| .TH LOG_MASKS 3 "6 December 1991" |
| .SH NAME |
| im_log_dmask, im_log_imask \- create a laplacian of gaussian (log) |
| DOUBLEMASK or INTMASK |
| .SH SYNOPSIS |
| .B |
| #include <vips/vips.h> |
| |
| |
| .B DOUBLEMASK *im_log_dmask( name, sigma, min_amplitude ) |
| .br |
| char *name; |
| .br |
| double sigma, min_amplitude; |
| |
| .B INTMASK *im_log_imask( name, sigma, min_amplitude ) |
| .br |
| char *name; |
| .br |
| double sigma, min_amplitude; |
| .SH DESCRIPTION |
| Both functions create a circularly symmetric laplacian of Gaussian mask. 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 |
| 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) |
| |
| .B im_log_dmask() |
| creates a DOUBLEMASK laplacian of Gaussian mask with maximum value normalised |
| to 1.0. |
| |
| .B im_log_imask() |
| creates a INTMASK laplacian of Gaussian mask with maximum value normalised |
| to 100. |
| .SH RETURNED VALUE: |
| The functions return NULL on erorr. |
| .SH SEE ALSO |
| im_gauss_dmask(3), im_conv(3) |
| .SH COPYRIGHT |
| .br |
| N. Dessipris |
| .SH AUTHOR |
| N. Dessipris \- 06/12/1991 |
