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libvips/libvips/convolution/convasep.c

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/* convasep ... separable approximate convolution
*
* This operation does an approximate, seperable convolution.
*
* Author: John Cupitt & Nicolas Robidoux
* Written on: 31/5/11
* Modified on:
* 31/5/11
* - from im_conv()
* 5/7/16
* - redone as a class
*/
/*
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
*/
/*
See:
http://incubator.quasimondo.com/processing/stackblur.pde
This thing is a little like stackblur, but generalised to any separable
mask.
*/
/*
TODO
- are we handling mask offset correctly?
nope! we have area and rounding, but neither properly incorporates
offset
- how about making a cumulative image and then subtracting points in
that, rather than keeping a set of running totals
faster?
we could then use orc to write a bit of code to implement this set
of lines
*/
/* Show sample pixels as they are transformed.
#define DEBUG_PIXELS
*/
/*
#define DEBUG
#define VIPS_DEBUG
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <vips/intl.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <math.h>
#include <vips/vips.h>
#include <vips/vector.h>
#include <vips/debug.h>
#include <vips/internal.h>
#include "pconvolution.h"
/* Maximum number of lines we can break the mask into.
*/
#define MAX_LINES (1000)
/* Euclid's algorithm. Use this to common up mults.
*/
static int
gcd( int a, int b )
{
if( b == 0 )
return( abs( a ) );
else
return( gcd( b, a % b ) );
}
typedef struct {
VipsConvolution parent_instance;
int layers;
int area;
int rounding;
int offset;
/* The "width" of the mask, ie. n for our 1xn or nx1 argument, plus
* an int version of our mask.
*/
int width;
VipsImage *iM;
/* The mask broken into a set of lines.
*
* Start is the left-most pixel in the line, end is one beyond the
* right-most pixel.
*/
int n_lines;
int start[MAX_LINES];
int end[MAX_LINES];
int factor[MAX_LINES];
} VipsConvasep;
typedef VipsConvolutionClass VipsConvasepClass;
G_DEFINE_TYPE( VipsConvasep, vips_convasep, VIPS_TYPE_CONVOLUTION );
static void
vips_convasep_line_start( VipsConvasep *convasep, int x, int factor )
{
convasep->start[convasep->n_lines] = x;
convasep->factor[convasep->n_lines] = factor;
}
static int
vips_convasep_line_end( VipsConvasep *convasep, int x )
{
VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( convasep );
convasep->end[convasep->n_lines] = x;
if( convasep->n_lines >= MAX_LINES - 1 ) {
vips_error( class->nickname, "%s", _( "mask too complex" ) );
return( -1 );
}
convasep->n_lines += 1;
return( 0 );
}
/* Break a mask into lines.
*/
static int
vips_convasep_decompose( VipsConvasep *convasep )
{
VipsImage *iM = convasep->iM;
double *coeff = (double *) VIPS_IMAGE_ADDR( iM, 0, 0 );
double scale = vips_image_get_scale( iM );
double offset = vips_image_get_offset( iM );
double max;
double min;
double depth;
double sum;
int layers;
int layers_above;
int layers_below;
int z, n, x;
VIPS_DEBUG_MSG( "vips_convasep_decompose: "
"breaking into %d layers ...\n", convasep->layers );
/* Find mask range. We must always include the zero axis in the mask.
*/
max = 0;
min = 0;
for( x = 0; x < convasep->width; x++ ) {
if( coeff[x] > max )
max = coeff[x];
if( coeff[x] < min )
min = coeff[x];
}
/* The zero axis must fall on a layer boundary. Estimate the
* depth, find n-lines-above-zero, get exact depth, then calculate a
* fixed n-lines which includes any negative parts.
*/
depth = (max - min) / convasep->layers;
layers_above = ceil( max / depth );
depth = max / layers_above;
layers_below = floor( min / depth );
layers = layers_above - layers_below;
VIPS_DEBUG_MSG( "depth = %g, layers = %d\n", depth, layers );
/* For each layer, generate a set of lines which are inside the
* perimeter. Work down from the top.
*/
for( z = 0; z < layers; z++ ) {
double y = max - (1 + z) * depth;
/* y plus half depth ... ie. the layer midpoint.
*/
double y_ph = y + depth / 2;
/* Odd, but we must avoid rounding errors that make us miss 0
* in the line above.
*/
int y_positive = z < layers_above;
int inside;
/* Start outside the perimeter.
*/
inside = 0;
for( x = 0; x < convasep->width; x++ ) {
/* The vertical line from mask[z] to 0 is inside. Is
* our current square (x, y) part of that line?
*/
if( (y_positive && coeff[x] >= y_ph) ||
(!y_positive && coeff[x] <= y_ph) ) {
if( !inside ) {
vips_convasep_line_start( convasep, x,
y_positive ? 1 : -1 );
inside = 1;
}
}
else if( inside ) {
if( vips_convasep_line_end( convasep, x ) )
return( -1 );
inside = 0;
}
}
if( inside &&
vips_convasep_line_end( convasep, convasep->width ) )
return( -1 );
}
/* Can we common up any lines? Search for lines with identical
* start/end.
*/
for( z = 0; z < convasep->n_lines; z++ ) {
for( n = z + 1; n < convasep->n_lines; n++ ) {
if( convasep->start[z] == convasep->start[n] &&
convasep->end[z] == convasep->end[n] ) {
convasep->factor[z] += convasep->factor[n];
/* n can be deleted. Do this in a separate
* pass below.
*/
convasep->factor[n] = 0;
}
}
}
/* Now we can remove all factor 0 lines.
*/
for( z = 0; z < convasep->n_lines; z++ ) {
if( convasep->factor[z] == 0 ) {
for( x = z; x < convasep->n_lines; x++ ) {
convasep->start[x] = convasep->start[x + 1];
convasep->end[x] = convasep->end[x + 1];
convasep->factor[x] = convasep->factor[x + 1];
}
convasep->n_lines -= 1;
}
}
/* Find the area of the lines.
*/
convasep->area = 0;
for( z = 0; z < convasep->n_lines; z++ )
convasep->area += convasep->factor[z] *
(convasep->end[z] - convasep->start[z]);
/* Strength reduction: if all lines are divisible by n, we can move
* that n out into the ->area factor. The aim is to produce as many
* factor 1 lines as we can and to reduce the chance of overflow.
*/
x = convasep->factor[0];
for( z = 1; z < convasep->n_lines; z++ )
x = gcd( x, convasep->factor[z] );
for( z = 0; z < convasep->n_lines; z++ )
convasep->factor[z] /= x;
convasep->area *= x;
/* Find the area of the original mask.
*/
sum = 0;
for( z = 0; z < convasep->width; z++ )
sum += coeff[z];
convasep->area = rint( sum * convasep->area / scale );
convasep->rounding = (convasep->area + 1) / 2;
convasep->offset = offset;
#ifdef DEBUG
/* ASCII-art layer drawing.
*/
printf( "lines:\n" );
for( z = 0; z < convasep->n_lines; z++ ) {
printf( "%3d - %2d x ", z, convasep->factor[z] );
for( x = 0; x < 55; x++ ) {
int rx = x * (convasep->width + 1) / 55;
if( rx >= convasep->start[z] && rx < convasep->end[z] )
printf( "#" );
else
printf( " " );
}
printf( " %3d .. %3d\n", convasep->start[z], convasep->end[z] );
}
printf( "area = %d\n", convasep->area );
printf( "rounding = %d\n", convasep->rounding );
printf( "offset = %d\n", convasep->offset );
#endif /*DEBUG*/
return( 0 );
}
/* Our sequence value.
*/
typedef struct {
VipsConvasep *convasep;
VipsRegion *ir; /* Input region */
int *start; /* Offsets for start and stop */
int *end;
/* The sums for each line. int for integer types, double for floating
* point types.
*/
int *isum;
double *dsum;
int last_stride; /* Avoid recalcing offsets, if we can */
} VipsConvasepSeq;
/* Free a sequence value.
*/
static int
vips_convasep_stop( void *vseq, void *a, void *b )
{
VipsConvasepSeq *seq = (VipsConvasepSeq *) vseq;
VIPS_UNREF( seq->ir );
VIPS_FREE( seq->start );
VIPS_FREE( seq->end );
VIPS_FREE( seq->isum );
VIPS_FREE( seq->dsum );
return( 0 );
}
/* Convolution start function.
*/
static void *
vips_convasep_start( VipsImage *out, void *a, void *b )
{
VipsImage *in = (IMAGE *) a;
VipsConvasep *convasep = (VipsConvasep *) b;
VipsConvasepSeq *seq;
if( !(seq = VIPS_NEW( out, VipsConvasepSeq )) )
return( NULL );
/* Init!
*/
seq->convasep = convasep;
seq->ir = vips_region_new( in );
seq->start = VIPS_ARRAY( NULL, convasep->n_lines, int );
seq->end = VIPS_ARRAY( NULL, convasep->n_lines, int );
seq->isum = NULL;
seq->dsum = NULL;
if( vips_band_format_isint( out->BandFmt ) )
seq->isum = VIPS_ARRAY( NULL, convasep->n_lines, int );
else
seq->dsum = VIPS_ARRAY( NULL, convasep->n_lines, double );
seq->last_stride = -1;
if( !seq->ir ||
!seq->start ||
!seq->end ||
(!seq->isum && !seq->dsum) ) {
vips_convasep_stop( seq, in, convasep );
return( NULL );
}
return( seq );
}
#define CLIP_UCHAR( V ) \
G_STMT_START { \
if( (V) < 0 ) \
(V) = 0; \
else if( (V) > UCHAR_MAX ) \
(V) = UCHAR_MAX; \
} G_STMT_END
#define CLIP_CHAR( V ) \
G_STMT_START { \
if( (V) < SCHAR_MIN ) \
(V) = SCHAR_MIN; \
else if( (V) > SCHAR_MAX ) \
(V) = SCHAR_MAX; \
} G_STMT_END
#define CLIP_USHORT( V ) \
G_STMT_START { \
if( (V) < 0 ) \
(V) = 0; \
else if( (V) > USHRT_MAX ) \
(V) = USHRT_MAX; \
} G_STMT_END
#define CLIP_SHORT( V ) \
G_STMT_START { \
if( (V) < SHRT_MIN ) \
(V) = SHRT_MIN; \
else if( (V) > SHRT_MAX ) \
(V) = SHRT_MAX; \
} G_STMT_END
#define CLIP_NONE( V ) {}
/* The h and v loops are very similar, but also annoyingly different. Keep
* them separate for easy debugging.
*/
#define HCONV_INT( TYPE, CLIP ) { \
for( i = 0; i < bands; i++ ) { \
int *isum = seq->isum; \
\
TYPE *q; \
TYPE *p; \
int sum; \
\
p = i + (TYPE *) VIPS_REGION_ADDR( ir, r->left, r->top + y ); \
q = i + (TYPE *) VIPS_REGION_ADDR( or, r->left, r->top + y ); \
\
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
isum[z] = 0; \
for( x = seq->start[z]; x < seq->end[z]; x += istride ) \
isum[z] += p[x]; \
sum += convasep->factor[z] * isum[z]; \
} \
sum = (sum + convasep->rounding) / convasep->area + \
convasep->offset; \
CLIP( sum ); \
*q = sum; \
q += ostride; \
\
for( x = 1; x < r->width; x++ ) { \
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
isum[z] += p[seq->end[z]]; \
isum[z] -= p[seq->start[z]]; \
sum += convasep->factor[z] * isum[z]; \
} \
p += istride; \
sum = (sum + convasep->rounding) / convasep->area + \
convasep->offset; \
CLIP( sum ); \
*q = sum; \
q += ostride; \
} \
} \
}
#define HCONV_FLOAT( TYPE ) { \
for( i = 0; i < bands; i++ ) { \
double *dsum = seq->dsum; \
\
TYPE *q; \
TYPE *p; \
double sum; \
\
p = i + (TYPE *) VIPS_REGION_ADDR( ir, r->left, r->top + y ); \
q = i + (TYPE *) VIPS_REGION_ADDR( or, r->left, r->top + y ); \
\
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
dsum[z] = 0; \
for( x = seq->start[z]; x < seq->end[z]; x += istride ) \
dsum[z] += p[x]; \
sum += convasep->factor[z] * dsum[z]; \
} \
sum = sum / convasep->area + convasep->offset; \
*q = sum; \
q += ostride; \
\
for( x = 1; x < r->width; x++ ) { \
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
dsum[z] += p[seq->end[z]]; \
dsum[z] -= p[seq->start[z]]; \
sum += convasep->factor[z] * dsum[z]; \
} \
p += istride; \
sum = sum / convasep->area + convasep->offset; \
*q = sum; \
q += ostride; \
} \
} \
}
/* Do horizontal masks ... we scan the mask along scanlines.
*/
static int
vips_convasep_generate_horizontal( VipsRegion *or,
void *vseq, void *a, void *b, gboolean *stop )
{
VipsConvasepSeq *seq = (VipsConvasepSeq *) vseq;
VipsImage *in = (VipsImage *) a;
VipsConvasep *convasep = (VipsConvasep *) b;
VipsConvolution *convolution = (VipsConvolution *) convasep;
VipsRegion *ir = seq->ir;
const int n_lines = convasep->n_lines;
VipsRect *r = &or->valid;
/* Double the bands (notionally) for complex.
*/
int bands = vips_band_format_iscomplex( in->BandFmt ) ?
2 * in->Bands : in->Bands;
VipsRect s;
int x, y, z, i;
int istride;
int ostride;
/* Prepare the section of the input image we need. A little larger
* than the section of the output image we are producing.
*/
s = *r;
s.width += convasep->width - 1;
if( vips_region_prepare( ir, &s ) )
return( -1 );
/* Stride can be different for the vertical case, keep this here for
* ease of direction change.
*/
istride = VIPS_IMAGE_SIZEOF_PEL( in ) /
VIPS_IMAGE_SIZEOF_ELEMENT( in );
ostride = VIPS_IMAGE_SIZEOF_PEL( convolution->out ) /
VIPS_IMAGE_SIZEOF_ELEMENT( convolution->out );
/* Init offset array.
*/
if( seq->last_stride != istride ) {
seq->last_stride = istride;
for( z = 0; z < n_lines; z++ ) {
seq->start[z] = convasep->start[z] * istride;
seq->end[z] = convasep->end[z] * istride;
}
}
for( y = 0; y < r->height; y++ ) {
switch( in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
HCONV_INT( unsigned char, CLIP_UCHAR );
break;
case VIPS_FORMAT_CHAR:
HCONV_INT( signed char, CLIP_CHAR );
break;
case VIPS_FORMAT_USHORT:
HCONV_INT( unsigned short, CLIP_USHORT );
break;
case VIPS_FORMAT_SHORT:
HCONV_INT( signed short, CLIP_SHORT );
break;
case VIPS_FORMAT_UINT:
HCONV_INT( unsigned int, CLIP_NONE );
break;
case VIPS_FORMAT_INT:
HCONV_INT( signed int, CLIP_NONE );
break;
case VIPS_FORMAT_FLOAT:
case VIPS_FORMAT_COMPLEX:
HCONV_FLOAT( float );
break;
case VIPS_FORMAT_DOUBLE:
case VIPS_FORMAT_DPCOMPLEX:
HCONV_FLOAT( double );
break;
default:
g_assert_not_reached();
}
}
return( 0 );
}
#define VCONV_INT( TYPE, CLIP ) { \
for( x = 0; x < sz; x++ ) { \
int *isum = seq->isum; \
\
TYPE *q; \
TYPE *p; \
int sum; \
\
p = x + (TYPE *) VIPS_REGION_ADDR( ir, r->left, r->top ); \
q = x + (TYPE *) VIPS_REGION_ADDR( or, r->left, r->top ); \
\
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
isum[z] = 0; \
for( y = seq->start[z]; y < seq->end[z]; y += istride ) \
isum[z] += p[y]; \
sum += convasep->factor[z] * isum[z]; \
} \
sum = (sum + convasep->rounding) / convasep->area + \
convasep->offset; \
CLIP( sum ); \
*q = sum; \
q += ostride; \
\
for( y = 1; y < r->height; y++ ) { \
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
isum[z] += p[seq->end[z]]; \
isum[z] -= p[seq->start[z]]; \
sum += convasep->factor[z] * isum[z]; \
} \
p += istride; \
sum = (sum + convasep->rounding) / convasep->area + \
convasep->offset; \
CLIP( sum ); \
*q = sum; \
q += ostride; \
} \
} \
}
#define VCONV_FLOAT( TYPE ) { \
for( x = 0; x < sz; x++ ) { \
double *dsum = seq->dsum; \
\
TYPE *q; \
TYPE *p; \
double sum; \
\
p = x + (TYPE *) VIPS_REGION_ADDR( ir, r->left, r->top ); \
q = x + (TYPE *) VIPS_REGION_ADDR( or, r->left, r->top ); \
\
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
dsum[z] = 0; \
for( y = seq->start[z]; y < seq->end[z]; y += istride ) \
dsum[z] += p[y]; \
sum += convasep->factor[z] * dsum[z]; \
} \
sum = sum / convasep->area + convasep->offset; \
*q = sum; \
q += ostride; \
\
for( y = 1; y < r->height; y++ ) { \
sum = 0; \
for( z = 0; z < n_lines; z++ ) { \
dsum[z] += p[seq->end[z]]; \
dsum[z] -= p[seq->start[z]]; \
sum += convasep->factor[z] * dsum[z]; \
} \
p += istride; \
sum = sum / convasep->area + convasep->offset; \
*q = sum; \
q += ostride; \
} \
} \
}
/* Do vertical masks ... we scan the mask down columns of pixels. Copy-paste
* from above with small changes.
*/
static int
vips_convasep_generate_vertical( VipsRegion *or,
void *vseq, void *a, void *b, gboolean *stop )
{
VipsConvasepSeq *seq = (VipsConvasepSeq *) vseq;
VipsImage *in = (VipsImage *) a;
VipsConvasep *convasep = (VipsConvasep *) b;
VipsConvolution *convolution = (VipsConvolution *) convasep;
VipsRegion *ir = seq->ir;
const int n_lines = convasep->n_lines;
VipsRect *r = &or->valid;
/* Double the width (notionally) for complex.
*/
int sz = vips_band_format_iscomplex( in->BandFmt ) ?
2 * VIPS_REGION_N_ELEMENTS( or ) : VIPS_REGION_N_ELEMENTS( or );
VipsRect s;
int x, y, z;
int istride;
int ostride;
/* Prepare the section of the input image we need. A little larger
* than the section of the output image we are producing.
*/
s = *r;
s.height += convasep->width - 1;
if( vips_region_prepare( ir, &s ) )
return( -1 );
/* Stride can be different for the vertical case, keep this here for
* ease of direction change.
*/
istride = VIPS_REGION_LSKIP( ir ) / VIPS_IMAGE_SIZEOF_ELEMENT( in );
ostride = VIPS_REGION_LSKIP( or ) /
VIPS_IMAGE_SIZEOF_ELEMENT( convolution->out );
/* Init offset array.
*/
if( seq->last_stride != istride ) {
seq->last_stride = istride;
for( z = 0; z < n_lines; z++ ) {
seq->start[z] = convasep->start[z] * istride;
seq->end[z] = convasep->end[z] * istride;
}
}
switch( in->BandFmt ) {
case VIPS_FORMAT_UCHAR:
VCONV_INT( unsigned char, CLIP_UCHAR );
break;
case VIPS_FORMAT_CHAR:
VCONV_INT( signed char, CLIP_CHAR );
break;
case VIPS_FORMAT_USHORT:
VCONV_INT( unsigned short, CLIP_USHORT );
break;
case VIPS_FORMAT_SHORT:
VCONV_INT( signed short, CLIP_SHORT );
break;
case VIPS_FORMAT_UINT:
VCONV_INT( unsigned int, CLIP_NONE );
break;
case VIPS_FORMAT_INT:
VCONV_INT( signed int, CLIP_NONE );
break;
case VIPS_FORMAT_FLOAT:
case VIPS_FORMAT_COMPLEX:
VCONV_FLOAT( float );
break;
case VIPS_FORMAT_DOUBLE:
case VIPS_FORMAT_DPCOMPLEX:
VCONV_FLOAT( double );
break;
default:
g_assert_not_reached();
}
return( 0 );
}
static int
vips_convasep_pass( VipsConvasep *convasep,
VipsImage *in, VipsImage **out, VipsDirection direction )
{
VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( convasep );
VipsGenerateFn gen;
*out = vips_image_new();
if( vips_image_pipelinev( *out,
VIPS_DEMAND_STYLE_SMALLTILE, in, NULL ) )
return( -1 );
if( direction == VIPS_DIRECTION_HORIZONTAL ) {
(*out)->Xsize -= convasep->width - 1;
gen = vips_convasep_generate_horizontal;
}
else {
(*out)->Ysize -= convasep->width - 1;
gen = vips_convasep_generate_vertical;
}
if( (*out)->Xsize <= 0 ||
(*out)->Ysize <= 0 ) {
vips_error( class->nickname,
"%s", _( "image too small for mask" ) );
return( -1 );
}
if( vips_image_generate( *out,
vips_convasep_start, gen, vips_convasep_stop, in, convasep ) )
return( -1 );
return( 0 );
}
static int
vips_convasep_build( VipsObject *object )
{
VipsConvolution *convolution = (VipsConvolution *) object;
VipsConvasep *convasep = (VipsConvasep *) object;
VipsImage **t = (VipsImage **) vips_object_local_array( object, 4 );
VipsImage *in;
if( VIPS_OBJECT_CLASS( vips_convasep_parent_class )->build( object ) )
return( -1 );
/* An int version of our mask.
*/
if( vips__image_intize( convolution->M, &t[3] ) )
return( -1 );
convasep->iM = t[3];
convasep->width = convasep->iM->Xsize * convasep->iM->Ysize;
in = convolution->in;
if( vips_convasep_decompose( convasep ) )
return( -1 );
g_object_set( convasep, "out", vips_image_new(), NULL );
if(
vips_embed( in, &t[0],
convasep->width / 2,
convasep->width / 2,
in->Xsize + convasep->width - 1,
in->Ysize + convasep->width - 1,
"extend", VIPS_EXTEND_COPY,
NULL ) ||
vips_convasep_pass( convasep,
t[0], &t[1], VIPS_DIRECTION_HORIZONTAL ) ||
vips_convasep_pass( convasep,
t[1], &t[2], VIPS_DIRECTION_VERTICAL ) ||
vips_image_write( t[2], convolution->out ) )
return( -1 );
convolution->out->Xoffset = 0;
convolution->out->Yoffset = 0;
return( 0 );
}
static void
vips_convasep_class_init( VipsConvasepClass *class )
{
GObjectClass *gobject_class = G_OBJECT_CLASS( class );
VipsObjectClass *object_class = (VipsObjectClass *) class;
gobject_class->set_property = vips_object_set_property;
gobject_class->get_property = vips_object_get_property;
object_class->nickname = "convasep";
object_class->description = _( "approximate separable convolution" );
object_class->build = vips_convasep_build;
VIPS_ARG_INT( class, "layers", 104,
_( "Layers" ),
_( "Use this many layers in approximation" ),
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsConvasep, layers ),
1, 1000, 5 );
}
static void
vips_convasep_init( VipsConvasep *convasep )
{
convasep->layers = 5;
convasep->n_lines = 0;
}
/**
* vips_convasep:
* @in: input image
* @out: output image
* @mask: convolve with this mask
* @...: %NULL-terminated list of optional named arguments
*
* Optional arguments:
*
* * @layers: %gint, number of layers for approximation
*
* Approximate separable convolution. This is a low-level operation, see
* vips_convsep() for something more convenient.
*
* The mask must be 1xn or nx1 elements.
* The output image
* always has the same #VipsBandFormat as the input image.
*
* The image is convolved twice: once with @mask and then again with @mask
* rotated by 90 degrees.
*
* Larger values for @layers give more accurate
* results, but are slower. As @layers approaches the mask radius, the
* accuracy will become close to exact convolution and the speed will drop to
* match. For many large masks, such as Gaussian, @layers need be only 10% of
* this value and accuracy will still be good.
*
* See also: vips_conv().
*
* Returns: 0 on success, -1 on error
*/
int
vips_convasep( VipsImage *in, VipsImage **out, VipsImage *mask, ... )
{
va_list ap;
int result;
va_start( ap, mask );
result = vips_call_split( "convasep", ap, in, out, mask );
va_end( ap );
return( result );
}
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