515 lines
12 KiB
C
515 lines
12 KiB
C
/* Canny edge detector
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*/
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/*
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This file is part of VIPS.
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VIPS is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA
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*/
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/*
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These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
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*/
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/*
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#define DEBUG
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*/
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif /*HAVE_CONFIG_H*/
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#include <glib/gi18n-lib.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <vips/vips.h>
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typedef struct _VipsCanny {
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VipsOperation parent_instance;
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VipsImage *in;
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VipsImage *out;
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double sigma;
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VipsPrecision precision;
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/* Need an image vector for start_many.
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*/
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VipsImage *args[3];
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} VipsCanny;
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typedef VipsOperationClass VipsCannyClass;
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G_DEFINE_TYPE( VipsCanny, vips_canny, VIPS_TYPE_OPERATION );
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/* Simple 2x2 -1/+1 difference. For uchar, we try to hit the vector path and
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* use an offset rather than -ves. Otherwise it's float or double output.
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*/
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static int
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vips_canny_gradient( VipsImage *in, VipsImage **Gx, VipsImage **Gy )
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{
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VipsImage *scope;
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VipsImage **t;
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VipsPrecision precision;
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scope = vips_image_new();
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t = (VipsImage **) vips_object_local_array( (VipsObject *) scope, 2 );
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t[0] = vips_image_new_matrixv( 2, 2,
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-1.0, 1.0,
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-1.0, 1.0 );
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if( in->BandFmt == VIPS_FORMAT_UCHAR ) {
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precision = VIPS_PRECISION_INTEGER;
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vips_image_set_double( t[0], "offset", 128.0 );
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}
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else
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precision = VIPS_PRECISION_FLOAT;
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if( vips_conv( in, Gx, t[0], "precision", precision, NULL ) ||
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vips_rot90( t[0], &t[1], NULL ) ||
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vips_conv( in, Gy, t[1], "precision", precision, NULL ) ) {
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g_object_unref( scope );
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return( -1 );
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}
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g_object_unref( scope );
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return( 0 );
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}
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/* LUT for calculating atan2() with +/- 4 bits of precision in each axis.
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*/
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static VipsPel vips_canny_polar_atan2[256];
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/* For the uchar path, gx/gy are -128 to +127, and we need -8 to +7 for the
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* atan2 LUT.
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*
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* For G, we should calculate sqrt( gx * gx + gy * gy ), however we are only
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* interested in relative magnitude (max of sqrt), so we can skip the sqrt
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* itself. We need a result that will fit in 0 - 255, so shift down.
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*/
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#define POLAR_UCHAR { \
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for( x = 0; x < r->width; x++ ) { \
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for( band = 0; band < Gx->Bands; band++ ) { \
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int gx = p1[band] - 128; \
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int gy = p2[band] - 128; \
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\
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int i = ((gx >> 4) & 0xf) | (gy & 0xf0); \
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\
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q[0] = (gx * gx + gy * gy + 256) >> 9; \
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q[1] = vips_canny_polar_atan2[i]; \
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\
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q += 2; \
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} \
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\
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p1 += Gx->Bands; \
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p2 += Gx->Bands; \
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} \
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}
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/* Float/double path. We keep the same ranges as the uchar path to reduce
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* confusion.
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*/
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#define POLAR( TYPE ) { \
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TYPE *tp1 = (TYPE *) p1; \
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TYPE *tp2 = (TYPE *) p2; \
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TYPE *tq = (TYPE *) q; \
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\
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for( x = 0; x < r->width; x++ ) { \
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for( band = 0; band < Gx->Bands; band++ ) { \
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double gx = tp1[band]; \
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double gy = tp2[band]; \
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double theta = VIPS_DEG( atan2( gx, gy ) ); \
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\
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tq[0] = (gx * gx + gy * gy + 256.0) / 512.0; \
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tq[1] = 256.0 * fmod( theta + 360.0, 360.0 ) / 360.0; \
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\
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tq += 2; \
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} \
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\
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tp1 += Gx->Bands; \
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tp2 += Gx->Bands; \
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} \
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}
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static int
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vips_canny_polar_generate( VipsRegion *or,
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void *vseq, void *a, void *b, gboolean *stop )
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{
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VipsRegion **in = (VipsRegion **) vseq;
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VipsRect *r = &or->valid;
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VipsImage *Gx = in[0]->im;
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int x, y, band;
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if( vips_reorder_prepare_many( or->im, in, r ) )
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return( -1 );
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for( y = 0; y < r->height; y++ ) {
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VipsPel *p1 = (VipsPel * restrict)
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VIPS_REGION_ADDR( in[0], r->left, r->top + y );
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VipsPel *p2 = (VipsPel * restrict)
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VIPS_REGION_ADDR( in[1], r->left, r->top + y );
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VipsPel *q = (VipsPel * restrict)
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VIPS_REGION_ADDR( or, r->left, r->top + y );
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switch( Gx->BandFmt ) {
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case VIPS_FORMAT_UCHAR:
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POLAR_UCHAR;
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break;
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case VIPS_FORMAT_FLOAT:
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POLAR( float );
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break;
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case VIPS_FORMAT_DOUBLE:
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POLAR( double );
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break;
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default:
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g_assert( FALSE );
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}
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}
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return( 0 );
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}
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static void *
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vips_atan2_init( void *null )
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{
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int i;
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for( i = 0; i < 256; i++ ) {
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/* Use the bottom 4 bits for x, the top 4 for y. The double
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* shift does sign extension, assuming 2s complement.
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*/
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int bits = sizeof( int ) * 8 - 4;
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int x = ((i & 0xf) << bits) >> bits;
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int y = ((i >> 4) & 0x0f) << bits >> bits;
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double theta = VIPS_DEG( atan2( x, y ) ) + 360;
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vips_canny_polar_atan2[i] = 256 * theta / 360;
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}
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return( NULL );
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}
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/* Calculate G/theta from Gx/Gy. We code theta as 0-256 for 0-360
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* and skip the sqrt on G.
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*
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* For a white disc on a black background, theta is 0 at the top, 64 on the
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* left, 128 on the right and 192 on the right edge.
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*/
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static int
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vips_canny_polar( VipsImage **args, VipsImage **out )
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{
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static GOnce once = G_ONCE_INIT;
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g_once( &once, vips_atan2_init, NULL );
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*out = vips_image_new();
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if( vips_image_pipeline_array( *out,
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VIPS_DEMAND_STYLE_THINSTRIP, args ) )
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return( -1 );
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(*out)->Bands *= 2;
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if( vips_image_generate( *out,
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vips_start_many, vips_canny_polar_generate, vips_stop_many,
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args, NULL ) )
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return( -1 );
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return( 0 );
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}
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#define THIN( TYPE ) { \
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TYPE *tp = (TYPE *) p; \
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TYPE *tq = (TYPE *) q; \
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\
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for( x = 0; x < r->width; x++ ) { \
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for( band = 0; band < out_bands; band++ ) { \
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TYPE G = tp[lsk + psk]; \
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TYPE theta = tp[lsk + psk + 1]; \
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int low_theta = ((int) (theta / 32)) & 0x7; \
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int high_theta = (low_theta + 1) & 0x7; \
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TYPE residual = theta - low_theta * 32; \
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TYPE lowa = tp[offset[low_theta]]; \
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TYPE lowb = tp[offset[high_theta]]; \
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TYPE low = (lowa * (32 - residual) + \
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lowb * residual) / 32; \
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TYPE higha = tp[offset[(low_theta + 4) & 0x7]]; \
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TYPE highb = tp[offset[(high_theta + 4) & 0x7]]; \
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TYPE high = (higha * (32 - residual) + \
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highb * residual) / 32; \
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\
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if( G <= low || \
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G < high ) \
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G = 0; \
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\
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tq[band] = G; \
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\
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tp += 2; \
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} \
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\
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tq += out_bands; \
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} \
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}
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static int
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vips_canny_thin_generate( VipsRegion *or,
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void *vseq, void *a, void *b, gboolean *stop )
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{
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VipsRegion *in = (VipsRegion *) vseq;
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VipsRect *r = &or->valid;
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VipsImage *im = in->im;
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int out_bands = or->im->Bands;
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VipsRect rect;
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int x, y, band;
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int lsk;
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int psk;
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int offset[8];
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rect = *r;
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rect.width += 2;
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rect.height += 2;
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if( vips_region_prepare( in, &rect ) )
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return( -1 );
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/* These are in typed units.
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*/
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lsk = VIPS_REGION_LSKIP( in ) / VIPS_IMAGE_SIZEOF_ELEMENT( im );
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psk = VIPS_IMAGE_SIZEOF_PEL( im ) / VIPS_IMAGE_SIZEOF_ELEMENT( im );
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/* For each of the 8 directions, the offset to get to that pixel from
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* the top-left of the 3x3.
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*
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* 1 | 0 | 7
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* --+---+--
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* 2 | X | 6
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* --+---+--
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* 3 | 4 | 5
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*/
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offset[0] = psk;
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offset[1] = 0;
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offset[2] = lsk;
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offset[3] = 2 * lsk;
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offset[4] = 2 * lsk + psk;
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offset[5] = 2 * lsk + 2 * psk;
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offset[6] = lsk + 2 * psk;
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offset[7] = 2 * psk;
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for( y = 0; y < r->height; y++ ) {
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VipsPel *p = (VipsPel * restrict)
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VIPS_REGION_ADDR( in, r->left, r->top + y );
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VipsPel *q = (VipsPel * restrict)
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VIPS_REGION_ADDR( or, r->left, r->top + y );
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switch( im->BandFmt ) {
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case VIPS_FORMAT_UCHAR:
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THIN( unsigned char );
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break;
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case VIPS_FORMAT_FLOAT:
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THIN( float );
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break;
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case VIPS_FORMAT_DOUBLE:
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THIN( double );
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break;
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default:
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g_assert( FALSE );
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}
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}
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return( 0 );
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}
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/* Remove non-maximal edges. At each point, compare the G to the G in either
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* direction and 0 it if it's not the largest.
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*/
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static int
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vips_canny_thin( VipsImage *in, VipsImage **out )
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{
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*out = vips_image_new();
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if( vips_image_pipelinev( *out,
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VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
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return( -1 );
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(*out)->Bands /= 2;
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(*out)->Xsize -= 2;
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(*out)->Ysize -= 2;
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if( vips_image_generate( *out,
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vips_start_one, vips_canny_thin_generate, vips_stop_one,
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in, NULL ) )
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return( -1 );
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return( 0 );
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}
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static int
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vips_canny_build( VipsObject *object )
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{
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VipsCanny *canny = (VipsCanny *) object;
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VipsImage **t = (VipsImage **) vips_object_local_array( object, 6 );
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VipsImage *in;
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if( VIPS_OBJECT_CLASS( vips_canny_parent_class )->build( object ) )
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return( -1 );
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in = canny->in;
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if( vips_gaussblur( in, &t[0], canny->sigma,
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"precision", canny->precision,
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NULL ) )
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return( -1 );
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in = t[0];
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if( vips_canny_gradient( in, &t[1], &t[2] ) )
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return( -1 );
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/* Form (G, theta).
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*/
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canny->args[0] = t[1];
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canny->args[1] = t[2];
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canny->args[2] = NULL;
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if( vips_canny_polar( canny->args, &t[3] ) )
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return( -1 );
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in = t[3];
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/* Expand by two pixels all around, then thin in the direction of the
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* gradient.
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*/
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if( vips_embed( in, &t[4], 1, 1, in->Xsize + 2, in->Ysize + 2,
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"extend", VIPS_EXTEND_COPY,
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NULL ) )
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return( -1 );
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if( vips_canny_thin( t[4], &t[5] ) )
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return( -1 );
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in = t[5];
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g_object_set( object, "out", vips_image_new(), NULL );
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if( vips_image_write( in, canny->out ) )
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return( -1 );
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return( 0 );
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}
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static void
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vips_canny_class_init( VipsCannyClass *class )
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{
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GObjectClass *gobject_class = G_OBJECT_CLASS( class );
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VipsObjectClass *object_class = (VipsObjectClass *) class;
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VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
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gobject_class->set_property = vips_object_set_property;
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gobject_class->get_property = vips_object_get_property;
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object_class->nickname = "canny";
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object_class->description = _( "Canny edge detector" );
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object_class->build = vips_canny_build;
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operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
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VIPS_ARG_IMAGE( class, "in", 1,
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_( "Input" ),
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_( "Input image" ),
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VIPS_ARGUMENT_REQUIRED_INPUT,
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G_STRUCT_OFFSET( VipsCanny, in ) );
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VIPS_ARG_IMAGE( class, "out", 2,
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_( "Output" ),
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_( "Output image" ),
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VIPS_ARGUMENT_REQUIRED_OUTPUT,
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G_STRUCT_OFFSET( VipsCanny, out ) );
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VIPS_ARG_DOUBLE( class, "sigma", 10,
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_( "Sigma" ),
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_( "Sigma of Gaussian" ),
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VIPS_ARGUMENT_OPTIONAL_INPUT,
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G_STRUCT_OFFSET( VipsCanny, sigma ),
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0.01, 1000, 1.4 );
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VIPS_ARG_ENUM( class, "precision", 103,
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_( "Precision" ),
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_( "Convolve with this precision" ),
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VIPS_ARGUMENT_OPTIONAL_INPUT,
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G_STRUCT_OFFSET( VipsCanny, precision ),
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VIPS_TYPE_PRECISION, VIPS_PRECISION_FLOAT );
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}
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static void
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vips_canny_init( VipsCanny *canny )
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{
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canny->sigma = 1.4;
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canny->precision = VIPS_PRECISION_FLOAT;
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}
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/**
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* vips_canny: (method)
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* @in: input image
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* @out: (out): output image
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* @...: %NULL-terminated list of optional named arguments
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*
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* Optional arguments:
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*
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* * @sigma: %gdouble, sigma for gaussian blur
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* * @precision: #VipsPrecision, calculation accuracy
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*
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* Find edges by Canny's method: The maximum of the derivative of the gradient
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* in the direction of the gradient. Output is float, except for uchar input,
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* where output is uchar, and double input, where output is double. Non-complex
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* images only.
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*
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* Use @sigma to control the scale over which gradient is measured. 1.4 is
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* usually a good value.
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*
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* Use @precision to set the precision of edge detection. For uchar images,
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* setting this to #VIPS_PRECISION_INTEGER will make edge detection much
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* faster, but sacrifice some sensitivity.
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*
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* You will probably need to process the output further to eliminate weak
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* edges.
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*
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* See also: vips_sobel().
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*
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* Returns: 0 on success, -1 on error.
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*/
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int
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vips_canny( VipsImage *in, VipsImage **out, ... )
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{
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va_list ap;
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int result;
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va_start( ap, out );
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result = vips_call_split( "canny", ap, in, out );
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va_end( ap );
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return( result );
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}
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