diff --git a/libvips/foreign/joined-openslide2vips.c b/libvips/foreign/joined-openslide2vips.c
new file mode 100644
index 00000000..aa85353b
--- /dev/null
+++ b/libvips/foreign/joined-openslide2vips.c
@@ -0,0 +1,438 @@
+/* Read a virtual microscope slide using OpenSlide.
+ *
+ * Benjamin Gilbert
+ *
+ * Copyright (c) 2011-2012 Carnegie Mellon University
+ *
+ * 26/11/11
+ *	- initial version
+ * 27/11/11
+ *	- fix black background in transparent areas
+ *	- no need to set *stop on fill_region() error return
+ *	- add OpenSlide properties to image metadata
+ *	- consolidate setup into one function
+ *	- support reading arbitrary layers
+ *	- use VIPS_ARRAY()
+ *	- add helper to copy a line of pixels
+ *	- support reading associated images
+ * 7/12/11
+ *	- redirect OpenSlide error logging to vips_error()
+ * 8/12/11
+ *	- add more exposition to documentation
+ * 9/12/11
+ * 	- unpack to a tile cache
+ * 11/12/11
+ * 	- move argb->rgba into conversion
+ * 	- turn into a set of read fns ready to be called from a class
+ * 28/2/12
+ * 	- convert "layer" to "level" where externally visible
+ * 9/4/12
+ * 	- move argb2rgba back in here, we don't have a use for coded pixels
+ * 	- small cleanups
+ * 11/4/12
+ * 	- fail if both level and associated image are specified
+ * 20/9/12
+ *	- update openslide_open error handling for 3.3.0 semantics
+ *	- switch from deprecated _layer_ functions
+ * 11/10/12
+ * 	- look for tile-width and tile-height properties
+ */
+
+/*
+
+    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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+ */
+
+/*
+#define VIPS_DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#ifdef HAVE_OPENSLIDE
+
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <limits.h>
+
+#include <vips/vips.h>
+#include <vips/debug.h>
+
+#include <openslide.h>
+
+#include "openslide2vips.h"
+
+typedef struct {
+	openslide_t *osr;
+
+	char *associated;
+
+	/* Only valid if associated == NULL.
+	 */
+	int32_t level;
+	double downsample;
+	uint32_t bg;
+
+	/* Try to get these from openslide properties.
+	 */
+	int tile_width;
+	int tile_height;
+} ReadSlide;
+
+int
+vips__openslide_isslide( const char *filename )
+{
+	openslide_t *osr;
+	const char *vendor;
+	int ok;
+
+	ok = 0;
+	if( (osr = openslide_open( filename )) ) {
+		/* Generic tiled tiff images can be opened by openslide as
+		 * well. Only offer to load this file if it's not a generic
+		 * tiff since we want vips_tiffload() to handle these.
+		 */
+		vendor = openslide_get_property_value( osr,
+			OPENSLIDE_PROPERTY_NAME_VENDOR );
+
+		/* vendor will be NULL if osr is in error state.
+		 */
+		if( vendor &&
+			strcmp( vendor, "generic-tiff" ) != 0 )
+			ok = 1;
+
+		openslide_close( osr );
+	} 
+
+	VIPS_DEBUG_MSG( "vips__openslide_isslide: %s - %d\n", filename, ok );
+
+	return( ok );
+}
+
+static void
+readslide_destroy_cb( VipsImage *image, ReadSlide *rslide )
+{
+	VIPS_FREEF( openslide_close, rslide->osr );
+	VIPS_FREE( rslide->associated );
+}
+
+static int
+check_associated_image( openslide_t *osr, const char *name )
+{
+	const char * const *associated;
+
+	for( associated = openslide_get_associated_image_names( osr );
+		*associated != NULL; associated++ )
+		if( strcmp( *associated, name ) == 0 )
+			return( 0 );
+
+	vips_error( "openslide2vips", 
+		"%s", _( "invalid associated image name" ) );
+
+	return( -1 );
+}
+
+static ReadSlide *
+readslide_new( const char *filename, VipsImage *out, 
+	int level, const char *associated )
+{
+	ReadSlide *rslide;
+	int64_t w, h;
+	const char *error;
+	const char *background;
+	const char * const *properties;
+
+	if( level && associated ) {
+		vips_error( "openslide2vips",
+			"%s", _( "specify only one of level or associated "
+			"image" ) );
+		return( NULL );
+	}
+
+	rslide = VIPS_NEW( out, ReadSlide );
+	memset( rslide, 0, sizeof( *rslide ) );
+	g_signal_connect( out, "close", G_CALLBACK( readslide_destroy_cb ),
+		rslide );
+
+	rslide->level = level;
+	rslide->associated = g_strdup( associated );
+
+	/* Non-crazy defaults, override below if we can.
+	 */
+	rslide->tile_width = 256;
+	rslide->tile_height = 256;
+
+	rslide->osr = openslide_open( filename );
+	if( rslide->osr == NULL ) {
+		vips_error( "openslide2vips", 
+			"%s", _( "unsupported slide format" ) );
+		return( NULL );
+	}
+
+	error = openslide_get_error( rslide->osr );
+	if( error ) {
+		vips_error( "openslide2vips",
+			_( "opening slide: %s" ), error );
+		return( NULL );
+	}
+
+	if( level < 0 || 
+		level >= openslide_get_level_count( rslide->osr ) ) {
+		vips_error( "openslide2vips",
+			"%s", _( "invalid slide level" ) );
+		return( NULL );
+	}
+
+	if( associated &&
+		check_associated_image( rslide->osr, associated ) )
+		return( NULL );
+
+	if( associated ) {
+		openslide_get_associated_image_dimensions( rslide->osr,
+			associated, &w, &h );
+		vips_image_set_string( out, "slide-associated-image",
+			associated );
+		vips_demand_hint( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL );
+	} 
+	else {
+		char buf[256];
+		const char *value;
+
+		openslide_get_level_dimensions( rslide->osr,
+			level, &w, &h );
+		rslide->downsample = openslide_get_level_downsample(
+			rslide->osr, level );
+		vips_image_set_int( out, "slide-level", level );
+		vips_demand_hint( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL );
+
+		/* Try to get tile width/height. An undocumented, experimental
+		 * feature.
+		 */
+		vips_snprintf( buf, 256, 
+			"openslide.level[%d].tile-width", level );
+		if( (value = openslide_get_property_value( rslide->osr, buf )) )
+			rslide->tile_width = atoi( value );
+		vips_snprintf( buf, 256, 
+			"openslide.level[%d].tile-height", level );
+		if( (value = openslide_get_property_value( rslide->osr, buf )) )
+			rslide->tile_height = atoi( value );
+		if( value )
+			VIPS_DEBUG_MSG( "readslide_new: found tile-size\n" );
+	}
+
+	rslide->bg = 0xffffff;
+	if( (background = openslide_get_property_value( rslide->osr,
+		OPENSLIDE_PROPERTY_NAME_BACKGROUND_COLOR )) )
+		rslide->bg = strtoul( background, NULL, 16 );
+
+	if( w < 0 || h < 0 || rslide->downsample < 0 ) {
+		vips_error( "openslide2vips", _( "getting dimensions: %s" ),
+			openslide_get_error( rslide->osr ) );
+		return( NULL );
+	}
+	if( w > INT_MAX || 
+		h > INT_MAX ) {
+		vips_error( "openslide2vips",
+			"%s", _( "image dimensions overflow int" ) );
+		return( NULL );
+	}
+
+	vips_image_init_fields( out, w, h, 4, VIPS_FORMAT_UCHAR,
+		VIPS_CODING_NONE, VIPS_INTERPRETATION_RGB, 1.0, 1.0 );
+
+	for( properties = openslide_get_property_names( rslide->osr );
+		*properties != NULL; properties++ )
+		vips_image_set_string( out, *properties,
+			openslide_get_property_value( rslide->osr,
+			*properties ) );
+
+	associated = g_strjoinv( ", ", (char **)
+		openslide_get_associated_image_names( rslide->osr ) );
+	vips_image_set_string( out, "slide-associated-images", associated );
+
+	return( rslide );
+}
+
+int
+vips__openslide_read_header( const char *filename, VipsImage *out, 
+	int level, char *associated )
+{
+	ReadSlide *rslide;
+
+	if( !(rslide = readslide_new( filename, out, level, associated )) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static int
+vips__openslide_generate( VipsRegion *out, 
+	void *_seq, void *_rslide, void *unused, gboolean *stop )
+{
+	ReadSlide *rslide = _rslide;
+	uint32_t bg = rslide->bg;
+	VipsRect *r = &out->valid;
+	int n = r->width * r->height;
+	uint32_t *buf = (uint32_t *) VIPS_REGION_ADDR( out, r->left, r->top );
+
+	const char *error;
+	int i;
+
+	VIPS_DEBUG_MSG( "vips__openslide_generate: %dx%d @ %dx%d\n",
+		r->width, r->height, r->left, r->top );
+
+	/*
+	printf( "vips__openslide_generate: %p %dx%d @ %dx%d\n",
+		g_thread_self(), 
+		r->width, r->height, r->left, r->top );
+	 */
+
+	/* We're inside a cache, so requests should always be
+	 * tile_width by tile_height pixels and on a tile boundary.
+	 */
+	g_assert( (r->left % rslide->tile_width) == 0 );
+	g_assert( (r->top % rslide->tile_height) == 0 );
+	g_assert( r->width <= rslide->tile_width );
+
+	/* The memory on the region should be contiguous for our ARGB->RGBA
+	 * loop below.
+	 */
+	g_assert( VIPS_REGION_LSKIP( out ) == r->width * 4 );
+
+	openslide_read_region( rslide->osr, 
+		buf,
+		r->left * rslide->downsample, 
+		r->top * rslide->downsample, 
+		rslide->level,
+		r->width, r->height ); 
+
+	error = openslide_get_error( rslide->osr );
+	if( error ) {
+		vips_error( "openslide2vips", 
+			_( "reading region: %s" ), error );
+
+		return( -1 );
+	}
+
+	/* Convert from ARGB to RGBA and undo premultiplication. Since we are
+	 * inside a cache, we know buf must be continuous.
+	 */
+	for( i = 0; i < n; i++ ) {
+		uint32_t *p = buf + i;
+		uint32_t x = *p;
+		uint8_t a = x >> 24;
+		VipsPel *out = (VipsPel *) p;
+
+		if( a != 0 ) {
+			out[0] = 255 * ((x >> 16) & 255) / a;
+			out[1] = 255 * ((x >> 8) & 255) / a;
+			out[2] = 255 * (x & 255) / a;
+			out[3] = a;
+		} 
+		else {
+			/* Use background color.
+			 */
+			out[0] = (bg >> 16) & 255;
+			out[1] = (bg >> 8) & 255;
+			out[2] = bg & 255;
+			out[3] = 0;
+		}
+	}
+
+	return( 0 );
+}
+
+int
+vips__openslide_read( const char *filename, VipsImage *out, int level )
+{
+	ReadSlide *rslide;
+	VipsImage *raw;
+	VipsImage *t;
+
+	VIPS_DEBUG_MSG( "vips__openslide_read: %s %d\n", 
+		filename, level );
+
+	raw = vips_image_new();
+	vips_object_local( out, raw );
+
+	if( !(rslide = readslide_new( filename, raw, level, NULL )) )
+		return( -1 );
+
+	if( vips_image_generate( raw, 
+		NULL, vips__openslide_generate, NULL, rslide, NULL ) )
+		return( -1 );
+
+	/* Copy to out, adding a cache. Enough tiles for a complete row, plus
+	 * 50%.
+	 */
+	if( vips_tilecache( raw, &t, 
+		"tile_width", rslide->tile_width, 
+		"tile_height", rslide->tile_height,
+		"max_tiles", 
+			(int) (1.5 * (1 + raw->Xsize / rslide->tile_width)),
+		"threaded", TRUE,
+		NULL ) ) 
+		return( -1 );
+	if( vips_image_write( t, out ) ) {
+		g_object_unref( t );
+		return( -1 );
+	}
+	g_object_unref( t );
+
+	return( 0 );
+}
+
+int
+vips__openslide_read_associated( const char *filename, VipsImage *out, 
+	const char *associated )
+{
+	ReadSlide *rslide;
+	VipsImage *raw;
+	const char *error;
+
+	VIPS_DEBUG_MSG( "vips__openslide_read_associated: %s %s\n", 
+		filename, associated );
+
+	/* Memory buffer. Get associated directly to this, then copy to out.
+	 */
+	raw = vips_image_new_buffer();
+	vips_object_local( out, raw );
+
+	if( !(rslide = readslide_new( filename, raw, 0, associated )) ||
+		vips_image_write_prepare( raw ) )
+		return( -1 );
+	openslide_read_associated_image( rslide->osr, rslide->associated, 
+		(uint32_t *) VIPS_IMAGE_ADDR( raw, 0, 0 ) );
+	error = openslide_get_error( rslide->osr );
+	if( error ) {
+		vips_error( "openslide2vips",
+			_( "reading associated image: %s" ), error );
+		return( -1 );
+	}
+
+	if( vips_image_write( raw, out ) ) 
+		return( -1 );
+
+	return( 0 );
+}
+
+#endif /*HAVE_OPENSLIDE*/
diff --git a/libvips/foreign/split-openslide2vips.c b/libvips/foreign/split-openslide2vips.c
new file mode 100644
index 00000000..1997059c
--- /dev/null
+++ b/libvips/foreign/split-openslide2vips.c
@@ -0,0 +1,500 @@
+/* Read a virtual microscope slide using OpenSlide.
+ *
+ * Benjamin Gilbert
+ *
+ * Copyright (c) 2011-2012 Carnegie Mellon University
+ *
+ * 26/11/11
+ *	- initial version
+ * 27/11/11
+ *	- fix black background in transparent areas
+ *	- no need to set *stop on fill_region() error return
+ *	- add OpenSlide properties to image metadata
+ *	- consolidate setup into one function
+ *	- support reading arbitrary layers
+ *	- use VIPS_ARRAY()
+ *	- add helper to copy a line of pixels
+ *	- support reading associated images
+ * 7/12/11
+ *	- redirect OpenSlide error logging to vips_error()
+ * 8/12/11
+ *	- add more exposition to documentation
+ * 9/12/11
+ * 	- unpack to a tile cache
+ * 11/12/11
+ * 	- move argb->rgba into conversion
+ * 	- turn into a set of read fns ready to be called from a class
+ * 28/2/12
+ * 	- convert "layer" to "level" where externally visible
+ * 9/4/12
+ * 	- move argb2rgba back in here, we don't have a use for coded pixels
+ * 	- small cleanups
+ * 11/4/12
+ * 	- fail if both level and associated image are specified
+ * 20/9/12
+ *	- update openslide_open error handling for 3.3.0 semantics
+ *	- switch from deprecated _layer_ functions
+ * 4/10/12
+ * 	- open the image once for each thread, so we get some parallelism on
+ * 	  decode
+ * 11/10/12
+ * 	- look for tile-width and tile-height properties
+ */
+
+/*
+
+    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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+ */
+
+/*
+#define VIPS_DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#ifdef HAVE_OPENSLIDE
+
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <limits.h>
+
+#include <vips/vips.h>
+#include <vips/debug.h>
+
+#include <openslide.h>
+
+#include "openslide2vips.h"
+
+typedef struct {
+	openslide_t *osr;
+	char *filename;
+
+	char *associated;
+
+	/* Only valid if associated == NULL.
+	 */
+	int32_t level;
+	double downsample;
+	uint32_t bg;
+
+	/* Try to get these from openslide properties.
+	 */
+	int tile_width;
+	int tile_height;
+} ReadSlide;
+
+int
+vips__openslide_isslide( const char *filename )
+{
+	openslide_t *osr;
+	const char *vendor;
+	int ok;
+
+	ok = 0;
+	if( (osr = openslide_open( filename )) ) {
+		/* Generic tiled tiff images can be opened by openslide as
+		 * well. Only offer to load this file if it's not a generic
+		 * tiff since we want vips_tiffload() to handle these.
+		 */
+		vendor = openslide_get_property_value( osr,
+			OPENSLIDE_PROPERTY_NAME_VENDOR );
+
+		/* vendor will be NULL if osr is in error state.
+		 */
+		if( vendor &&
+			strcmp( vendor, "generic-tiff" ) != 0 )
+			ok = 1;
+
+		openslide_close( osr );
+	} 
+
+	VIPS_DEBUG_MSG( "vips__openslide_isslide: %s - %d\n", filename, ok );
+
+	return( ok );
+}
+
+static void
+readslide_destroy_cb( VipsImage *image, ReadSlide *rslide )
+{
+	VIPS_FREEF( openslide_close, rslide->osr );
+	VIPS_FREE( rslide->associated );
+}
+
+static int
+check_associated_image( openslide_t *osr, const char *name )
+{
+	const char * const *associated;
+
+	for( associated = openslide_get_associated_image_names( osr );
+		*associated != NULL; associated++ )
+		if( strcmp( *associated, name ) == 0 )
+			return( 0 );
+
+	vips_error( "openslide2vips", 
+		"%s", _( "invalid associated image name" ) );
+
+	return( -1 );
+}
+
+static ReadSlide *
+readslide_new( const char *filename, VipsImage *out, 
+	int level, const char *associated )
+{
+	ReadSlide *rslide;
+	int64_t w, h;
+	const char *error;
+	const char *background;
+	const char * const *properties;
+
+	if( level && associated ) {
+		vips_error( "openslide2vips",
+			"%s", _( "specify only one of level or associated "
+			"image" ) );
+		return( NULL );
+	}
+
+	rslide = VIPS_NEW( out, ReadSlide );
+	memset( rslide, 0, sizeof( *rslide ) );
+	g_signal_connect( out, "close", G_CALLBACK( readslide_destroy_cb ),
+		rslide );
+
+	rslide->filename = g_strdup( filename );
+	rslide->level = level;
+	rslide->associated = g_strdup( associated );
+
+	/* Non-crazy defaults, override below if we can.
+	 */
+	rslide->tile_width = 256;
+	rslide->tile_height = 256;
+
+	rslide->osr = openslide_open( rslide->filename );
+	if( rslide->osr == NULL ) {
+		vips_error( "openslide2vips", 
+			"%s", _( "unsupported slide format" ) );
+		return( NULL );
+	}
+
+	error = openslide_get_error( rslide->osr );
+	if( error ) {
+		vips_error( "openslide2vips",
+			_( "opening slide: %s" ), error );
+		return( NULL );
+	}
+
+	if( level < 0 || 
+		level >= openslide_get_level_count( rslide->osr ) ) {
+		vips_error( "openslide2vips",
+			"%s", _( "invalid slide level" ) );
+		return( NULL );
+	}
+
+	if( associated &&
+		check_associated_image( rslide->osr, associated ) )
+		return( NULL );
+
+	if( associated ) {
+		openslide_get_associated_image_dimensions( rslide->osr,
+			associated, &w, &h );
+		vips_image_set_string( out, "slide-associated-image",
+			associated );
+		vips_demand_hint( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL );
+	} 
+	else {
+		char buf[256];
+		const char *value;
+
+		openslide_get_level_dimensions( rslide->osr,
+			level, &w, &h );
+		rslide->downsample = openslide_get_level_downsample(
+			rslide->osr, level );
+		vips_image_set_int( out, "slide-level", level );
+		vips_demand_hint( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL );
+
+		/* Try to get tile width/height. An undocumented, experimental
+		 * feature.
+		 */
+		vips_snprintf( buf, 256, 
+			"openslide.level[%d].tile-width", level );
+		if( (value = openslide_get_property_value( rslide->osr, buf )) )
+			rslide->tile_width = atoi( value );
+		vips_snprintf( buf, 256, 
+			"openslide.level[%d].tile-height", level );
+		if( (value = openslide_get_property_value( rslide->osr, buf )) )
+			rslide->tile_height = atoi( value );
+		if( value )
+			VIPS_DEBUG_MSG( "readslide_new: found tile-size\n" );
+	}
+
+	rslide->bg = 0xffffff;
+	if( (background = openslide_get_property_value( rslide->osr,
+		OPENSLIDE_PROPERTY_NAME_BACKGROUND_COLOR )) )
+		rslide->bg = strtoul( background, NULL, 16 );
+
+	if( w < 0 || h < 0 || rslide->downsample < 0 ) {
+		vips_error( "openslide2vips", _( "getting dimensions: %s" ),
+			openslide_get_error( rslide->osr ) );
+		return( NULL );
+	}
+	if( w > INT_MAX || 
+		h > INT_MAX ) {
+		vips_error( "openslide2vips",
+			"%s", _( "image dimensions overflow int" ) );
+		return( NULL );
+	}
+
+	vips_image_init_fields( out, w, h, 4, VIPS_FORMAT_UCHAR,
+		VIPS_CODING_NONE, VIPS_INTERPRETATION_RGB, 1.0, 1.0 );
+
+	for( properties = openslide_get_property_names( rslide->osr );
+		*properties != NULL; properties++ )
+		vips_image_set_string( out, *properties,
+			openslide_get_property_value( rslide->osr,
+			*properties ) );
+
+	associated = g_strjoinv( ", ", (char **)
+		openslide_get_associated_image_names( rslide->osr ) );
+	vips_image_set_string( out, "slide-associated-images", associated );
+
+	return( rslide );
+}
+
+int
+vips__openslide_read_header( const char *filename, VipsImage *out, 
+	int level, char *associated )
+{
+	ReadSlide *rslide;
+
+	if( !(rslide = readslide_new( filename, out, level, associated )) )
+		return( -1 );
+
+	return( 0 );
+}
+
+/* One of these for each thread.
+ */
+typedef struct {
+	openslide_t *osr;
+
+	/* A mem buffer we can read to. This must be continuous.
+	 */
+	uint32_t *buf;
+	size_t size;
+
+} Seq;
+
+static void *
+vips__openslide_start( VipsImage *out, void *_rslide, void *unused )
+{
+	ReadSlide *rslide = _rslide;
+	Seq *seq;
+
+	if( !(seq = VIPS_NEW( out, Seq )) )
+		return( NULL );
+	seq->buf = NULL;
+	if( !(seq->osr = openslide_open( rslide->filename )) ) {
+		vips_error( "openslide2vips", 
+			"%s", _( "unsupported slide format" ) );
+		return( NULL );
+	}
+
+	return( (void *) seq );
+}
+
+static int
+vips__openslide_generate( VipsRegion *out, 
+	void *_seq, void *_rslide, void *unused, gboolean *stop )
+{
+	Seq *seq = (Seq *) _seq;
+	ReadSlide *rslide = _rslide;
+	uint32_t bg = rslide->bg;
+	VipsRect *r = &out->valid;
+	uint32_t *p;
+
+	const char *error;
+	int x, y;
+
+	VIPS_DEBUG_MSG( "vips__openslide_generate: %dx%d @ %dx%d\n",
+		r->width, r->height, r->left, r->top );
+
+	/* Make sure our buffer is large enough.
+	 */
+	if( !seq->buf ||
+		(size_t) r->width * r->height > seq->size ) {
+		seq->size = (size_t) r->width * r->height;
+		VIPS_FREE( seq->buf );
+		if( !(seq->buf = (uint32_t *) VIPS_ARRAY( NULL, seq->size,
+			uint32_t )) )
+			return( -1 );
+	}
+
+	/* We're inside a cache, so requests should always be
+	 * tile_width by tile_height pixels and on a tile boundary.
+	 */
+	g_assert( (r->left % rslide->tile_width) == 0 );
+	g_assert( (r->top % rslide->tile_height) == 0 );
+	g_assert( r->width <= rslide->tile_width );
+	g_assert( r->height <= rslide->tile_height );
+
+	openslide_read_region( seq->osr, 
+		seq->buf,
+		r->left * rslide->downsample, 
+		r->top * rslide->downsample, 
+		rslide->level,
+		r->width, r->height ); 
+
+	error = openslide_get_error( seq->osr );
+	if( error ) {
+		vips_error( "openslide2vips", 
+			_( "reading region: %s" ), error );
+
+		return( -1 );
+	}
+
+	/* Convert from ARGB to RGBA and undo premultiplication.
+	 */
+	p = seq->buf;
+	for( y = 0; y < r->height; y++ ) {
+		VipsPel *q = (VipsPel *) 
+			VIPS_REGION_ADDR( out, r->left, r->top + y ); 
+
+		for( x = 0; x < r->width; x++ ) {
+			uint32_t b = p[x];
+			uint8_t a = b >> 24;
+
+			if( a != 0 ) {
+				q[0] = 255 * ((b >> 16) & 255) / a;
+				q[1] = 255 * ((b >> 8) & 255) / a;
+				q[2] = 255 * (b & 255) / a;
+				q[3] = b;
+			} 
+			else {
+				/* Use background color.
+				 */
+				q[0] = (bg >> 16) & 255;
+				q[1] = (bg >> 8) & 255;
+				q[2] = bg & 255;
+				q[3] = 0;
+			}
+
+			q += 4;
+		}
+
+		p += r->width;
+	}
+
+	return( 0 );
+}
+
+static int
+vips__openslide_stop( void *_seq, void *a, void *b )
+{
+	Seq *seq = (Seq *) _seq;
+
+	VIPS_FREEF( openslide_close, seq->osr );
+	VIPS_FREE( seq->buf );
+
+	return( 0 );
+}
+
+int
+vips__openslide_read( const char *filename, VipsImage *out, int level )
+{
+	ReadSlide *rslide;
+
+	VIPS_DEBUG_MSG( "vips__openslide_read: %s %d\n", 
+		filename, level );
+
+	/* Tile cache: keep enough for two complete rows of tiles. OpenSlide
+	 * has its own tile cache, but it's not large enough for a complete
+	 * scan line.
+	 */
+	VipsImage *raw;
+	VipsImage *t;
+
+	raw = vips_image_new();
+	vips_object_local( out, raw );
+
+	if( !(rslide = readslide_new( filename, raw, level, NULL )) )
+		return( -1 );
+
+	if( vips_image_generate( raw, 
+		vips__openslide_start, 
+		vips__openslide_generate, 
+		vips__openslide_stop, 
+			rslide, NULL ) )
+		return( -1 );
+
+	/* Copy to out, adding a cache. Enough tiles for a complete row, plus
+	 * 50%.
+	 */
+	if( vips_tilecache( raw, &t, 
+		"tile_width", rslide->tile_width, 
+		"tile_height", rslide->tile_height,
+		"max_tiles", 
+			(int) (1.5 * (1 + raw->Xsize / rslide->tile_width)),
+		"threaded", TRUE,
+		NULL ) ) 
+		return( -1 );
+	if( vips_image_write( t, out ) ) {
+		g_object_unref( t );
+		return( -1 );
+	}
+	g_object_unref( t );
+
+	return( 0 );
+}
+
+int
+vips__openslide_read_associated( const char *filename, VipsImage *out, 
+	const char *associated )
+{
+	ReadSlide *rslide;
+	VipsImage *raw;
+	const char *error;
+
+	VIPS_DEBUG_MSG( "vips__openslide_read_associated: %s %s\n", 
+		filename, associated );
+
+	/* Memory buffer. Get associated directly to this, then copy to out.
+	 */
+	raw = vips_image_new_buffer();
+	vips_object_local( out, raw );
+
+	if( !(rslide = readslide_new( filename, raw, 0, associated )) ||
+		vips_image_write_prepare( raw ) )
+		return( -1 );
+	openslide_read_associated_image( rslide->osr, rslide->associated, 
+		(uint32_t *) VIPS_IMAGE_ADDR( raw, 0, 0 ) );
+	error = openslide_get_error( rslide->osr );
+	if( error ) {
+		vips_error( "openslide2vips",
+			_( "reading associated image: %s" ), error );
+		return( -1 );
+	}
+
+	if( vips_image_write( raw, out ) ) 
+		return( -1 );
+
+	return( 0 );
+}
+
+#endif /*HAVE_OPENSLIDE*/