Expose attention center when doing attention-based cropping. (#3164)

* ADded optional output parameter to smartcrop to track the center of
attention.

* Added unit test.

* Added docs & updated changelog.

* Updated argument labels & types in documentation.

ChangeLog

@@ -1,5 +1,6 @@
 master
 
+- expose location of interest when using attention based cropping [ejoebstl]
 - version bump to 8.14
 - remove autotools
 - remove various obsolete scripts

libvips/conversion/smartcrop.c

@@ -14,6 +14,8 @@
  * 	- add low and high
  * 19/3/20 jcupitt
  * 	- add all
+ * 26/11/22 ejoebstl
+ *  - expose location of interest when using attention based cropping
  */
 
 /*
@@ -71,6 +73,9 @@ typedef struct _VipsSmartcrop {
 	int height;
 	VipsInteresting interesting;
 
+	int attention_x;
+	int attention_y;
+
 } VipsSmartcrop;
 
 typedef VipsConversionClass VipsSmartcropClass;
@@ -195,7 +200,7 @@ pythagoras( VipsSmartcrop *smartcrop, VipsImage *in, VipsImage **out )
 
 static int
 vips_smartcrop_attention( VipsSmartcrop *smartcrop, 
-	VipsImage *in, int *left, int *top )
+	VipsImage *in, int *left, int *top, int *attention_x, int *attention_y)
 {
 	/* From smartcrop.js.
 	 */
@@ -290,15 +295,20 @@ vips_smartcrop_attention( VipsSmartcrop *smartcrop,
 	if( vips_sum( &t[14], &t[18], 3, NULL ) ||
 		vips_gaussblur( t[18], &t[19], sigma, NULL ) ||
 		vips_max( t[19], &max, "x", &x_pos, "y", &y_pos, NULL ) )
-		return( -1 ); 
+		return( -1 );
+
+	/* Transform back into image coordinates.
+	*/
+	*attention_x = x_pos / hscale;
+	*attention_y = y_pos / vscale;
 
 	/* Centre the crop over the max.
 	 */
 	*left = VIPS_CLIP( 0, 
-		x_pos / hscale - smartcrop->width / 2, 
+		*attention_x - smartcrop->width / 2, 
 		in->Xsize - smartcrop->width );
 	*top = VIPS_CLIP( 0, 
-		y_pos / vscale - smartcrop->height / 2, 
+		*attention_y - smartcrop->height / 2, 
 		in->Ysize - smartcrop->height ); 
 
 	return( 0 ); 
@@ -316,6 +326,9 @@ vips_smartcrop_build( VipsObject *object )
 	int left;
 	int top;
 
+	int attention_x = 0;
+	int attention_y = 0;
+
 	if( VIPS_OBJECT_CLASS( vips_smartcrop_parent_class )->
 		build( object ) )
 		return( -1 );
@@ -357,7 +370,7 @@ vips_smartcrop_build( VipsObject *object )
 		break;
 
 	case VIPS_INTERESTING_ATTENTION:
-		if( vips_smartcrop_attention( smartcrop, in, &left, &top ) )
+		if( vips_smartcrop_attention( smartcrop, in, &left, &top, &attention_x, &attention_y ) )
 			return( -1 );
 		break;
 
@@ -383,6 +396,11 @@ vips_smartcrop_build( VipsObject *object )
 		break;
 	}
 
+	g_object_set(smartcrop, 
+		"attention_x", attention_x,
+		"attention_y", attention_y,
+		NULL);
+
 	if( vips_extract_area( smartcrop->in, &t[1], 
 			left, top, 
 			smartcrop->width, smartcrop->height, NULL ) ||
@@ -420,7 +438,7 @@ vips_smartcrop_class_init( VipsSmartcropClass *class )
 		G_STRUCT_OFFSET( VipsSmartcrop, width ),
 		1, VIPS_MAX_COORD, 1 );
 
-	VIPS_ARG_INT( class, "height", 5, 
+	VIPS_ARG_INT( class, "height", 5,
 		_( "Height" ), 
 		_( "Height of extract area" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
@@ -434,6 +452,21 @@ vips_smartcrop_class_init( VipsSmartcropClass *class )
 		G_STRUCT_OFFSET( VipsSmartcrop, interesting ),
 		VIPS_TYPE_INTERESTING, VIPS_INTERESTING_ATTENTION );
 
+	VIPS_ARG_INT( class, "attention_x", 2, 
+		_( "Attention x" ),
+		_( "Horizontal position of attention centre" ),
+		VIPS_ARGUMENT_OPTIONAL_OUTPUT,
+		G_STRUCT_OFFSET( VipsSmartcrop, attention_x ),
+		0, VIPS_MAX_COORD, 0 );
+
+	VIPS_ARG_INT( class, "attention_y", 3, 
+		_( "Attention y" ),
+		_( "Vertical position of attention centre" ),
+		VIPS_ARGUMENT_OPTIONAL_OUTPUT,
+		G_STRUCT_OFFSET( VipsSmartcrop, attention_y ),
+		0, VIPS_MAX_COORD, 0 );
+
+
 }
 
 static void
@@ -451,9 +484,11 @@ vips_smartcrop_init( VipsSmartcrop *smartcrop )
  * @...: %NULL-terminated list of optional named arguments
  *
  * Optional arguments:
- *
+ * 
  * * @interesting: #VipsInteresting to use to find interesting areas (default: #VIPS_INTERESTING_ATTENTION)
- *
+ * * @attention_x: %gint, horizontal position of attention centre when using attention based cropping
+ * * @attention_y: %gint, vertical position of attention centre when using attention based cropping
+ * 
  * Crop an image down to a specified width and height by removing boring parts. 
  *
  * Use @interesting to pick the method vips uses to decide which bits of the

test/test-suite/test_conversion.py

@@ -334,6 +334,19 @@ class TestConversion:
         assert test.width == 100
         assert test.height == 100
 
+    @pytest.mark.skipif(pyvips.type_find("VipsOperation", "smartcrop") == 0,
+                        reason="no smartcrop, skipping test")
+    def test_smartcrop_attention(self):
+        test, opts = self.image.smartcrop(
+            100, 100, 
+            interesting=pyvips.enums.Interesting.ATTENTION,
+            attention_x=True, attention_y=True)
+        assert test.width == 100
+        assert test.height == 100
+        
+        assert opts["attention_x"] == 199
+        assert opts["attention_y"] == 234
+
     def test_falsecolour(self):
         for fmt in all_formats:
             test = self.colour.cast(fmt)