1LOG_MASKS(3)               Library Functions Manual               LOG_MASKS(3)
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NAME

6       im_log_dmask,  im_log_imask - create a laplacian of gaussian (log) DOU‐
7       BLEMASK or INTMASK
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SYNOPSIS

10       #include <vips/vips.h>
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13       DOUBLEMASK *im_log_dmask( name, sigma, min_amplitude )
14       char *name;
15       double sigma, min_amplitude;
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17       INTMASK *im_log_imask( name, sigma, min_amplitude )
18       char *name;
19       double sigma, min_amplitude;
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DESCRIPTION

22       Both functions create a  circularly  symmetric  laplacian  of  Gaussian
23       mask.   The  size  of the mask is determined by the variable min_ampli‐
24       tude; if for instance the value .1 is entered this means that the  pro‐
25       duced  mask  is  clipped at values within 10 persent of zero, and where
26       the change between mask elements is less than 10%.   The  mask  can  be
27       directly  used with the vasari convolution programs, the default offset
28       set is 0.
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30       The program uses the following  equation:  (from  Handbook  of  Pattern
31       Recognition  and  image  processing  by  Young  and  Fu,  AP 1986 pages
32       220-221):
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34         H(r) = (1 / (2 * M_PI * s4)) *
35                (2 - (r2 / s2)) *       exp(-r2 / (2 * s2))
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37       where s2 = sigma * sigma, s4=s2 * s2, r2 = r * r.  The  generated  mask
38       has  odd  size  and  its  maximum  value  is  normalised  to either 100
39       (log_imask) or to 1.0 (log_dmask)
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41       im_log_dmask() creates a DOUBLEMASK laplacian  of  Gaussian  mask  with
42       maximum value normalised to 1.0.
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44       im_log_imask()  creates a INTMASK laplacian of Gaussian mask with maxi‐
45       mum value normalised to 100.
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RETURNED VALUE:

48       The functions return NULL on erorr.
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SEE ALSO

51       im_gauss_dmask(3), im_conv(3)
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54       N. Dessipris
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AUTHOR

57       N. Dessipris - 06/12/1991
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61                                6 December 1991                   LOG_MASKS(3)
Impressum