Merge branch 'master' of github.com:jcupitt/libvips

Conflicts:
	TODO

ChangeLog

@@ -1,4 +1,8 @@
 7/5/15 started 8.1.0
+- add vips_premultiply(), vips_unpremultiply()
+- change the alpha range rules for vips_flatten() to match vips_premultiply()
+- vipsthumbnail uses vips_resize() rather than its own code
+- vipsthumbnail uses vips_premultiply() for better alpha quality
 
 4/5/15 started 8.0.2
 - fix a refcount error in C++ wrapper, thanks huskier

TODO

@@ -1,39 +1,3 @@
-- how odd, why is resize much faster?
-
-	$ time vips resize wtc.tif small.tif 0.25
-	memory: high-water mark 138.09 MB
-	real	0m0.430s
-	user	0m2.700s
-	sys	0m0.172s
-	$ time vipsthumbnail wtc.tif -o small.tif -s 2500
-	memory: high-water mark 210.05 MB
-	real	0m0.959s
-	user	0m9.984s
-	sys	0m0.184s
-
-  about the same speed for jpg
-
-	$ time vips resize big.jpg[shrink=8] small.jpg 0.6666
-	memory: high-water mark 47.21 MB
-	real	0m1.320s
-	user	0m2.216s
-	sys	0m0.060s
-	$ time vipsthumbnail big.jpg -s 2500 -o small.jpg 
-	memory: high-water mark 58.65 MB
-	real	0m1.360s
-	user	0m2.392s
-	sys	0m0.100s
-
-  seems to be because vipsthumbnail is not int shrinking enough:
-
-	 $ vipsthumbnail wtc.tif -o small.tif -s 2500 --vips-info
-	 info: vipsthumbnail: integer shrink by 1
-	 info: vipsthumbnail: residual scale by 0.266752
-
-  should int shrink by 2! vips resize is doing this right, what's the
-  difference?
-
-
 - are the mosaic functions calling vips_fastcor()? it must be very slow
 
   add vips_fastcor_direct()

libvips/conversion/Makefile.am

@@ -7,6 +7,8 @@ libconversion_la_SOURCES = \
 	gamma.c \
 	sequential.c \
 	flatten.c \
+	premultiply.c \
+	unpremultiply.c \
 	cache.c \
 	copy.c \
 	embed.c \

libvips/conversion/conversion.c

@@ -238,6 +238,8 @@ vips_conversion_operation_init( void )
 	extern GType vips_recomb_get_type( void ); 
 	extern GType vips_bandmean_get_type( void ); 
 	extern GType vips_flatten_get_type( void ); 
+	extern GType vips_premultiply_get_type( void ); 
+	extern GType vips_unpremultiply_get_type( void ); 
 	extern GType vips_bandbool_get_type( void ); 
 	extern GType vips_gaussnoise_get_type( void ); 
 	extern GType vips_grid_get_type( void ); 
@@ -277,6 +279,8 @@ vips_conversion_operation_init( void )
 	vips_recomb_get_type(); 
 	vips_bandmean_get_type(); 
 	vips_flatten_get_type(); 
+	vips_premultiply_get_type(); 
+	vips_unpremultiply_get_type(); 
 	vips_bandbool_get_type(); 
 	vips_gaussnoise_get_type(); 
 	vips_grid_get_type(); 

libvips/conversion/flatten.c

@@ -5,6 +5,8 @@
  *
  * 4/1/14
  * 	- better rounding 
+ * 9/5/15
+ * 	- add max_alpha to match vips_premultiply() etc.
  */
 
 /*
@@ -67,6 +69,10 @@ typedef struct _VipsFlatten {
 	 */
 	VipsPel *ink;
 
+	/* Use this to scale alpha to 0 - 1.
+	 */
+	double max_alpha;
+
 } VipsFlatten;
 
 typedef VipsConversionClass VipsFlattenClass;
@@ -75,7 +81,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
 
 /* Flatten with black background.
  */
-#define VIPS_FLATTEN_BLACK( TYPE, MAX ) { \
+#define VIPS_FLATTEN_BLACK( TYPE ) { \
 	TYPE * restrict p = (TYPE *) in; \
 	TYPE * restrict q = (TYPE *) out; \
 	\
@@ -84,7 +90,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
 		int b; \
 		\
 		for( b = 0; b < bands - 1; b++ ) \
-			q[b] = (p[b] * alpha) / (MAX); \
+			q[b] = (p[b] * alpha) / max_alpha; \
 		\
 		p += bands; \
 		q += bands - 1; \
@@ -93,19 +99,19 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
 
 /* Flatten with any background.
  */
-#define VIPS_FLATTEN( TYPE, MAX ) { \
+#define VIPS_FLATTEN( TYPE ) { \
 	TYPE * restrict p = (TYPE *) in; \
 	TYPE * restrict q = (TYPE *) out; \
 	\
 	for( x = 0; x < width; x++ ) { \
 		TYPE alpha = p[bands - 1]; \
-		TYPE nalpha = (MAX) - alpha; \
+		TYPE nalpha = max_alpha - alpha; \
 		TYPE * restrict bg = (TYPE *) flatten->ink; \
 		int b; \
 		\
 		for( b = 0; b < bands - 1; b++ ) \
-			q[b] = (p[b] * alpha) / (MAX) + \
+			q[b] = (p[b] * alpha) / max_alpha + \
-				(bg[b] * nalpha) / (MAX); \
+				(bg[b] * nalpha) / max_alpha; \
 		\
 		p += bands; \
 		q += bands - 1; \
@@ -115,7 +121,7 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
 /* Same, but with float arithmetic. Necessary for int/uint to prevent
  * overflow.
  */
-#define VIPS_FLATTEN_BLACK_FLOAT( TYPE, MAX ) { \
+#define VIPS_FLATTEN_BLACK_FLOAT( TYPE ) { \
 	TYPE * restrict p = (TYPE *) in; \
 	TYPE * restrict q = (TYPE *) out; \
 	\
@@ -124,26 +130,26 @@ G_DEFINE_TYPE( VipsFlatten, vips_flatten, VIPS_TYPE_CONVERSION );
 		int b; \
 		\
 		for( b = 0; b < bands - 1; b++ ) \
-			q[b] = ((double) p[b] * alpha) / (MAX); \
+			q[b] = ((double) p[b] * alpha) / max_alpha; \
 		\
 		p += bands; \
 		q += bands - 1; \
 	} \
 }
 
-#define VIPS_FLATTEN_FLOAT( TYPE, MAX ) { \
+#define VIPS_FLATTEN_FLOAT( TYPE ) { \
 	TYPE * restrict p = (TYPE *) in; \
 	TYPE * restrict q = (TYPE *) out; \
 	\
 	for( x = 0; x < width; x++ ) { \
 		TYPE alpha = p[bands - 1]; \
-		TYPE nalpha = (MAX) - alpha; \
+		TYPE nalpha = max_alpha - alpha; \
 		TYPE * restrict bg = (TYPE *) flatten->ink; \
 		int b; \
 		\
 		for( b = 0; b < bands - 1; b++ ) \
-			q[b] = ((double) p[b] * alpha) / (MAX) + \
+			q[b] = ((double) p[b] * alpha) / max_alpha + \
-				((double) bg[b] * nalpha) / (MAX); \
+				((double) bg[b] * nalpha) / max_alpha; \
 		\
 		p += bands; \
 		q += bands - 1; \
@@ -159,6 +165,7 @@ vips_flatten_black_gen( VipsRegion *or, void *vseq, void *a, void *b,
 	VipsRect *r = &or->valid;
 	int width = r->width;
 	int bands = ir->im->Bands; 
+	double max_alpha = flatten->max_alpha;
 
 	int x, y;
 
@@ -171,37 +178,35 @@ vips_flatten_black_gen( VipsRegion *or, void *vseq, void *a, void *b,
 
 		switch( flatten->in->BandFmt ) { 
 		case VIPS_FORMAT_UCHAR: 
-			VIPS_FLATTEN_BLACK( unsigned char, UCHAR_MAX ); 
+			VIPS_FLATTEN_BLACK( unsigned char ); 
 			break; 
 
 		case VIPS_FORMAT_CHAR: 
-			/* Alpha is 0 - 127? No idea, really.
+			VIPS_FLATTEN_BLACK( signed char ); 
-			 */
-			VIPS_FLATTEN_BLACK( signed char, CHAR_MAX ); 
 			break; 
 
 		case VIPS_FORMAT_USHORT: 
-			VIPS_FLATTEN_BLACK( unsigned short, USHRT_MAX ); 
+			VIPS_FLATTEN_BLACK( unsigned short ); 
 			break; 
 
 		case VIPS_FORMAT_SHORT: 
-			VIPS_FLATTEN_BLACK( signed short, SHRT_MAX ); 
+			VIPS_FLATTEN_BLACK( signed short ); 
 			break; 
 
 		case VIPS_FORMAT_UINT: 
-			VIPS_FLATTEN_BLACK_FLOAT( unsigned int, UINT_MAX ); 
+			VIPS_FLATTEN_BLACK_FLOAT( unsigned int ); 
 			break; 
 
 		case VIPS_FORMAT_INT: 
-			VIPS_FLATTEN_BLACK_FLOAT( signed int, INT_MAX ); 
+			VIPS_FLATTEN_BLACK_FLOAT( signed int ); 
 			break; 
 
 		case VIPS_FORMAT_FLOAT: 
-			VIPS_FLATTEN_BLACK_FLOAT( float, 1.0 ); 
+			VIPS_FLATTEN_BLACK_FLOAT( float ); 
 			break; 
 
 		case VIPS_FORMAT_DOUBLE: 
-			VIPS_FLATTEN_BLACK_FLOAT( double, 1.0 ); 
+			VIPS_FLATTEN_BLACK_FLOAT( double ); 
 			break; 
 
 		case VIPS_FORMAT_COMPLEX: 
@@ -225,6 +230,7 @@ vips_flatten_gen( VipsRegion *or, void *vseq, void *a, void *b,
 	VipsRect *r = &or->valid;
 	int width = r->width;
 	int bands = ir->im->Bands; 
+	double max_alpha = flatten->max_alpha;
 
 	int x, y;
 
@@ -237,37 +243,35 @@ vips_flatten_gen( VipsRegion *or, void *vseq, void *a, void *b,
 
 		switch( flatten->in->BandFmt ) { 
 		case VIPS_FORMAT_UCHAR: 
-			VIPS_FLATTEN( unsigned char, UCHAR_MAX ); 
+			VIPS_FLATTEN( unsigned char ); 
 			break; 
 
 		case VIPS_FORMAT_CHAR: 
-			/* Alpha is 0 - 127? No idea, really.
+			VIPS_FLATTEN( signed char ); 
-			 */
-			VIPS_FLATTEN( signed char, CHAR_MAX ); 
 			break; 
 
 		case VIPS_FORMAT_USHORT: 
-			VIPS_FLATTEN( unsigned short, USHRT_MAX ); 
+			VIPS_FLATTEN( unsigned short ); 
 			break; 
 
 		case VIPS_FORMAT_SHORT: 
-			VIPS_FLATTEN( signed short, SHRT_MAX ); 
+			VIPS_FLATTEN( signed short ); 
 			break; 
 
 		case VIPS_FORMAT_UINT: 
-			VIPS_FLATTEN_FLOAT( unsigned int, UINT_MAX ); 
+			VIPS_FLATTEN_FLOAT( unsigned int ); 
 			break; 
 
 		case VIPS_FORMAT_INT: 
-			VIPS_FLATTEN_FLOAT( signed int, INT_MAX ); 
+			VIPS_FLATTEN_FLOAT( signed int ); 
 			break; 
 
 		case VIPS_FORMAT_FLOAT: 
-			VIPS_FLATTEN_FLOAT( float, 1.0 ); 
+			VIPS_FLATTEN_FLOAT( float ); 
 			break; 
 
 		case VIPS_FORMAT_DOUBLE: 
-			VIPS_FLATTEN_FLOAT( double, 1.0 ); 
+			VIPS_FLATTEN_FLOAT( double ); 
 			break; 
 
 		case VIPS_FORMAT_COMPLEX: 
@@ -304,7 +308,7 @@ vips_flatten_build( VipsObject *object )
 
 	/* Trivial case: fall back to copy().
 	 */
-	if( flatten->in->Bands == 1 ) 
+	if( in->Bands == 1 ) 
 		return( vips_image_write( in, conversion->out ) );
 
 	if( vips_check_noncomplex( class->nickname, in ) )
@@ -380,12 +384,21 @@ vips_flatten_class_init( VipsFlattenClass *class )
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsFlatten, background ),
 		VIPS_TYPE_ARRAY_DOUBLE );
+
+	VIPS_ARG_DOUBLE( class, "max_alpha", 115, 
+		_( "Maximum alpha" ), 
+		_( "Maximum value of alpha channel" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsFlatten, max_alpha ),
+		0, 100000000, 255 );
+
 }
 
 static void
 vips_flatten_init( VipsFlatten *flatten )
 {
 	flatten->background = vips_array_double_newv( 1, 0.0 );
+	flatten->max_alpha= 255.0;
 }
 
 /**
@@ -397,19 +410,24 @@ vips_flatten_init( VipsFlatten *flatten )
  * Optional arguments:
  *
  * @background: #VipsArrayDouble colour for new pixels 
+ * @max_alpha: %gdouble, maximum value for alpha
  *
  * Take the last band of @in as an alpha and use it to blend the
  * remaining channels with @background. 
  *
- * The alpha channel is 0 - MAX for
+ * The alpha channel is 0 - @max_alpha,
- * integer images and 0 - 1 for float images, where MAX means 100% image and 0
+ * where 1 means 100% image and 0
- * means 100% background.  Non-complex images only.
+ * means 100% background.  
- * @background defaults to zero (black). MAX is the largest possible positive
+ * Non-complex images only.
- * value for that int type. 
+ * @background defaults to zero (black). 
+ *
+ * @max_alpha has the default value 255. You will need to set this to 65535
+ * for images with a 16-bit alpha, or perhaps 1.0 for images with a float
+ * alpha. 
  *
  * Useful for flattening PNG images to RGB.
  *
- * See also: pngload().
+ * See also: vips_premultiply(), vips_pngload().
  *
  * Returns: 0 on success, -1 on error
  */

libvips/conversion/premultiply.c

@@ -0,0 +1,316 @@
+/* premultiply alpha
+ *
+ * Author: John Cupitt
+ * Written on: 7/5/15
+ *
+ */
+
+/*
+
+    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., 51 Franklin Street, Fifth Floor, Boston, MA
+    02110-1301  USA
+
+ */
+
+/*
+
+    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
+
+ */
+
+/*
+#define VIPS_DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include <vips/vips.h>
+#include <vips/internal.h>
+#include <vips/debug.h>
+
+#include "pconversion.h"
+
+typedef struct _VipsPremultiply {
+	VipsConversion parent_instance;
+
+	VipsImage *in;
+
+	double max_alpha;
+
+} VipsPremultiply;
+
+typedef VipsConversionClass VipsPremultiplyClass;
+
+G_DEFINE_TYPE( VipsPremultiply, vips_premultiply, VIPS_TYPE_CONVERSION );
+
+/* Premultiply an n-band image.
+ */
+#define PRE_MANY( IN, OUT ) { \
+	IN * restrict p = (IN *) in; \
+	OUT * restrict q = (OUT *) out; \
+	\
+	for( x = 0; x < width; x++ ) { \
+		IN alpha = p[bands - 1]; \
+		IN clip_alpha = VIPS_CLIP( 0, alpha, max_alpha ); \
+		double nalpha = (double) clip_alpha / max_alpha; \
+		\
+		for( i = 0; i < bands - 1; i++ ) \
+			q[i] = p[i] * nalpha; \
+		q[i] = alpha; \
+		\
+		p += bands; \
+		q += bands; \
+	} \
+}
+
+/* Special case for RGBA, it's very common.
+ */
+#define PRE_RGB( IN, OUT ) { \
+	IN * restrict p = (IN *) in; \
+	OUT * restrict q = (OUT *) out; \
+	\
+	for( x = 0; x < width; x++ ) { \
+		IN alpha = p[3]; \
+		IN clip_alpha = VIPS_CLIP( 0, alpha, max_alpha ); \
+		double nalpha = (double) clip_alpha / max_alpha; \
+		\
+		q[0] = p[0] * nalpha; \
+		q[1] = p[1] * nalpha; \
+		q[2] = p[2] * nalpha; \
+		q[3] = alpha; \
+		\
+		p += 4; \
+		q += 4; \
+	} \
+}
+
+#define PRE( IN, OUT ) { \
+	if( bands == 3 ) { \
+		PRE_RGB( IN, OUT ); \
+	} \
+	else { \
+		PRE_MANY( IN, OUT ); \
+	} \
+}
+
+static int
+vips_premultiply_gen( VipsRegion *or, void *vseq, void *a, void *b,
+	gboolean *stop )
+{
+	VipsPremultiply *premultiply = (VipsPremultiply *) b;
+	VipsRegion *ir = (VipsRegion *) vseq;
+	VipsImage *im = ir->im;
+	VipsRect *r = &or->valid;
+	int width = r->width;
+	int bands = im->Bands; 
+	double max_alpha = premultiply->max_alpha;
+
+	int x, y, i;
+
+	if( vips_region_prepare( ir, r ) )
+		return( -1 );
+
+	for( y = 0; y < r->height; y++ ) {
+		VipsPel *in = VIPS_REGION_ADDR( ir, r->left, r->top + y ); 
+		VipsPel *out = VIPS_REGION_ADDR( or, r->left, r->top + y ); 
+
+		switch( im->BandFmt ) { 
+		case VIPS_FORMAT_UCHAR: 
+			PRE( unsigned char, float ); 
+			break; 
+
+		case VIPS_FORMAT_CHAR: 
+			PRE( signed char, float ); 
+			break; 
+
+		case VIPS_FORMAT_USHORT: 
+			PRE( unsigned short, float ); 
+			break; 
+
+		case VIPS_FORMAT_SHORT: 
+			PRE( signed short, float ); 
+			break; 
+
+		case VIPS_FORMAT_UINT: 
+			PRE( unsigned int, float ); 
+			break; 
+
+		case VIPS_FORMAT_INT: 
+			PRE( signed int, float ); 
+			break; 
+
+		case VIPS_FORMAT_FLOAT: 
+			PRE( float, float ); 
+			break; 
+
+		case VIPS_FORMAT_DOUBLE: 
+			PRE( double, double ); 
+			break; 
+
+		case VIPS_FORMAT_COMPLEX: 
+		case VIPS_FORMAT_DPCOMPLEX: 
+		default: 
+			g_assert( 0 ); 
+		} 
+	}
+
+	return( 0 );
+}
+
+
+static int
+vips_premultiply_build( VipsObject *object )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
+	VipsConversion *conversion = VIPS_CONVERSION( object );
+	VipsPremultiply *premultiply = (VipsPremultiply *) object;
+	VipsImage **t = (VipsImage **) vips_object_local_array( object, 1 );
+
+	VipsImage *in;
+
+	if( VIPS_OBJECT_CLASS( vips_premultiply_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	in = premultiply->in; 
+
+	if( vips_image_decode( in, &t[0] ) )
+		return( -1 );
+	in = t[0]; 
+
+	/* Trivial case: fall back to copy().
+	 */
+	if( in->Bands == 1 )
+		return( vips_image_write( in, conversion->out ) );
+
+	if( vips_check_noncomplex( class->nickname, in ) )
+		return( -1 );
+
+	if( vips_image_pipelinev( conversion->out, 
+		VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
+		return( -1 );
+
+	if( in->BandFmt == VIPS_FORMAT_DOUBLE )
+		conversion->out->BandFmt = VIPS_FORMAT_DOUBLE;
+	else
+		conversion->out->BandFmt = VIPS_FORMAT_FLOAT;
+
+	if( vips_image_generate( conversion->out,
+		vips_start_one, vips_premultiply_gen, vips_stop_one, 
+		in, premultiply ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static void
+vips_premultiply_class_init( VipsPremultiplyClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
+	VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
+
+	VIPS_DEBUG_MSG( "vips_premultiply_class_init\n" );
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	vobject_class->nickname = "premultiply";
+	vobject_class->description = _( "premultiply image alpha" );
+	vobject_class->build = vips_premultiply_build;
+
+	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
+
+	VIPS_ARG_IMAGE( class, "in", 1, 
+		_( "Input" ), 
+		_( "Input image" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsPremultiply, in ) );
+
+	VIPS_ARG_DOUBLE( class, "max_alpha", 115, 
+		_( "Maximum alpha" ), 
+		_( "Maximum value of alpha channel" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsPremultiply, max_alpha ),
+		0, 100000000, 255 );
+}
+
+static void
+vips_premultiply_init( VipsPremultiply *premultiply )
+{
+	premultiply->max_alpha = 255.0;
+}
+
+/**
+ * vips_premultiply:
+ * @in: input image
+ * @out: output image
+ * @...: %NULL-terminated list of optional named arguments
+ *
+ * Optional arguments:
+ *
+ * @max_alpha: %gdouble, maximum value for alpha
+ *
+ * Premultiplies any alpha channel. 
+ * The final band is taken to be the alpha
+ * and the bands are transformed as:
+ *
+ * |[
+ *   alpha = clip( 0, in[in.bands - 1], @max_alpha ); 
+ *   norm = alpha / @max_alpha; 
+ *   out = [in[0] * norm, ..., in[in.bands - 1] * norm, alpha];
+ * |]
+ *
+ * So for an N-band image, the first N - 1 bands are multiplied by the clipped 
+ * and normalised final band, the final band is clipped. 
+ * If there is only a single band, 
+ * the image is passed through unaltered.
+ *
+ * The result is
+ * #VIPS_FORMAT_FLOAT unless the input format is #VIPS_FORMAT_DOUBLE, in which
+ * case the output is double as well.
+ *
+ * @max_alpha has the default value 255. You will need to set this to 65535
+ * for images with a 16-bit alpha, or perhaps 1.0 for images with a float
+ * alpha. 
+ *
+ * Non-complex images only.
+ *
+ * See also: vips_unpremultiply(), vips_flatten().
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int
+vips_premultiply( VipsImage *in, VipsImage **out, ... )
+{
+	va_list ap;
+	int result;
+
+	va_start( ap, out );
+	result = vips_call_split( "premultiply", ap, in, out );
+	va_end( ap );
+
+	return( result );
+}

libvips/conversion/unpremultiply.c

@@ -0,0 +1,331 @@
+/* unpremultiply alpha
+ *
+ * Author: John Cupitt
+ * Written on: 7/5/15
+ *
+ */
+
+/*
+
+    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., 51 Franklin Street, Fifth Floor, Boston, MA
+    02110-1301  USA
+
+ */
+
+/*
+
+    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
+
+ */
+
+/*
+#define VIPS_DEBUG
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include <vips/vips.h>
+#include <vips/internal.h>
+#include <vips/debug.h>
+
+#include "pconversion.h"
+
+typedef struct _VipsUnpremultiply {
+	VipsConversion parent_instance;
+
+	VipsImage *in;
+
+	double max_alpha;
+
+} VipsUnpremultiply;
+
+typedef VipsConversionClass VipsUnpremultiplyClass;
+
+G_DEFINE_TYPE( VipsUnpremultiply, vips_unpremultiply, VIPS_TYPE_CONVERSION );
+
+/* Unpremultiply a greyscale (two band) image.
+ */
+#define UNPRE_MANY( IN, OUT ) { \
+	IN * restrict p = (IN *) in; \
+	OUT * restrict q = (OUT *) out; \
+	\
+	for( x = 0; x < width; x++ ) { \
+		IN alpha = p[bands - 1]; \
+		int clip_alpha = VIPS_CLIP( 0, alpha, max_alpha ); \
+		double nalpha = (double) clip_alpha / max_alpha; \
+		\
+		if( clip_alpha == 0 ) \
+			for( i = 0; i < bands - 1; i++ ) \
+				q[i] = 0; \
+		else \
+			for( i = 0; i < bands - 1; i++ ) \
+				q[i] = p[i] / nalpha; \
+		q[i] = clip_alpha; \
+		\
+		p += bands; \
+		q += bands; \
+	} \
+}
+
+/* Unpremultiply an RGB (four band) image.
+ */
+#define UNPRE_RGBA( IN, OUT ) { \
+	IN * restrict p = (IN *) in; \
+	OUT * restrict q = (OUT *) out; \
+	\
+	for( x = 0; x < width; x++ ) { \
+		IN alpha = p[3]; \
+		int clip_alpha = VIPS_CLIP( 0, alpha, max_alpha ); \
+		double nalpha = (double) clip_alpha / max_alpha; \
+		\
+		if( clip_alpha == 0 ) { \
+			q[0] = 0; \
+			q[1] = 0; \
+			q[2] = 0; \
+		} \
+		else { \
+			q[0] = p[0] / nalpha; \
+			q[1] = p[1] / nalpha; \
+			q[2] = p[2] / nalpha; \
+		} \
+		q[3] = clip_alpha; \
+		\
+		p += 4; \
+		q += 4; \
+	} \
+}
+
+#define UNPRE( IN, OUT ) { \
+	if( bands == 4 ) { \
+		UNPRE_RGBA( IN, OUT ); \
+	} \
+	else { \
+		UNPRE_MANY( IN, OUT ); \
+	} \
+}
+
+static int
+vips_unpremultiply_gen( VipsRegion *or, void *vseq, void *a, void *b,
+	gboolean *stop )
+{
+	VipsUnpremultiply *unpremultiply = (VipsUnpremultiply *) b;
+	VipsRegion *ir = (VipsRegion *) vseq;
+	VipsImage *im = ir->im;
+	VipsRect *r = &or->valid;
+	int width = r->width;
+	int bands = im->Bands; 
+	double max_alpha = unpremultiply->max_alpha;
+
+	int x, y, i;
+
+	if( vips_region_prepare( ir, r ) )
+		return( -1 );
+
+	for( y = 0; y < r->height; y++ ) {
+		VipsPel *in = VIPS_REGION_ADDR( ir, r->left, r->top + y ); 
+		VipsPel *out = VIPS_REGION_ADDR( or, r->left, r->top + y ); 
+
+		switch( im->BandFmt ) { 
+		case VIPS_FORMAT_UCHAR: 
+			UNPRE( unsigned char, float ); 
+			break; 
+
+		case VIPS_FORMAT_CHAR: 
+			UNPRE( signed char, float ); 
+			break; 
+
+		case VIPS_FORMAT_USHORT: 
+			UNPRE( unsigned short, float ); 
+			break; 
+
+		case VIPS_FORMAT_SHORT: 
+			UNPRE( signed short, float ); 
+			break; 
+
+		case VIPS_FORMAT_UINT: 
+			UNPRE( unsigned int, float ); 
+			break; 
+
+		case VIPS_FORMAT_INT: 
+			UNPRE( signed int, float ); 
+			break; 
+
+		case VIPS_FORMAT_FLOAT: 
+			UNPRE( float, float ); 
+			break; 
+
+		case VIPS_FORMAT_DOUBLE: 
+			UNPRE( double, double ); 
+			break; 
+
+		case VIPS_FORMAT_COMPLEX: 
+		case VIPS_FORMAT_DPCOMPLEX: 
+		default: 
+			g_assert( 0 ); 
+		} 
+	}
+
+	return( 0 );
+}
+
+
+static int
+vips_unpremultiply_build( VipsObject *object )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
+	VipsConversion *conversion = VIPS_CONVERSION( object );
+	VipsUnpremultiply *unpremultiply = (VipsUnpremultiply *) object;
+	VipsImage **t = (VipsImage **) vips_object_local_array( object, 1 );
+
+	VipsImage *in;
+
+	if( VIPS_OBJECT_CLASS( vips_unpremultiply_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	in = unpremultiply->in; 
+
+	if( vips_image_decode( in, &t[0] ) )
+		return( -1 );
+	in = t[0]; 
+
+	/* Trivial case: fall back to copy().
+	 */
+	if( in->Bands == 1 )
+		return( vips_image_write( in, conversion->out ) );
+
+	if( vips_check_noncomplex( class->nickname, in ) )
+		return( -1 );
+
+	if( vips_image_pipelinev( conversion->out, 
+		VIPS_DEMAND_STYLE_THINSTRIP, in, NULL ) )
+		return( -1 );
+
+	if( in->BandFmt == VIPS_FORMAT_DOUBLE )
+		conversion->out->BandFmt = VIPS_FORMAT_DOUBLE;
+	else
+		conversion->out->BandFmt = VIPS_FORMAT_FLOAT;
+
+	if( vips_image_generate( conversion->out,
+		vips_start_one, vips_unpremultiply_gen, vips_stop_one, 
+		in, unpremultiply ) )
+		return( -1 );
+
+	return( 0 );
+}
+
+static void
+vips_unpremultiply_class_init( VipsUnpremultiplyClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
+	VipsOperationClass *operation_class = VIPS_OPERATION_CLASS( class );
+
+	VIPS_DEBUG_MSG( "vips_unpremultiply_class_init\n" );
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	vobject_class->nickname = "unpremultiply";
+	vobject_class->description = _( "unpremultiply image alpha" );
+	vobject_class->build = vips_unpremultiply_build;
+
+	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
+
+	VIPS_ARG_IMAGE( class, "in", 1, 
+		_( "Input" ), 
+		_( "Input image" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsUnpremultiply, in ) );
+
+	VIPS_ARG_DOUBLE( class, "max_alpha", 115, 
+		_( "Maximum alpha" ), 
+		_( "Maximum value of alpha channel" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsUnpremultiply, max_alpha ),
+		0, 100000000, 255 );
+
+}
+
+static void
+vips_unpremultiply_init( VipsUnpremultiply *unpremultiply )
+{
+	unpremultiply->max_alpha = 255.0;
+}
+
+/**
+ * vips_unpremultiply:
+ * @in: input image
+ * @out: output image
+ * @...: %NULL-terminated list of optional named arguments
+ *
+ * Optional arguments:
+ *
+ * @max_alpha: %gdouble, maximum value for alpha
+ *
+ * Unpremultiplies any alpha channel. 
+ * The final band is taken to be the alpha
+ * and the bands are transformed as:
+ *
+ * |[
+ *   alpha = (int) clip( 0, in[in.bands - 1], @max_alpha ); 
+ *   norm = (double) alpha / @max_alpha; 
+ *   if( alpha == 0 )
+ *   	out = [0, ..., 0, alpha];
+ *   else
+ *   	out = [in[0] / norm, ..., in[in.bands - 1] / norm, alpha];
+ * |]
+ *
+ * So for an N-band image, the first N - 1 bands are divided by the clipped 
+ * and normalised final band, the final band is clipped. 
+ * If there is only a single band, 
+ * the image is passed through unaltered.
+ *
+ * The result is
+ * #VIPS_FORMAT_FLOAT unless the input format is #VIPS_FORMAT_DOUBLE, in which
+ * case the output is double as well.
+ *
+ * @max_alpha has the default value 255. You will need to set this to 65535
+ * for images with a 16-bit alpha, or perhaps 1.0 for images with a float
+ * alpha. 
+ *
+ * Non-complex images only.
+ *
+ * See also: vips_premultiply(), vips_flatten().
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int
+vips_unpremultiply( VipsImage *in, VipsImage **out, ... )
+{
+	va_list ap;
+	int result;
+
+	va_start( ap, out );
+	result = vips_call_split( "unpremultiply", ap, in, out );
+	va_end( ap );
+
+	return( result );
+}

libvips/foreign/foreign.c

@@ -1202,6 +1202,9 @@ vips_foreign_convert_saveable( VipsForeignSave *save )
 
 			if( vips_flatten( in, &out, 
 				"background", save->background,
+				"max_alpha", 
+					in->BandFmt == VIPS_FORMAT_USHORT ?
+						65535.0 : 255.0, 
 				NULL ) ) {
 				g_object_unref( in );
 				return( -1 );

libvips/include/vips/conversion.h

@@ -184,8 +184,13 @@ int vips_recomb( VipsImage *in, VipsImage **out, VipsImage *m, ... )
 int vips_ifthenelse( VipsImage *cond, VipsImage *in1, VipsImage *in2, 
 	VipsImage **out, ... )
 	__attribute__((sentinel));
+
 int vips_flatten( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));
+int vips_premultiply( VipsImage *in, VipsImage **out, ... )
+	__attribute__((sentinel));
+int vips_unpremultiply( VipsImage *in, VipsImage **out, ... )
+	__attribute__((sentinel));
 
 int vips_falsecolour( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));

test/test_conversion.py

@@ -348,23 +348,12 @@ class TestConversion(unittest.TestCase):
             self.assertAlmostEqualObjects(pixel, [20, 0, 41])
 
     def test_flatten(self):
-        max_value = {Vips.BandFormat.UCHAR: 0xff,
+        for fmt in unsigned_formats + [Vips.BandFormat.SHORT, 
-                     Vips.BandFormat.USHORT: 0xffff,
+                Vips.BandFormat.INT] + float_formats:
-                     Vips.BandFormat.UINT: 0xffffffff, 
+            mx = 255
-                     Vips.BandFormat.CHAR: 0x7f,
-                     Vips.BandFormat.SHORT: 0x7fff, 
-                     Vips.BandFormat.INT: 0x7fffffff,
-                     Vips.BandFormat.FLOAT: 1.0,
-                     Vips.BandFormat.DOUBLE: 1.0,
-                     Vips.BandFormat.COMPLEX: 1.0,
-                     Vips.BandFormat.DPCOMPLEX: 1.0}
-        black = self.mono * 0.0
-
-        for fmt in noncomplex_formats:
-            mx = max_value[fmt]
             alpha = mx / 2.0
             nalpha = mx - alpha
-            test = self.colour.bandjoin(black + alpha).cast(fmt)
+            test = self.colour.bandjoin(alpha).cast(fmt)
             pixel = test(30, 30)
 
             predict = [int(x) * alpha / mx for x in pixel[:-1]]
@@ -389,6 +378,46 @@ class TestConversion(unittest.TestCase):
             for x, y in zip(pixel, predict):
                 self.assertLess(abs(x - y), 2)
 
+    def test_premultiply(self):
+        for fmt in unsigned_formats + [Vips.BandFormat.SHORT, 
+                Vips.BandFormat.INT] + float_formats:
+            mx = 255
+            alpha = mx / 2.0
+            nalpha = mx - alpha
+            test = self.colour.bandjoin(alpha).cast(fmt)
+            pixel = test(30, 30)
+
+            predict = [int(x) * alpha / mx for x in pixel[:-1]] + [alpha]
+
+            im = test.premultiply()
+
+            self.assertEqual(im.bands, test.bands)
+            pixel = im(30, 30)
+            for x, y in zip(pixel, predict):
+                # we use float arithetic for int and uint, so the rounding
+                # differs ... don't require huge accuracy
+                self.assertLess(abs(x - y), 2)
+
+    def test_unpremultiply(self):
+        for fmt in unsigned_formats + [Vips.BandFormat.SHORT, 
+                Vips.BandFormat.INT] + float_formats:
+            mx = 255
+            alpha = mx / 2.0
+            nalpha = mx - alpha
+            test = self.colour.bandjoin(alpha).cast(fmt)
+            pixel = test(30, 30)
+
+            predict = [int(x) / (alpha / mx) for x in pixel[:-1]] + [alpha]
+
+            im = test.unpremultiply()
+
+            self.assertEqual(im.bands, test.bands)
+            pixel = im(30, 30)
+            for x, y in zip(pixel, predict):
+                # we use float arithetic for int and uint, so the rounding
+                # differs ... don't require huge accuracy
+                self.assertLess(abs(x - y), 2)
+
     def test_flip(self):
         for fmt in all_formats:
             test = self.colour.cast(fmt)

tools/vipsthumbnail.c

@@ -65,6 +65,9 @@
  * 	- exit with an error code if one or more conversions failed
  * 20/1/15
  * 	- rename -o as -f, keep -o as a hidden flag
+ * 9/5/15
+ * 	- use vips_resize() instead of our own code
+ * 	- premultiply alpha
  */
 
 #ifdef HAVE_CONFIG_H
@@ -94,7 +97,7 @@ static char *output_format = "tn_%s.jpg";
 static char *interpolator = "bilinear";
 static char *export_profile = NULL;
 static char *import_profile = NULL;
-static char *convolution_mask = "mild";
+static char *convolution_mask = "none";
 static gboolean delete_profile = FALSE;
 static gboolean linear_processing = FALSE;
 static gboolean crop_image = FALSE;
@@ -159,25 +162,16 @@ static GOptionEntry options[] = {
 	{ NULL }
 };
 
-/* Calculate the shrink factors. 
+/* Calculate the shrink factor, taking into account auto-rotate, the fit mode,
- *
+ * and so on.
- * We shrink in two stages: first, a shrink with a block average. This can
- * only accurately shrink by integer factors. We then do a second shrink with
- * a supplied interpolator to get the exact size we want.
- *
- * We aim to do the second shrink by roughly half the interpolator's 
- * window_size.
  */
-static int
+static double
-calculate_shrink( VipsImage *im, double *residual, 
+calculate_shrink( VipsImage *im )
-	VipsInterpolate *interp )
 {
 	VipsAngle angle = vips_autorot_get_angle( im ); 
 	gboolean rotate = angle == VIPS_ANGLE_D90 || angle == VIPS_ANGLE_D270;
 	int width = rotate_image && rotate ? im->Ysize : im->Xsize;
 	int height = rotate_image && rotate ? im->Xsize : im->Ysize;
-	const int window_size =
-		interp ?  vips_interpolate_get_window_size( interp ) : 2;
 
 	VipsDirection direction;
 
@@ -203,42 +197,8 @@ calculate_shrink( VipsImage *im, double *residual,
 			direction = VIPS_DIRECTION_HORIZONTAL;
 	}
 
-	double factor = direction == VIPS_DIRECTION_HORIZONTAL ?
+	return( direction == VIPS_DIRECTION_HORIZONTAL ?
-		horizontal : vertical; 
+		horizontal : vertical );  
-
-	/* If the shrink factor is <= 1.0, we need to zoom rather than shrink.
-	 * Just set the factor to 1 in this case.
-	 */
-	double factor2 = factor < 1.0 ? 1.0 : factor;
-
-	/* Int component of factor2. 
-	 *
-	 * We want to shrink by less for interpolators with larger windows.
-	 */
-	int shrink = VIPS_MAX( 1, 
-		floor( factor2 ) / VIPS_MAX( 1, window_size / 2 ) );
-
-	if( residual &&
-		direction == VIPS_DIRECTION_HORIZONTAL ) {
-		/* Size after int shrink. 
-		 */
-		int iwidth = width / shrink;
-
-		/* Therefore residual scale factor is.
-		 */
-		double hresidual = (width / factor) / iwidth; 
-
-		*residual = hresidual;
-	}
-	else if( residual &&
-		direction == VIPS_DIRECTION_VERTICAL ) {
-		int iheight = height / shrink;
-		double vresidual = (height / factor) / iheight; 
-
-		*residual = vresidual;
-	}
-
-	return( shrink );
 }
 
 /* Find the best jpeg preload shrink.
@@ -246,19 +206,22 @@ calculate_shrink( VipsImage *im, double *residual,
 static int
 thumbnail_find_jpegshrink( VipsImage *im )
 {
-	int shrink = calculate_shrink( im, NULL, NULL );
+	double shrink = calculate_shrink( im ); 
 
 	/* We can't use pre-shrunk images in linear mode. libjpeg shrinks in Y
 	 * (of YCbCR), not linear space.
 	 */
-
 	if( linear_processing )
 		return( 1 ); 
-	else if( shrink >= 8 )
+
+	/* We want to leave a bit of shrinking for our interpolator, we don't
+	 * want to do all the shrinking with libjpeg.
+	 */
+	if( shrink >= 16 )
 		return( 8 );
-	else if( shrink >= 4 )
+	else if( shrink >= 8 )
 		return( 4 );
-	else if( shrink >= 2 )
+	else if( shrink >= 4 )
 		return( 2 );
 	else 
 		return( 1 );
@@ -326,17 +289,16 @@ thumbnail_open( VipsObject *process, const char *filename )
 static VipsInterpolate *
 thumbnail_interpolator( VipsObject *process, VipsImage *in )
 {
-	double residual;
+	double shrink = calculate_shrink( in );
-	VipsInterpolate *interp;
 
-	calculate_shrink( in, &residual, NULL );
+	VipsInterpolate *interp;
 
 	/* For images smaller than the thumbnail, we upscale with nearest
 	 * neighbor. Otherwise we make thumbnails that look fuzzy and awful.
 	 */
 	if( !(interp = VIPS_INTERPOLATE( vips_object_new_from_string( 
 		g_type_class_ref( VIPS_TYPE_INTERPOLATE ), 
-		residual > 1.0 ? "nearest" : interpolator ) )) )
+		shrink <= 1.0 ? "nearest" : interpolator ) )) )
 		return( NULL );
 
 	vips_object_local( process, interp );
@@ -385,12 +347,15 @@ thumbnail_shrink( VipsObject *process, VipsImage *in,
 	 */
 	gboolean have_imported;
 
-	int shrink; 
+	/* TRUE if we've premultiplied and need to unpremultiply.
-	double residual; 
+	 */
-	int tile_width;
+	gboolean have_premultiplied;
-	int tile_height;
+
-	int nlines;
+	/* Sniff the incoming image and try to guess what the alpha max is.
-	double sigma;
+	 */
+	double max_alpha;
+
+	double shrink; 
 
 	/* RAD needs special unpacking.
 	 */
@@ -404,6 +369,12 @@ thumbnail_shrink( VipsObject *process, VipsImage *in,
 		in = t[0];
 	}
 
+	/* Try to guess what the maximum alpha might be.
+	 */
+	max_alpha = 255;
+	if( in->BandFmt == VIPS_FORMAT_USHORT )
+		max_alpha = 65535;
+
 	/* In linear mode, we import right at the start. 
 	 *
 	 * We also have to import the whole image if it's CMYK, since
@@ -448,71 +419,42 @@ thumbnail_shrink( VipsObject *process, VipsImage *in,
 		return( NULL ); 
 	in = t[2];
 
-	shrink = calculate_shrink( in, &residual, interp );
+	/* If there's an alpha, we have to premultiply before shrinking. See
-
+	 * https://github.com/jcupitt/libvips/issues/291
-	vips_info( "vipsthumbnail", "integer shrink by %d", shrink );
+	 */
-
+	have_premultiplied = FALSE;
-	if( vips_shrink( in, &t[3], shrink, shrink, NULL ) ) 
+	if( in->Bands == 2 ||
+		(in->Bands == 4 && in->Type != VIPS_INTERPRETATION_CMYK) ||
+		in->Bands == 5 ) {
+		vips_info( "vipsthumbnail", "premultiplying alpha" ); 
+		if( vips_premultiply( in, &t[3], 
+			"max_alpha", max_alpha,
+			NULL ) ) 
 			return( NULL );
 		in = t[3];
+		have_premultiplied = TRUE;
+	}
 
-	/* We want to make sure we read the image sequentially.
+	shrink = calculate_shrink( in );
-	 * However, the convolution we may be doing later will force us 
-	 * into SMALLTILE or maybe FATSTRIP mode and that will break
-	 * sequentiality.
-	 *
-	 * So ... read into a cache where tiles are scanlines, and make sure
-	 * we keep enough scanlines to be able to serve a line of tiles.
-	 *
-	 * We use a threaded tilecache to avoid a deadlock: suppose thread1,
-	 * evaluating the top block of the output, is delayed, and thread2, 
-	 * evaluating the second block, gets here first (this can happen on 
-	 * a heavily-loaded system). 
-	 *
-	 * With an unthreaded tilecache (as we had before), thread2 will get
-	 * the cache lock and start evaling the second block of the shrink. 
-	 * When it reaches the png reader it will stall until the first block 
-	 * has been used ... but it never will, since thread1 will block on 
-	 * this cache lock. 
-	 */
 
-	vips_get_tile_size( in, 
+	vips_info( "vipsthumbnail", "shrink by %g", shrink );
-		&tile_width, &tile_height, &nlines );
+	vips_info( "vipsthumbnail", "%s interpolation", 
-	if( vips_tilecache( in, &t[4], 
+		VIPS_OBJECT_GET_CLASS( interp )->nickname );
-		"tile_width", in->Xsize,
+
-		"tile_height", 10,
+	if( vips_resize( in, &t[4], 1.0 / shrink, 
-		"max_tiles", 1 + (nlines * 2) / 10,
+		"interpolate", interp,
-		"access", VIPS_ACCESS_SEQUENTIAL,
-		"threaded", TRUE, 
 		NULL ) ) 
 		return( NULL );
 	in = t[4];
 
-	/* If the final affine will be doing a large downsample, we can get 
+	if( have_premultiplied ) {
-	 * nasty aliasing on hard edges. Blur before affine to smooth this out.
+		vips_info( "vipsthumbnail", "unpremultiplying alpha" ); 
-	 *
+		if( vips_unpremultiply( in, &t[5], 
-	 * Don't blur for very small shrinks, blur with radius 1 for x1.5
+			"max_alpha", max_alpha,
-	 * shrinks, blur radius 2 for x2.5 shrinks and above, etc.
-	 */
-	sigma = ((1.0 / residual) - 0.5) / 1.5;
-	if( residual < 1.0 &&
-		sigma > 0.1 ) { 
-		if( vips_gaussblur( in, &t[5], sigma, NULL ) )
-			return( NULL );
-		vips_info( "vipsthumbnail", "anti-alias, sigma %g",
-			sigma );
-		in = t[5];
-	}
-
-	if( vips_affine( in, &t[6], residual, 0, 0, residual, 
-		"interpolate", interp,
 			NULL ) ) 
 			return( NULL );
-	in = t[6];
+		in = t[5];
-
+	}
-	vips_info( "vipsthumbnail", "residual scale by %g", residual );
-	vips_info( "vipsthumbnail", "%s interpolation", 
-		VIPS_OBJECT_GET_CLASS( interp )->nickname );
 
 	/* Colour management.
 	 *
@@ -593,8 +535,7 @@ thumbnail_shrink( VipsObject *process, VipsImage *in,
 	/* If we are upsampling, don't sharpen, since nearest looks dumb
 	 * sharpened.
 	 */
-	if( shrink >= 1 && 
+	if( shrink > 1.0 &&
-		residual <= 1.0 && 
 		sharpen ) { 
 		vips_info( "vipsthumbnail", "sharpening thumbnail" );
 		if( vips_conv( in, &t[8], sharpen, NULL ) )