From 6bf83d1ddc3ea22c14c76145f56ccbc1d0e361bc Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sat, 18 Mar 2017 10:55:38 +0000
Subject: [PATCH] premultiply before startcrop search

or there might be stuff hidden in the fully transparent areas

see https://github.com/jcupitt/libvips/issues/619
---
 libvips/conversion/smartcrop.c | 23 +++++++++++++++++------
 whatsnew-8.5.md                |  4 ++--
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/libvips/conversion/smartcrop.c b/libvips/conversion/smartcrop.c
index c2be29a8..caddf771 100644
--- a/libvips/conversion/smartcrop.c
+++ b/libvips/conversion/smartcrop.c
@@ -257,6 +257,7 @@ vips_smartcrop_build( VipsObject *object )
 	VipsSmartcrop *smartcrop = (VipsSmartcrop *) object;
 	VipsImage **t = (VipsImage **) vips_object_local_array( object, 2 );
 
+	VipsImage *in;
 	int left;
 	int top;
 
@@ -271,6 +272,18 @@ vips_smartcrop_build( VipsObject *object )
 		return( -1 );
 	}
 
+	in = smartcrop->in;
+
+	/* If there's an alpha, we have to premultiply before searching for
+	 * content. There could be stuff in transparent areas which we don't
+	 * want to consider. 
+	 */
+	if( vips_image_hasalpha( in ) ) { 
+		if( vips_premultiply( in, &t[0], NULL ) ) 
+			return( -1 );
+		in = t[0];
+	}
+
 	switch( smartcrop->interesting ) {
 	case VIPS_INTERESTING_NONE:
 		break;
@@ -281,14 +294,12 @@ vips_smartcrop_build( VipsObject *object )
 		break;
 
 	case VIPS_INTERESTING_ENTROPY:
-		if( vips_smartcrop_entropy( smartcrop, 
-			smartcrop->in, &left, &top ) )
+		if( vips_smartcrop_entropy( smartcrop, in, &left, &top ) )
 			return( -1 );
 		break;
 
 	case VIPS_INTERESTING_ATTENTION:
-		if( vips_smartcrop_attention( smartcrop, 
-			smartcrop->in, &left, &top ) )
+		if( vips_smartcrop_attention( smartcrop, in, &left, &top ) )
 			return( -1 );
 		break;
 
@@ -297,9 +308,9 @@ vips_smartcrop_build( VipsObject *object )
 		break;
 	}
 
-	if( vips_extract_area( smartcrop->in, &t[0], 
+	if( vips_extract_area( smartcrop->in, &t[1], 
 			left, top, smartcrop->width, smartcrop->height, NULL ) ||
-		vips_image_write( t[0], conversion->out ) )
+		vips_image_write( t[1], conversion->out ) )
 		return( -1 ); 
 
 	return( 0 );
diff --git a/whatsnew-8.5.md b/whatsnew-8.5.md
index bd11e6fa..c8fea323 100644
--- a/whatsnew-8.5.md
+++ b/whatsnew-8.5.md
@@ -179,5 +179,5 @@ As usual, there are a range of improvements to file format read and write.
 
 ## Other
 
-Many small bug fixes, improvements to the C++ binding. 
-As usual, the ChanegLog has more detail if you're interested.
+Many small bug fixes, improvements to the C++ binding. As usual, the 
+ChangeLog has more detail, if you're interested.