make vips_sobel()

cut out of vips_canny()

ChangeLog

@@ -5,6 +5,7 @@
 - hough_line scales width to 0 - 180, not 0 - 360
 - hough_line is 4x faster
 - hough_circle is 2x faster
+- add vips_sobel() and vips_canny() edge detectors
 
 12/2/18 started 8.6.3
 - use pkg-config to find libjpeg, if we can

configure.ac

@@ -1280,8 +1280,8 @@ if test x"$found_introspection" = xyes -a "$VIPS_LIBDIR/girepository-1.0" != "$I
       ;; # ignore for homebrew
     *)
       AC_MSG_RESULT([dnl
-Vips-8.0.typelib will install to $VIPS_LIBDIR/girepository-1.0, but your
+Vips-8.0.typelib will be installed to $VIPS_LIBDIR/girepository-1.0, but 
-system repository seems to be $INTROSPECTION_TYPELIBDIR. 
+your system repository seems to be $INTROSPECTION_TYPELIBDIR. 
 You may need to add this directory to your typelib path, for example:
 
 	export GI_TYPELIB_PATH="$VIPS_LIBDIR/girepository-1.0"
@@ -1313,7 +1313,7 @@ overrides are installed in the correct location.
         ])
       elif test x"$VIPS_PYEXECDIR/gi/overrides" != x"$syspygipath"; then
         AC_MSG_RESULT([dnl
-The vips Python overrides file will install to 
+The vips Python overrides file will be installed to 
 $VIPS_PYEXECDIR/gi/overrides/Vips.py, but your
 system gi overrides seem to be $syspygipath.
 You may need to copy this file, for example:

libvips/convolution/Makefile.am

@@ -2,6 +2,7 @@ noinst_LTLIBRARIES = libconvolution.la
 
 libconvolution_la_SOURCES = \
 	canny.c \
+	sobel.c \
 	convolution.c \
 	pconvolution.h \
 	correlation.c \

libvips/convolution/canny.c

@@ -35,6 +35,17 @@
 #define DEBUG
  */
 
+/* TODO
+ *	- verify that our interpolating max edge works
+ *	- does it actually help much?
+ *	- can skip the sqrt() 
+ *	- support other image types
+ * 	- swap atan2 for a LUT with perhaps +/- 2 or 4 bits
+ *	- check sobel speed with separated and non-sep masks
+ *	- add autothreshold with otsu's method
+ *	- leave blob analysis to a separate pass
+ */
+
 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif /*HAVE_CONFIG_H*/
@@ -53,6 +64,7 @@ typedef struct _VipsCanny {
 	VipsImage *out;
 
 	double sigma; 
+	gboolean interpolate;
 	double low;
 	double high;
 
@@ -65,50 +77,7 @@ typedef VipsOperationClass VipsCannyClass;
 
 G_DEFINE_TYPE( VipsCanny, vips_canny, VIPS_TYPE_OPERATION );
 
-static int
+/* Simple 2x2 -1/+1 difference. 
-vips_canny_gradient_sobel( VipsImage *in, VipsImage **Gx, VipsImage **Gy )
-{
-	VipsImage *scope;
-	VipsImage **t;
-
-	scope = vips_image_new();
-	t = (VipsImage **) vips_object_local_array( (VipsObject *) scope, 20 );
-
-	/* Separated Sobel gives Gx / Gy. 
-	 */
-	t[1] = vips_image_new_matrixv( 1, 3, 1.0, 2.0, 1.0 );
-	t[2] = vips_image_new_matrixv( 3, 1, 1.0, 0.0, -1.0 );
-	vips_image_set_double( t[2], "offset", 128.0 ); 
-	if( vips_conv( in, &t[3], t[1], 
-		"precision", VIPS_PRECISION_INTEGER,
-		NULL ) ||
-		vips_conv( t[3], Gx, t[2], 
-			"precision", VIPS_PRECISION_INTEGER,
-			NULL ) ) {
-		g_object_unref( scope ); 
-		return( -1 );
-	}
-
-	t[5] = vips_image_new_matrixv( 3, 1, 1.0, 2.0, 1.0 );
-	t[6] = vips_image_new_matrixv( 1, 3, 1.0, 0.0, -1.0 );
-	vips_image_set_double( t[6], "offset", 128.0 ); 
-	if( vips_conv( in, &t[7], t[5], 
-		"precision", VIPS_PRECISION_INTEGER,
-		NULL ) ||
-		vips_conv( t[7], Gy, t[6], 
-			"precision", VIPS_PRECISION_INTEGER,
-			NULL ) ) {
-		g_object_unref( scope ); 
-		return( -1 );
-	}
-
-	g_object_unref( scope ); 
-
-	return( 0 ); 
-}
-
-/* Simple -1/+1 difference. The sobel version above does an edge
- * detect as well.
  */
 static int
 vips_canny_gradient_simple( VipsImage *in, VipsImage **Gx, VipsImage **Gy )
@@ -173,10 +142,14 @@ vips_canny_polar_generate( VipsRegion *or,
 				int y = p2[band] - 128;
 				int a = VIPS_DEG( atan2( x, y ) ) + 360;
 
-				/* Faster than hypot() for int args. Scale down
+				/* We should calculate 
-				 * or we'll clip on very hard edges.
+				 * 	0.5 * sqrt( x * x + y * y )
+				 * ie. length of hypot, scaled down to avoid
+				 * clipping. We are only interested in relative
+				 * magnitude, so we can skip the sqrt and just
+				 * shift down 9 bits.
 				 */
-				q[0] = 0.5 * sqrt( x * x + y * y );
+				q[0] = (x * x + y * y + 256) >> 9;
 				q[1] = 256 * a / 360;
 
 				q += 2;
@@ -428,6 +401,8 @@ vips_canny_thresh_generate( VipsRegion *or,
 	VipsCanny *canny = (VipsCanny *) b;
 	VipsRect *r = &or->valid;
 	int sz = r->width * in->im->Bands;
+	VipsPel low = canny->low;
+	VipsPel high = canny->high;
 
 	int x, y;
 
@@ -444,9 +419,9 @@ vips_canny_thresh_generate( VipsRegion *or,
 			int v;
 
 			v = p[x];
-			if( v <= canny->low )
+			if( v <= low )
 				v = 0;
-			else if( v <= canny->high )
+			else if( v <= high )
 				v = 128;
 			else 
 				v = 255;
@@ -509,10 +484,16 @@ vips_canny_build( VipsObject *object )
 	 */
 	if( vips_embed( in, &t[10], 1, 1, in->Xsize + 2, in->Ysize + 2,
 		"extend", VIPS_EXTEND_COPY,
-		NULL ) ||
+		NULL ) )
-		vips_canny_nonmax( t[10], &t[11] ) )
-		//vips_canny_nonmaxi( t[10], &t[11] ) )
 		return( -1 );
+	if( canny->interpolate ) {
+		if( vips_canny_nonmaxi( t[10], &t[11] ) )
+			return( -1 );
+	}
+	else {
+		if( vips_canny_nonmax( t[10], &t[11] ) )
+			return( -1 );
+	}
 	in = t[11];
 
 	/* Double threshold.
@@ -578,6 +559,13 @@ vips_canny_class_init( VipsCannyClass *class )
 		G_STRUCT_OFFSET( VipsCanny, high ),
 		-INFINITY, INFINITY, 7.0 );
 
+	VIPS_ARG_BOOL( class, "interpolate", 13, 
+		_( "Interpolate" ), 
+		_( "Interpolate gradient angles" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsCanny, interpolate ),
+		FALSE );
+
 }
 
 static void

libvips/convolution/convolution.c

@@ -168,6 +168,7 @@ vips_convolution_operation_init( void )
 	extern int vips_spcor_get_type( void ); 
 	extern int vips_sharpen_get_type( void ); 
 	extern int vips_gaussblur_get_type( void ); 
+	extern int vips_sobel_get_type( void ); 
 	extern int vips_canny_get_type( void ); 
 
 	vips_conv_get_type(); 
@@ -182,4 +183,5 @@ vips_convolution_operation_init( void )
 	vips_sharpen_get_type(); 
 	vips_gaussblur_get_type(); 
 	vips_canny_get_type(); 
+	vips_sobel_get_type(); 
 }

libvips/convolution/sobel.c

@@ -0,0 +1,156 @@
+/* Sobel edge detector
+ * 
+ * 2/2/18
+ * 	- from vips_sobel()
+ */
+
+/*
+
+    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 DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include <vips/vips.h>
+
+/* TODO
+ *	- check sobel speed with separated and non-sep masks
+ *	- add an 8-bit sobel path, with offset 128 and code for abs() + abs()
+ */
+
+typedef struct _VipsSobel {
+	VipsOperation parent_instance;
+
+	VipsImage *in;
+	VipsImage *out;
+
+} VipsSobel;
+
+typedef VipsOperationClass VipsSobelClass;
+
+G_DEFINE_TYPE( VipsSobel, vips_sobel, VIPS_TYPE_OPERATION );
+
+static int
+vips_sobel_build( VipsObject *object )
+{
+	VipsSobel *sobel = (VipsSobel *) object;
+	VipsImage **t = (VipsImage **) vips_object_local_array( object, 20 );
+
+	t[1] = vips_image_new_matrixv( 1, 3, 1.0, 2.0, 1.0 );
+	t[2] = vips_image_new_matrixv( 3, 1, 1.0, 0.0, -1.0 );
+	if( vips_conv( sobel->in, &t[3], t[1], NULL ) ||
+		vips_conv( t[3], &t[4], t[2], NULL ) ) 
+		return( -1 );
+
+	t[5] = vips_image_new_matrixv( 3, 1, 1.0, 2.0, 1.0 );
+	t[6] = vips_image_new_matrixv( 1, 3, 1.0, 0.0, -1.0 );
+	if( vips_conv( sobel->in, &t[7], t[5], NULL ) ||
+		vips_conv( t[7], &t[8], t[6], NULL ) ) 
+		return( -1 );
+
+	if( vips_abs( t[4], &t[9], NULL ) ||
+		vips_abs( t[8], &t[10], NULL ) ||
+		vips_add( t[9], t[10], &t[11], NULL ) ||
+		vips_cast( t[11], &t[12], sobel->in->BandFmt, NULL ) )
+		return( -1 ); 
+
+	g_object_set( object, "out", vips_image_new(), NULL ); 
+
+	if( vips_image_write( t[12], sobel->out ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static void
+vips_sobel_class_init( VipsSobelClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	object_class->nickname = "sobel";
+	object_class->description = _( "Sobel edge detector" );
+	object_class->build = vips_sobel_build;
+
+	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
+
+	VIPS_ARG_IMAGE( class, "in", 1, 
+		_( "Input" ), 
+		_( "Input image" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsSobel, in ) );
+
+	VIPS_ARG_IMAGE( class, "out", 2, 
+		_( "Output" ), 
+		_( "Output image" ),
+		VIPS_ARGUMENT_REQUIRED_OUTPUT, 
+		G_STRUCT_OFFSET( VipsSobel, out ) );
+
+}
+
+static void
+vips_sobel_init( VipsSobel *sobel )
+{
+}
+
+/**
+ * vips_sobel: (method)
+ * @in: input image
+ * @out: (out): output image
+ * @...: %NULL-terminated list of optional named arguments
+ *
+ * Simple Sobel edge detector.
+ *
+ * See also: vips_canny().
+ * 
+ * Returns: 0 on success, -1 on error.
+ */
+int 
+vips_sobel( VipsImage *in, VipsImage **out, ... )
+{
+	va_list ap;
+	int result;
+
+	va_start( ap, out );
+	result = vips_call_split( "sobel", ap, in, out );  
+	va_end( ap );
+
+	return( result );
+}

libvips/create/gaussmat.c

@@ -157,6 +157,11 @@ vips_gaussmat_build( VipsObject *object )
 		}
 	}
 
+	/* Make sure we can't make sum == 0: it'd certainly cause /0 later. 
+	 */
+	if( sum == 0 )
+		sum = 1;
+
 	vips_image_set_double( create->out, "scale", sum ); 
 	vips_image_set_double( create->out, "offset", 0.0 ); 
 

libvips/include/vips/convolution.h

@@ -70,6 +70,8 @@ int vips_spcor( VipsImage *in, VipsImage *ref, VipsImage **out, ... )
 int vips_fastcor( VipsImage *in, VipsImage *ref, VipsImage **out, ... )
 	__attribute__((sentinel));
 
+int vips_sobel( VipsImage *in, VipsImage **out, ... )
+	__attribute__((sentinel));
 int vips_canny( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));