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/* creates an butterworth filter.
*
* 02/01/14
* - from butterworth.c
*/
/*
This file is part of VIPS.
VIPS is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA
*/
/*
These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
*/
/*
#define VIPS_DEBUG
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <vips/intl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <vips/vips.h>
#include "pcreate.h"
#include "point.h"
#include "pmask.h"
G_DEFINE_TYPE( VipsMaskButterworth, vips_mask_butterworth,
VIPS_TYPE_MASK );
static double
vips_mask_butterworth_point( VipsMask *mask, double dx, double dy )
{
VipsMaskButterworth *butterworth = (VipsMaskButterworth *) mask;
double order = butterworth->order;
double fc = butterworth->frequency_cutoff;
double ac = butterworth->amplitude_cutoff;
double cnst = (1.0 / ac) - 1.0;
double fc2 = fc * fc;
double dist2 = fc2 / (dx * dx + dy * dy);
return( 1.0 / (1.0 + cnst * pow( dist2, order )) );
}
static void
vips_mask_butterworth_class_init( VipsMaskButterworthClass *class )
{
GObjectClass *gobject_class = G_OBJECT_CLASS( class );
VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
VipsMaskClass *mask_class = VIPS_MASK_CLASS( class );
gobject_class->set_property = vips_object_set_property;
gobject_class->get_property = vips_object_get_property;
vobject_class->nickname = "mask_butterworth";
vobject_class->description = _( "make a butterworth filter" );
mask_class->point = vips_mask_butterworth_point;
VIPS_ARG_DOUBLE( class, "order", 6,
_( "Order" ),
_( "Filter order" ),
VIPS_ARGUMENT_REQUIRED_INPUT,
G_STRUCT_OFFSET( VipsMaskButterworth, order ),
1.0, 1000000.0, 1.0 );
VIPS_ARG_DOUBLE( class, "frequency_cutoff", 7,
_( "Frequency cutoff" ),
_( "Frequency cutoff" ),
VIPS_ARGUMENT_REQUIRED_INPUT,
G_STRUCT_OFFSET( VipsMaskButterworth, frequency_cutoff ),
0.0, 1000000.0, 0.5 );
VIPS_ARG_DOUBLE( class, "amplitude_cutoff", 8,
_( "Amplitude cutoff" ),
_( "Amplitude cutoff" ),
VIPS_ARGUMENT_REQUIRED_INPUT,
G_STRUCT_OFFSET( VipsMaskButterworth, amplitude_cutoff ),
0.0, 1.0, 0.5 );
}
static void
vips_mask_butterworth_init( VipsMaskButterworth *butterworth )
{
butterworth->order = 1.0;
butterworth->frequency_cutoff = 0.5;
butterworth->amplitude_cutoff = 0.5;
}
/**
* vips_mask_butterworth:
* @out: output image
* @width: image size
* @height: image size
* @order: filter order
* @frequency_cutoff: frequency threshold
* @amplitude_cutoff: amplitude threshold
* @...: %NULL-terminated list of optional named arguments
*
* Optional arguments:
*
* * @nodc: don't set the DC pixel
* * @reject: invert the filter sense
* * @optical: coordinates in optical space
* * @uchar: output a uchar image
*
* Make an butterworth high- or low-pass filter, that is, one with a variable,
* smooth transition
* positioned at @frequency_cutoff, where @frequency_cutoff is in
* range 0 - 1. The shape of the curve is controlled by
* @order --- higher values give a sharper transition. See Gonzalez and Wintz,
* Digital Image Processing, 1987.
*
* See also: vips_mask_ideal().
*
* Returns: 0 on success, -1 on error
*/
int
vips_mask_butterworth( VipsImage **out, int width, int height,
double order, double frequency_cutoff, double amplitude_cutoff, ... )
{
va_list ap;
int result;
va_start( ap, amplitude_cutoff );
result = vips_call_split( "mask_butterworth", ap,
out, width, height,
order, frequency_cutoff, amplitude_cutoff );
va_end( ap );
return( result );
}
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