From aaebb3b346c045b010f4d98881174b00a13f569c Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Wed, 27 May 2020 15:24:27 +0100
Subject: [PATCH] fix thumbnail of mono image

we were using RGB as the shrink space
---
 libvips/foreign/vips2tiff.c  | 9 +++++++--
 libvips/resample/thumbnail.c | 9 +++++++--
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/libvips/foreign/vips2tiff.c b/libvips/foreign/vips2tiff.c
index 9ede77a6..338a976f 100644
--- a/libvips/foreign/vips2tiff.c
+++ b/libvips/foreign/vips2tiff.c
@@ -628,6 +628,11 @@ wtiff_write_header( Wtiff *wtiff, Layer *layer )
 
 	int orientation; 
 
+#ifdef DEBUG
+	printf( "wtiff_write_header: sub %d, width %d, height %d\n",
+		layer->sub, layer->width, layer->height );
+#endif /*DEBUG*/
+
 	/* Output base header fields.
 	 */
 	TIFFSetField( tif, TIFFTAG_IMAGEWIDTH, layer->width );
@@ -1699,10 +1704,10 @@ write_strip( VipsRegion *region, VipsRect *area, void *a )
 	Wtiff *wtiff = (Wtiff *) a;
 	Layer *layer = wtiff->layer; 
 
-#ifdef DEBUG
+#ifdef DEBUG_VERBOSE
 	printf( "write_strip: strip at %d, height %d\n", 
 		area->top, area->height );
-#endif/*DEBUG*/
+#endif/*DEBUG_VERBOSE*/
 
 	for(;;) {
 		VipsRect *to = &layer->strip->valid;
diff --git a/libvips/resample/thumbnail.c b/libvips/resample/thumbnail.c
index b2a8c282..5a9c5296 100644
--- a/libvips/resample/thumbnail.c
+++ b/libvips/resample/thumbnail.c
@@ -524,13 +524,12 @@ vips_thumbnail_build( VipsObject *object )
 {
 	VipsThumbnail *thumbnail = VIPS_THUMBNAIL( object );
 	VipsImage **t = (VipsImage **) vips_object_local_array( object, 15 );
-	VipsInterpretation interpretation = thumbnail->linear ?
-		VIPS_INTERPRETATION_scRGB : VIPS_INTERPRETATION_sRGB; 
 
 	VipsImage *in;
 	int preshrunk_page_height;
 	double hshrink;
 	double vshrink;
+	VipsInterpretation interpretation;
 
 	/* TRUE if we've done the import of an ICC transform and still need to
 	 * export.
@@ -628,6 +627,12 @@ vips_thumbnail_build( VipsObject *object )
 	 */
 	if( in->Type == VIPS_INTERPRETATION_CMYK )
 		have_imported = TRUE;
+	if( thumbnail->linear )
+		interpretation = VIPS_INTERPRETATION_scRGB;
+	else if( in->Bands < 3 )
+		interpretation = VIPS_INTERPRETATION_B_W; 
+	else 
+		interpretation = VIPS_INTERPRETATION_sRGB; 
 	g_info( "converting to processing space %s",
 		vips_enum_nick( VIPS_TYPE_INTERPRETATION, interpretation ) ); 
 	if( vips_colourspace( in, &t[2], interpretation, NULL ) )