s2 * s2, r2 = r * r. The generated mask
has odd size and its maximum value is normalised to either 100
(log_imask) or to 1.0 (log_dmask)
im_log_dmask() creates a DOUBLEMASK laplacian of Gaussian mask with
maximum value normalised to 1.0.
im_log_imask() creates a INTMASK laplacian of Gaussian mask with maxi-
mum value normalised to 100.
RETURNED VALUE:
The functions return NULL on erorr.
SEE ALSO
im_gauss_dmask(3), im_conv(3)
COPYRIGHT
N. Dessipris
AUTHOR
N. Dessipris - 06/12/1991
6 December 1991 LOG_MASKS(3)
im_log_imask 7.14.5 - Generated Sun Sep 7 18:54:35 CDT 2008