diff --git a/ChangeLog b/ChangeLog
index 2ef716f9..a9ac3e35 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,8 @@
 - many more wepsave options [Felix Bünemann]
 - added quant_table option to wepsave [Felix Bünemann]
 - added @n option to pdfload 
+- dzsave won't write empty tiles in google mode, thanks bverem, perog,
+  felixbuenemann
 
 15/4/16 started 8.3.1
 - rename vips wrapper script, it was still vips-8.2, thanks Benjamin
diff --git a/TODO b/TODO
index d8dfc955..6692c7f0 100644
--- a/TODO
+++ b/TODO
@@ -3,10 +3,10 @@
 	$ vips copy k2.jpg x.dz[suffix=.jpg[Q=90]]
 	dzsave: not , or ) after parameter
 
-- add n_pages to pdfload
-
 - add more webp tests to py suite
 
+- try moving some more of the CLI tests to py
+
 - the gif tests in the suite sometimes fail with giflib5 because of an
   uninitialized struct in giflib, see
 
diff --git a/libvips/foreign/dzsave.c b/libvips/foreign/dzsave.c
index c4eee553..3a197c7d 100644
--- a/libvips/foreign/dzsave.c
+++ b/libvips/foreign/dzsave.c
@@ -55,6 +55,8 @@
  * 	- allow zip > 4gb if we have a recent libgsf
  * 9/9/15
  * 	- better overlap handling, thanks robclouth 
+ * 24/11/15
+ * 	- don't write almost blank tiles in google mode
  * 25/11/15
  * 	- always strip tile metadata 
  * 16/12/15
@@ -596,6 +598,12 @@ struct _VipsForeignSaveDz {
 	 * Track bytes written here and try to guess when we'll go over.
 	 */
 	size_t bytes_written;
+
+	/* save->background turned into a pixel that matches the image we are
+	 * saving .. used to test for blank tiles.
+	 */
+	VipsPel *ink;
+
 };
 
 typedef VipsForeignSaveClass VipsForeignSaveDzClass;
@@ -1096,6 +1104,53 @@ tile_name( Layer *layer, int x, int y )
 	return( out );
 }
 
+/* Test for tile equal to background colour. In google maps mode, we skip
+ * blank background tiles. 
+ *
+ * Don't use exactly equality, since compression artefacts or noise can upset
+ * this.
+ */
+static gboolean
+tile_equal( VipsImage *image, VipsPel * restrict ink )
+{
+	const int bytes = VIPS_IMAGE_SIZEOF_PEL( image );
+
+	VipsRect rect;
+	VipsRegion *region;
+	int x, y, b;
+
+	region = vips_region_new( image ); 
+
+	/* We know @image is part of a memory buffer, so this will be quick.
+	 */
+	rect.left = 0;
+	rect.top = 0;
+	rect.width = image->Xsize;
+	rect.height = image->Ysize;
+	if( vips_region_prepare( region, &rect ) ) {
+		g_object_unref( region );
+		return( FALSE ); 
+	}
+
+	for( y = 0; y < image->Ysize; y++ ) {
+		VipsPel * restrict p = VIPS_REGION_ADDR( region, 0, y ); 
+
+		for( x = 0; x < image->Xsize; x++ ) {
+			for( b = 0; b < bytes; b++ ) 
+				if( VIPS_ABS( p[b] - ink[b] ) > 5 ) {
+					g_object_unref( region );
+					return( FALSE ); 
+				}
+
+			p += bytes;
+		}
+	}
+
+	g_object_unref( region );
+
+	return( TRUE );
+}
+
 static int
 strip_work( VipsThreadState *state, void *a )
 {
@@ -1116,7 +1171,7 @@ strip_work( VipsThreadState *state, void *a )
 	printf( "strip_work\n" );
 #endif /*DEBUG_VERBOSE*/
 
-	/* If we are centring we may be outside the real pixels. Skip in 
+	/* If we are centering we may be outside the real pixels. Skip in 
 	 * this case, and the viewer will display blank.png for us. 
 	 */
 	if( dz->centre ) {
@@ -1149,6 +1204,22 @@ strip_work( VipsThreadState *state, void *a )
 		state->pos.width, state->pos.height, NULL ) ) 
 		return( -1 );
 
+	/* If we are writing a google map pyramid and the tile is equal to the 
+	 * background, don't save. The viewer will display blank.png for us.
+	 */
+	if( dz->layout == VIPS_FOREIGN_DZ_LAYOUT_GOOGLE &&
+		tile_equal( x, dz->ink ) ) { 
+		g_object_unref( x );
+
+#ifdef DEBUG_VERBOSE
+		printf( "strip_work: skipping blank tile %d x %d\n", 
+			state->x / dz->tile_size, 
+			state->y / dz->tile_size ); 
+#endif /*DEBUG_VERBOSE*/
+
+		return( 0 ); 
+	}
+
 	/* Google tiles need to be padded up to tilesize.
 	 */
 	if( dz->layout == VIPS_FOREIGN_DZ_LAYOUT_GOOGLE ) {
@@ -1596,6 +1667,16 @@ vips_foreign_save_dz_build( VipsObject *object )
 	save->ready = z;
 }
 
+	/* We use ink in google mode to check for blank tiles.
+	 */
+	if( dz->layout == VIPS_FOREIGN_DZ_LAYOUT_GOOGLE ) {
+		if( !(dz->ink = vips__vector_to_ink( 
+			class->nickname, save->ready,
+			VIPS_AREA( save->background )->data, NULL, 
+			VIPS_AREA( save->background )->n )) )
+			return( -1 );
+	}
+
 	/* The real pixels we have from our input. This is about to get
 	 * expanded with background. 
 	 */
diff --git a/libvips/iofuncs/header.c b/libvips/iofuncs/header.c
index 5e913759..61d5b177 100644
--- a/libvips/iofuncs/header.c
+++ b/libvips/iofuncs/header.c
@@ -433,10 +433,10 @@ vips_image_guess_format( const VipsImage *image )
 		break;
 
 	case VIPS_INTERPRETATION_CMYK: 
-		if( image->BandFmt != VIPS_FORMAT_USHORT )
-			format = VIPS_FORMAT_UCHAR;
+		if( image->BandFmt == VIPS_FORMAT_USHORT )
+			format = VIPS_FORMAT_USHORT;
 		else
-			format = image->BandFmt;
+			format = VIPS_FORMAT_UCHAR;
 		break;
 
 	case  VIPS_INTERPRETATION_LABQ:
@@ -453,14 +453,15 @@ vips_image_guess_format( const VipsImage *image )
 		break;
 
 	case  VIPS_INTERPRETATION_MATRIX:
-		if( image->BandFmt != VIPS_FORMAT_DOUBLE )
-			format = VIPS_FORMAT_FLOAT;
+		if( image->BandFmt == VIPS_FORMAT_DOUBLE )
+			format = VIPS_FORMAT_DOUBLE;
 		else
-			format = image->BandFmt;
+			format = VIPS_FORMAT_FLOAT;
 		break;
 
 	default:
-		g_assert_not_reached();
+		format = VIPS_FORMAT_NOTSET;
+		break; 
 	}
 
 	return( format );