diff --git a/ChangeLog b/ChangeLog
index 1171436b..17ef851f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,7 +3,8 @@
   im_LCh2UCS(), im_XYZ2Yxy(), im_Yxy2XYZ(), im_float2rad(), im_rad2float(),
   im_Lab2LabQ(), im_LabQ2Lab(), im_Lab2LabS(), im_LabS2Lab(), im_LabQ2LabS(),
   im_LabS2LabQ(), im_LabQ2disp(), im_XYZ2disp(), im_disp2XYZ(),
-  im_icc_import*(), im_icc_export*(), im_icc_transform*()  as classes
+  im_icc_import*(), im_icc_export*(), im_icc_transform*(), im_dE_fromLab()
+  as classes
 - added vips_colour_convert(), replaces all derived conversions
 - dzsave can write zoomify and google maps layout as well
 - tilecache supports threaded access
diff --git a/libvips/colour/Makefile.am b/libvips/colour/Makefile.am
index bdeac870..08f916b9 100644
--- a/libvips/colour/Makefile.am
+++ b/libvips/colour/Makefile.am
@@ -4,6 +4,7 @@ libcolour_la_SOURCES = \
 	colour.c \
 	colour_funcs.c \
 	colour_dispatch.c \
+	dE76.c \
 	icc_transform.c \
 	Lab2XYZ.c \
 	Lab2LCh.c \
@@ -26,7 +27,6 @@ libcolour_la_SOURCES = \
 	sRGB2XYZ.c \
 	im_lab_morph.c \
 	im_dE00_fromLab.c \
-	im_dECMC_fromLab.c \
-	im_dE_fromLab.c
+	im_dECMC_fromLab.c 
 
 INCLUDES = -I${top_srcdir}/libvips/include @VIPS_CFLAGS@ @VIPS_INCLUDES@ 
diff --git a/libvips/colour/colour.c b/libvips/colour/colour.c
index 6dd84291..d7b148a8 100644
--- a/libvips/colour/colour.c
+++ b/libvips/colour/colour.c
@@ -396,6 +396,179 @@ vips_colour_code_init( VipsColourCode *code )
 {
 }
 
+G_DEFINE_ABSTRACT_TYPE( VipsColourDifference, vips_colour_difference, 
+	VIPS_TYPE_COLOUR );
+
+static int
+vips_colour_difference_build( VipsObject *object )
+{
+	VipsColour *colour = VIPS_COLOUR( object );
+	VipsColourDifference *difference = VIPS_COLOUR_DIFFERENCE( object );
+	VipsColourDifferenceClass *class = 
+		VIPS_COLOUR_DIFFERENCE_GET_CLASS( object ); 
+
+	VipsImage **t;
+	VipsImage *left;
+	VipsImage *right;
+	VipsImage *extra;
+
+	t = (VipsImage **) vips_object_local_array( object, 10 );
+
+	left = difference->left;
+	right = difference->right;
+	extra = NULL;
+
+	/* Unpack LABQ images, 
+	 */
+	if( left && 
+		left->Coding == VIPS_CODING_LABQ ) { 
+		if( vips_LabQ2Lab( left, &t[0], NULL ) )
+			return( -1 );
+		left = t[0];
+	}
+	if( right && 
+		right->Coding == VIPS_CODING_LABQ ) { 
+		if( vips_LabQ2Lab( right, &t[1], NULL ) )
+			return( -1 );
+		right = t[1];
+	}
+
+	if( left && 
+		vips_check_uncoded( VIPS_OBJECT_CLASS( class )->nickname,
+			left ) )
+		return( -1 );
+	if( right && 
+		vips_check_uncoded( VIPS_OBJECT_CLASS( class )->nickname,
+			right ) )
+		return( -1 );
+
+	/* Detach and reattach extra bands, if any. If both left and right
+	 * have extra bands, give up.
+	 */
+	if( left &&
+		left->Bands > 3 &&
+		right &&
+		right->Bands > 3 ) {
+		vips_error( VIPS_OBJECT_CLASS( class )->nickname,
+			"%s", "both images have extra bands" );
+		return( -1 );
+	}
+
+	if( left &&
+		left->Bands > 3 ) {
+		if( vips_extract_band( left, &t[2], 0, 
+			"n", 3, 
+			NULL ) )
+			return( -1 );
+		if( vips_extract_band( left, &t[3], 3, 
+			"n", left->Bands - 3, 
+			NULL ) )
+			return( -1 );
+		left = t[2];
+		extra = t[3];
+	}
+
+	if( right &&
+		right->Bands > 3 ) {
+		if( vips_extract_band( right, &t[4], 0, 
+			"n", 3, 
+			NULL ) )
+			return( -1 );
+		if( vips_extract_band( right, &t[5], 3, 
+			"n", right->Bands - 3, 
+			NULL ) )
+			return( -1 );
+		right = t[4];
+		extra = t[5];
+	}
+
+	if( vips_check_bands_atleast( VIPS_OBJECT_CLASS( class )->nickname,
+		left, 3 ) )
+		return( -1 );
+	if( vips_check_bands_atleast( VIPS_OBJECT_CLASS( class )->nickname,
+		right, 3 ) )
+		return( -1 );
+
+	if( vips_colour_convert( left, &t[6], 
+		difference->interpretation, NULL ) )
+		return( -1 );
+	left = t[6];
+	if( vips_colour_convert( right, &t[7], 
+		difference->interpretation, NULL ) )
+		return( -1 );
+	right = t[7];
+
+	/* We only process float.
+	 */
+	if( vips_cast_float( left, &t[8], NULL ) )
+		return( -1 );
+	left = t[8];
+	if( vips_cast_float( right, &t[9], NULL ) )
+		return( -1 );
+	right = t[9];
+
+	colour->n = 2;
+	colour->in = (VipsImage **) vips_object_local_array( object, 2 );
+	colour->in[0] = left;
+	colour->in[1] = right;
+	if( colour->in[0] )
+		g_object_ref( colour->in[0] );
+	if( colour->in[1] )
+		g_object_ref( colour->in[1] );
+
+	if( VIPS_OBJECT_CLASS( vips_colour_space_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	/* Reattach higher bands, if necessary.
+	 */
+	if( extra ) {
+		VipsImage *x;
+
+		if( vips_bandjoin2( colour->out, extra, &x, NULL ) )
+			return( -1 );
+
+		VIPS_UNREF( colour->out );
+
+		colour->out = x;
+	}
+
+	return( 0 );
+}
+
+static void
+vips_colour_difference_class_init( VipsColourDifferenceClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	vobject_class->nickname = "difference";
+	vobject_class->description = _( "calculate colour difference" );
+	vobject_class->build = vips_colour_difference_build;
+
+	VIPS_ARG_IMAGE( class, "left", 1, 
+		_( "Left" ), 
+		_( "Left-hand input image" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		G_STRUCT_OFFSET( VipsColourDifference, left ) );
+
+	VIPS_ARG_IMAGE( class, "right", 2, 
+		_( "Right" ), 
+		_( "Right-hand input image" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		G_STRUCT_OFFSET( VipsColourDifference, right ) );
+
+}
+
+static void
+vips_colour_difference_init( VipsColourDifference *difference )
+{
+}
+
+
 /* A colour-transforming function.
  */
 typedef int (*VipsColourTransformFn)( VipsImage *in, VipsImage **out, ... );
diff --git a/libvips/colour/colour.h b/libvips/colour/colour.h
index 4e30d448..2e977b53 100644
--- a/libvips/colour/colour.h
+++ b/libvips/colour/colour.h
@@ -163,6 +163,43 @@ typedef struct _VipsColourCodeClass {
 
 GType vips_colour_code_get_type( void );
 
+/* Difference between two colour images. 
+ */
+
+#define VIPS_TYPE_COLOUR_DIFFERENCE (vips_colour_difference_get_type())
+#define VIPS_COLOUR_DIFFERENCE( obj ) \
+	(G_TYPE_CHECK_INSTANCE_CAST( (obj), \
+		VIPS_TYPE_COLOUR_DIFFERENCE, VipsColourDifference ))
+#define VIPS_COLOUR_DIFFERENCE_CLASS( klass ) \
+	(G_TYPE_CHECK_CLASS_CAST( (klass), \
+		VIPS_TYPE_COLOUR_DIFFERENCE, VipsColourDifferenceClass))
+#define VIPS_IS_COLOUR_DIFFERENCE( obj ) \
+	(G_TYPE_CHECK_INSTANCE_TYPE( (obj), VIPS_TYPE_COLOUR_DIFFERENCE ))
+#define VIPS_IS_COLOUR_DIFFERENCE_CLASS( klass ) \
+	(G_TYPE_CHECK_CLASS_TYPE( (klass), VIPS_TYPE_COLOUR_DIFFERENCE ))
+#define VIPS_COLOUR_DIFFERENCE_GET_CLASS( obj ) \
+	(G_TYPE_INSTANCE_GET_CLASS( (obj), \
+		VIPS_TYPE_COLOUR_DIFFERENCE, VipsColourDifferenceClass ))
+
+typedef struct _VipsColourDifference {
+	VipsColour parent_instance;
+
+	VipsImage *left;
+	VipsImage *right;
+
+	/* Both get converted to this space.
+	 */
+	VipsInterpretation interpretation;
+
+} VipsColourDifference;
+
+typedef struct _VipsColourDifferenceClass {
+	VipsColourClass parent_class;
+
+} VipsColourDifferenceClass;
+
+GType vips_colour_difference_get_type( void );
+
 #ifdef __cplusplus
 }
 #endif /*__cplusplus*/
diff --git a/libvips/colour/colour_funcs.c b/libvips/colour/colour_funcs.c
index 094d04e6..e8e64407 100644
--- a/libvips/colour/colour_funcs.c
+++ b/libvips/colour/colour_funcs.c
@@ -68,7 +68,7 @@
 #include <vips/internal.h>
 
 /**
- * im_col_pythagoras:
+ * vips_pythagoras:
  * @L1: Input coordinate 1
  * @a1: Input coordinate 1
  * @b1: Input coordinate 1
@@ -79,13 +79,13 @@
  * Pythagorean distance between two points in colour space. Lab/XYZ/UCS etc.
  */
 float
-im_col_pythagoras( float L1, float a1, float b1, float L2, float a2, float b2 )
+vips_pythagoras( float L1, float a1, float b1, float L2, float a2, float b2 )
 {
 	float dL = L1 - L2;
 	float da = a1 - a2;
 	float db = b1 - b2;
 
-	return( sqrt( dL*dL + da*da + db*db ) );
+	return( sqrt( dL * dL + da * da + db * db ) );
 }
 
 /* Functions to convert from Lab to uniform colour space and back.  
diff --git a/libvips/colour/im_dE_fromLab.c b/libvips/colour/dE76.c
similarity index 52%
rename from libvips/colour/im_dE_fromLab.c
rename to libvips/colour/dE76.c
index 5e208ffc..c8ba51cc 100644
--- a/libvips/colour/im_dE_fromLab.c
+++ b/libvips/colour/dE76.c
@@ -6,6 +6,8 @@
  * 31/10/09
  * 	- use im__colour_binary() 
  * 	- gtkdoc comment
+ * 25/10/12
+ * 	- redone as a class
  */
 
 /*
@@ -40,19 +42,32 @@
 #include <vips/intl.h>
 
 #include <vips/vips.h>
-#include <vips/internal.h>
+#include <vips/debug.h>
+
+#include "colour.h"
+
+typedef struct _VipsdE76 {
+	VipsColourDifference parent_instance;
+
+} VipsdE76;
+
+typedef VipsColourSpaceClass VipsdE76Class;
+
+G_DEFINE_TYPE( VipsdE76, vips_dE76, VIPS_TYPE_COLOUR_DIFFERENCE );
 
 /* Find the difference between two buffers of LAB data.
  */
-void
-imb_dE_fromLab( float **p, float *q, int n )
+static void
+vips_dE76_line( VipsColour *colour, VipsPel *out, VipsPel **in, int width )
 {
-	float *p1 = p[0];
-	float *p2 = p[1];
+	float *p1 = (float *) in[0];
+	float *p2 = (float *) in[1];
+	float *q = (float *) out;
+
 	int x;
 
-	for( x = 0; x < n; x++ ) {
-		q[x] = im_col_pythagoras( 
+	for( x = 0; x < width; x++ ) {
+		q[x] = vips_pythagoras( 
 			p1[0], p1[1], p1[2], p2[0], p2[1], p2[2] );
 
 		p1 += 3;
@@ -60,20 +75,41 @@ imb_dE_fromLab( float **p, float *q, int n )
 	}
 }
 
+static void
+vips_dE76_class_init( VipsdE76Class *class )
+{
+	VipsObjectClass *object_class = (VipsObjectClass *) class;
+	VipsColourClass *colour_class = VIPS_COLOUR_CLASS( class );
+
+	object_class->nickname = "dE76";
+	object_class->description = _( "calculate dE76" );
+
+	colour_class->process_line = vips_dE76_line;
+}
+
+static void
+vips_dE76_init( VipsdE76 *dE76 )
+{
+}
+
 /**
- * im_dE_fromLab:
- * @in1: first input image
- * @in2: second input image
+ * vips_dE76:
+ * @in: input image
  * @out: output image
  *
- * Calculate CIE dE 1976 from two Lab images.
+ * Calculate dE 76.
  *
- * Returns: 0 on success, -1 on error.
+ * Returns: 0 on success, -1 on error
  */
-int 
-im_dE_fromLab( IMAGE *in1, IMAGE *in2, IMAGE *out )
+int
+vips_dE76( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 {
-	return( im__colour_difference( "im_dE_fromLab",
-		in1, in2, out, 
-		(im_wrapmany_fn) imb_dE_fromLab, NULL, NULL ) );
+	va_list ap;
+	int result;
+
+	va_start( ap, out );
+	result = vips_call_split( "dE76", ap, left, right, out );
+	va_end( ap );
+
+	return( result );
 }
diff --git a/libvips/deprecated/vips7compat.c b/libvips/deprecated/vips7compat.c
index f843ff2f..073ccc47 100644
--- a/libvips/deprecated/vips7compat.c
+++ b/libvips/deprecated/vips7compat.c
@@ -2773,3 +2773,20 @@ im_dE_fromXYZ( IMAGE *in1, IMAGE *in2, IMAGE *out )
 
 	return( 0 );
 }
+
+int 
+im_dE_fromLab( IMAGE *in1, IMAGE *in2, IMAGE *out )
+{
+	VipsImage *x;
+
+	if( vips_dE76( in1, in2, &x, 
+		NULL ) )
+		return( -1 );
+	if( im_copy( x, out ) ) {
+		g_object_unref( x );
+		return( -1 );
+	}
+	g_object_unref( x );
+
+	return( 0 );
+}
diff --git a/libvips/include/vips/colour.h b/libvips/include/vips/colour.h
index a31e5fa5..87e744b2 100644
--- a/libvips/include/vips/colour.h
+++ b/libvips/include/vips/colour.h
@@ -168,6 +168,9 @@ int vips_icc_export( VipsImage *in, VipsImage **out, ... )
 int vips_icc_ac2rc( VipsImage *in, VipsImage *out, 
 	const char *profile_filename );
 
+int vips_dE76( VipsImage *left, VipsImage *right, VipsImage **out, ... )
+	__attribute__((sentinel));
+
 void vips_col_Lab2XYZ( float L, float a, float b, 
 	float *X, float *Y, float *Z );
 void vips_col_XYZ2Lab( float X, float Y, float Z, 
@@ -193,7 +196,7 @@ int vips_col_sRGB2XYZ( int r, int g, int b, float *X, float *Y, float *Z );
 
 /* Colour loading and conversion functions.
  */
-float im_col_pythagoras( float L1, float a1, float b1, 
+float vips_pythagoras( float L1, float a1, float b1, 
 	float L2, float a2, float b2 );
 
 float im_col_dECMC( 
@@ -204,7 +207,6 @@ float im_col_dE00(
 int im_dECMC_fromLab( VipsImage *in1, VipsImage *in2, VipsImage *out );
 int im_dE00_fromLab( VipsImage *in1, VipsImage *in2, VipsImage *out );
 int im_dE_fromXYZ( VipsImage *in1, VipsImage *in2, VipsImage *out );
-int im_dE_fromLab( VipsImage *in1, VipsImage *in2, VipsImage *out );
 
 int im_lab_morph( VipsImage *in, VipsImage *out,
 	DOUBLEMASK *mask,
diff --git a/libvips/include/vips/vips7compat.h b/libvips/include/vips/vips7compat.h
index 49567e29..41ecede3 100644
--- a/libvips/include/vips/vips7compat.h
+++ b/libvips/include/vips/vips7compat.h
@@ -89,6 +89,7 @@ extern "C" {
 #define im_col_L2Lucs vips_col_L2Lucs
 #define im_col_C2Cucs vips_col_C2Cucs
 #define im_col_Ch2hucs vips_col_Ch2hucs
+#define im_col_pythagoras vips_pythagoras
 
 #define im_col_make_tables_UCS vips_col_make_tables_UCS
 #define im_col_Lucs2L vips_col_Lucs2L
@@ -775,6 +776,8 @@ int im_UCS2Lab( VipsImage *in, VipsImage *out );
 int im_Lab2UCS( VipsImage *in, VipsImage *out );
 int im_XYZ2UCS( VipsImage *in, VipsImage *out );
 
+int im_dE_fromLab( VipsImage *in1, VipsImage *in2, VipsImage *out );
+
 /* ruby-vips uses this
  */
 #define vips_class_map_concrete_all vips_class_map_all