diff --git a/ChangeLog b/ChangeLog
index ee4e70d9..e27c6ffd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -70,6 +70,7 @@
 - added im_insertplaceset()
 - im_insertplace() allows small to be outside big
 - added im__colour_binary(), colour ops now work on any image format
+- added im_col_display_get_table(), so display tables are now shared by name
 
 25/3/09 started 7.18.0
 - revised version numbers
diff --git a/TODO b/TODO
index 5e9713fc..5d224b5c 100644
--- a/TODO
+++ b/TODO
@@ -1,7 +1,3 @@
-- im_disp2XYZ() makes a new set of lookup tables for every call, argh
-
-  maybe use disp->name to get built tables from a hash? I think we can say
-  names need to be unique
 
 - more stuff from util.c? too much to do it all now
 
diff --git a/libvips/colour/disp.c b/libvips/colour/disp.c
index 6a1cf9ea..c648a02d 100644
--- a/libvips/colour/disp.c
+++ b/libvips/colour/disp.c
@@ -40,6 +40,7 @@
 #include <ctype.h>
 #include <math.h>
 
+#include <vips/vips.h>
 #include <vips/vips.h>
 
 #ifdef WITH_DMALLOC
@@ -57,6 +58,10 @@
  * but most programs will be better off with im_icc_transform() and friends.
  */
 
+/* Tables we've generated, indexed by display name.
+ */
+static GHashTable *im__col_display_tables = NULL;
+
 /* Values for IM_TYPE_sRGB.
  */
 static struct im_col_display srgb_profile = {
@@ -341,6 +346,9 @@ im_col_make_tables_RGB( IMAGE *im, struct im_col_display *d )
 	double **temp;
 	int i, j;
 
+	printf( "im_col_make_tables_RGB: generating table for %s\n", 
+		d->d_name );
+
 	if( !(table = IM_NEW( im, struct im_col_tab_disp )) )
 		return( NULL );
 
@@ -370,15 +378,35 @@ im_col_make_tables_RGB( IMAGE *im, struct im_col_display *d )
 	return( table );
 }
 
+struct im_col_tab_disp *
+im_col_display_get_table( struct im_col_display *d )
+{
+	struct im_col_tab_disp *table;
+
+	if( !im__col_display_tables )
+		im__col_display_tables = g_hash_table_new( 
+			g_str_hash, g_str_equal );
+
+	if( !(table = g_hash_table_lookup( im__col_display_tables, 
+		d->d_name )) ) {
+		table = im_col_make_tables_RGB( NULL, d );
+		g_hash_table_insert( im__col_display_tables, d->d_name, table );
+	}
+
+	return( table );
+}
+
 /* Computes the transform: r,g,b => Yr,Yg,Yb. It finds Y values in 
  * lookup tables and calculates X, Y, Z.
  */
 int
-im_col_rgb2XYZ( struct im_col_display *d, struct im_col_tab_disp *table,
+im_col_rgb2XYZ( struct im_col_display *d, 
 	int r, int g, int b, float *X, float *Y, float *Z )
 {
-	float Yr, Yg, Yb;
+	struct im_col_tab_disp *table = im_col_display_get_table( d );
 	float *mat = &table->mat_lum2XYZ[0][0];
+
+	float Yr, Yg, Yb;
 	int i;
 
 	if( r < 0 || r > 255 || g < 0 || g > 255 || b < 0 || b > 255 ) {
@@ -425,12 +453,13 @@ im_col_rgb2XYZ( struct im_col_display *d, struct im_col_tab_disp *table,
  * contain an approximation of the right colour.
  */
 int
-im_col_XYZ2rgb( struct im_col_display *d, struct im_col_tab_disp *table, 
-	float X, float Y, float Z, 
-	int *r_ret, int *g_ret, int *b_ret, 
+im_col_XYZ2rgb( struct im_col_display *d, 
+	float X, float Y, float Z, int *r_ret, int *g_ret, int *b_ret, 
 	int *or_ret )
 {
+	struct im_col_tab_disp *table = im_col_display_get_table( d );
 	float *mat = &table->mat_XYZ2lum[0][0];
+
 	int or = 0;		/* Out of range flag */
 
 	float Yr, Yg, Yb;
diff --git a/libvips/colour/im_Lab2LCh.c b/libvips/colour/im_Lab2LCh.c
index 25c7ec46..32ec244c 100644
--- a/libvips/colour/im_Lab2LCh.c
+++ b/libvips/colour/im_Lab2LCh.c
@@ -1,12 +1,4 @@
-/* @(#) Turn Lab to LCh
- * @(#) 
- * @(#) Usage: 	
- * @(#) 	im_Lab2LCh( imagein, imageout )
- * @(#) 	IMAGE *imagein, *imageout;
- * @(#) 
- * @(#) Float in, float out.
- * @(#) 
- * @(#) Returns: -1 on error, else 0
+/* Turn Lab to LCh
  */
 
 /*
@@ -75,29 +67,46 @@ imb_Lab2LCh( float *p, float *q, int n )
 	}
 }
 
-int 
-im_Lab2LCh( IMAGE *in, IMAGE *out )
-{	
-	/* Check input image.
-	 */
-	if( in->Bands != 3 || in->BandFmt != IM_BANDFMT_FLOAT || 
-		in->Coding != IM_CODING_NONE ) {
-		im_error( "im_Lab2LCh", "%s", 
-			_( "3-band uncoded float input only" ) );
-		return( -1 ); 
-	}
+int
+im__colour_unary( const char *domain,
+	IMAGE *in, IMAGE *out,
+	im_wrapone_fn buffer_fn, void *a, void *b )
+{
+	IMAGE *t[1];
 
-	/* Prepare the output image 
-	 */
-	if( im_cp_desc( out, in ) )
+	if( im_check_uncoded( domain, in ) ||
+		im_check_bands( domain, in, 3 ) ||
+		im_open_local_array( out, t, 1, domain, "p" ) ||
+		im_clip2fmt( in, t[0], IM_BANDFMT_FLOAT ) )
 		return( -1 );
-	out->Type = IM_TYPE_LCH;
 
-	/* Process!
-	 */
-	if( im_wrapone( in, out, 
-		(im_wrapone_fn) imb_Lab2LCh, NULL, NULL ) )
+	if( im_cp_desc( out, t[0] ) )
+		return( -1 );
+
+	if( im_wrapone( t[0], out, 
+		(im_wrapone_fn) buffer_fn, a, b ) )
 		return( -1 );
 
 	return( 0 );
 }
+
+/**
+ * im_Lab2LCh:
+ * @in: input image
+ * @out: output image
+ *
+ * Turn Lab to LCh.
+ *
+ * Returns: 0 on success, -1 on error.
+ */
+int 
+im_Lab2LCh( IMAGE *in, IMAGE *out )
+{
+	if( im__colour_unary( "im_Lab2LCh", in, out, 
+		(im_wrapone_fn) imb_Lab2LCh, NULL, NULL ) )
+		return( -1 );
+
+	out->Type = IM_TYPE_LCH;
+
+	return( 0 );
+}
diff --git a/libvips/colour/im_Lab2LabQ.c b/libvips/colour/im_Lab2LabQ.c
index 807d45f8..db4b0954 100644
--- a/libvips/colour/im_Lab2LabQ.c
+++ b/libvips/colour/im_Lab2LabQ.c
@@ -25,6 +25,9 @@
  *	- go int earlier for speed up
  * 20/6/02 JC
  *	- oops, were not clipping a/b range correctly
+ * 1/11/09
+ *	- gtkdoc
+ *	- cleanups
  */
 
 /*
@@ -125,34 +128,24 @@ imb_Lab2LabQ( float *inp, unsigned char *outbuf, int n )
 }
 
 int
-im_Lab2LabQ( IMAGE *labim, IMAGE *outim )
+im_Lab2LabQ( IMAGE *in, IMAGE *out )
 {
-	/* Check for uncoded Lab type 
-	 */
-	if( labim->Coding != IM_CODING_NONE ) {
-		im_error( "im_Lab2LabQ", "%s", 
-			_( "uncoded input only" ) );
-		return( -1 );
-	}
-	if( labim->BandFmt != IM_BANDFMT_FLOAT || labim->Bands != 3 ) {
-		im_error( "im_Lab2LabQ", "%s", 
-			_( "three-band float input only" ) );
-		return( -1 );
-	}
+	IMAGE *t[1];
 
-	/* Set up output image.
-	 */
-	if( im_cp_desc( outim, labim ) ) 
+	if( im_check_uncoded( "im_Lab2LabQ", in ) ||
+		im_check_bands( "im_Lab2LabQ", in, 3 ) ||
+		im_open_local_array( out, t, 1, "im_Lab2LabQ", "p" ) ||
+		im_clip2fmt( in, t[0], IM_BANDFMT_FLOAT ) )
 		return( -1 );
-	outim->Bands = 4;
-	outim->Type = IM_TYPE_LAB;
-	outim->BandFmt = IM_BANDFMT_UCHAR;
-	outim->Bbits = 8;
-	outim->Coding = IM_CODING_LABQ;
 
-	/* Process.
-	 */
-	if( im_wrapone( labim, outim, 
+	if( im_cp_desc( out, t[0] ) )
+		return( -1 );
+	out->Bands = 4;
+	out->Type = IM_TYPE_LAB;
+	out->BandFmt = IM_BANDFMT_UCHAR;
+	out->Coding = IM_CODING_LABQ;
+
+	if( im_wrapone( t[0], out, 
 		(im_wrapone_fn) imb_Lab2LabQ, NULL, NULL ) )
 		return( -1 );
 
diff --git a/libvips/colour/im_Lab2LabS.c b/libvips/colour/im_Lab2LabS.c
index 56158d04..a391bbf3 100644
--- a/libvips/colour/im_Lab2LabS.c
+++ b/libvips/colour/im_Lab2LabS.c
@@ -1,6 +1,10 @@
-/* @(#) im_Lab2LabS: quantise FLOAT Lab image into signed short format
+/* im_Lab2LabS: quantise FLOAT Lab image into signed short format
+ *
  * 12/12/02 JC
  *	- from im_Lab2LabQ
+ * 1/11/09
+ *	- gtkdoc
+ *	- cleanups
  */
 
 /*
@@ -60,33 +64,33 @@ imb_Lab2LabS( float *in, signed short *out, int n )
 	}
 }
 
+/**
+ * im_Lab2LabS:
+ * @in: input image
+ * @out: output image
+ *
+ * Turn Lab to LabS, signed 16-bit int fixed point.
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 int
-im_Lab2LabS( IMAGE *labim, IMAGE *outim )
+im_Lab2LabS( IMAGE *in, IMAGE *out )
 {
-	/* Check for uncoded Lab type 
-	 */
-	if( labim->Coding != IM_CODING_NONE ) {
-		im_error( "im_Lab2LabS", "%s", 
-			_( "uncoded input only" ) );
-		return( -1 );
-	}
-	if( labim->BandFmt != IM_BANDFMT_FLOAT || labim->Bands != 3 ) {
-		im_error( "im_Lab2LabS", "%s", 
-			_( "three-band float input only" ) );
-		return( -1 );
-	}
+	IMAGE *t[1];
 
-	/* Set up output image.
-	 */
-	if( im_cp_desc( outim, labim ) ) 
+	if( im_check_uncoded( "im_Lab2LabS", in ) ||
+		im_check_bands( "im_Lab2LabS", in, 3 ) ||
+		im_open_local_array( out, t, 1, "im_Lab2LabS", "p" ) ||
+		im_clip2fmt( in, t[0], IM_BANDFMT_FLOAT ) )
 		return( -1 );
-	outim->Type = IM_TYPE_LABS;
-	outim->BandFmt = IM_BANDFMT_SHORT;
-	outim->Bbits = IM_BBITS_SHORT;
 
-	/* Process.
-	 */
-	if( im_wrapone( labim, outim, 
+	if( im_cp_desc( out, t[0] ) )
+		return( -1 );
+	out->Type = IM_TYPE_LABS;
+	out->BandFmt = IM_BANDFMT_SHORT;
+	out->Bbits = IM_BBITS_SHORT;
+
+	if( im_wrapone( t[0], out, 
 		(im_wrapone_fn) imb_Lab2LabS, NULL, NULL ) )
 		return( -1 );
 
diff --git a/libvips/colour/im_LabQ2disp.c b/libvips/colour/im_LabQ2disp.c
index 85b84fe6..2a18626a 100644
--- a/libvips/colour/im_LabQ2disp.c
+++ b/libvips/colour/im_LabQ2disp.c
@@ -59,7 +59,6 @@
  */
 typedef struct {
         struct im_col_display *disp;
-        struct im_col_tab_disp *dtab;
         PEL red[ 64 * 64 * 64 ];
         PEL green[ 64 * 64 * 64 ];
         PEL blue[ 64 * 64 * 64 ];
@@ -130,11 +129,6 @@ im_LabQ2disp_build_table( IMAGE *out, struct im_col_display *d )
         if( !(cal = IM_NEW( out, CalibrateInfo )) )
                 return( NULL );
         cal->disp = d;
-        if( !(cal->dtab = im_col_make_tables_RGB( out, d ) ) ) {
-		if( !out )
-			im_free( cal );
-                return( NULL );
-	}
 
         /* Build our tables.
          */
@@ -156,7 +150,7 @@ im_LabQ2disp_build_table( IMAGE *out, struct im_col_display *d )
 
                                 /* Convert to display. 
                                  */
-                                im_col_XYZ2rgb( cal->disp, cal->dtab,
+                                im_col_XYZ2rgb( cal->disp, 
                                         X, Y, Z, &rb, &gb, &bb, &oflow );
 
 				/* Save RGB.
diff --git a/libvips/colour/im_XYZ2disp.c b/libvips/colour/im_XYZ2disp.c
index 335ff1c7..a49de02a 100644
--- a/libvips/colour/im_XYZ2disp.c
+++ b/libvips/colour/im_XYZ2disp.c
@@ -68,14 +68,15 @@
 /* Process a buffer of data.
  */
 void
-imb_XYZ2disp( float *p, PEL *q, int n, 
-	struct im_col_tab_disp *table, struct im_col_display *d )
-{		
-	int x;
+imb_XYZ2disp( float *p, PEL *q, int n, struct im_col_display *d )
+{
+	struct im_col_tab_disp *table = im_col_display_get_table( d );
 	float rstep = (d->d_YCR - d->d_Y0R) / 1500.0;
 	float gstep = (d->d_YCG - d->d_Y0G) / 1500.0;
 	float bstep = (d->d_YCB - d->d_Y0B) / 1500.0;
 
+	int x;
+
 	for( x = 0; x < n; x++ ) {
 		float Yr, Yg, Yb;
 		int i;
@@ -133,8 +134,6 @@ imb_XYZ2disp( float *p, PEL *q, int n,
 int 
 im_XYZ2disp( IMAGE *in, IMAGE *out, struct im_col_display *d )
 {	
-	struct im_col_tab_disp *table;
-
 	/* Check input image.
 	 */
 	if( in->Bands != 3 || in->BandFmt != IM_BANDFMT_FLOAT || 
@@ -150,15 +149,10 @@ im_XYZ2disp( IMAGE *in, IMAGE *out, struct im_col_display *d )
 	out->BandFmt = IM_BANDFMT_UCHAR;
 	out->Type = IM_TYPE_RGB;
 
-	/* Build the lookup tables
-	 */
-	if( !(table = im_col_make_tables_RGB( out, d )) )
-		return( -1 );
-
 	/* Do the processing.
 	 */
 	if( im_wrapone( in, out, 
-		(im_wrapone_fn) imb_XYZ2disp, table, d ) )
+		(im_wrapone_fn) imb_XYZ2disp, d, NULL ) )
 		return( -1 );
 
 	return( 0 );
diff --git a/libvips/colour/im_dE00_fromLab.c b/libvips/colour/im_dE00_fromLab.c
index 142fbd55..55ea9aea 100644
--- a/libvips/colour/im_dE00_fromLab.c
+++ b/libvips/colour/im_dE00_fromLab.c
@@ -45,11 +45,11 @@
 #include <dmalloc.h>
 #endif /*WITH_DMALLOC*/
 
-/* An n-input colour operation. Cast the inputs to three-band float and call.
+/* A colour difference operation.
  */
 int
-im__colour_binary( const char *domain,
-	IMAGE *in1, IMAGE *in2, int bands, IMAGE *out, 
+im__colour_difference( const char *domain,
+	IMAGE *in1, IMAGE *in2, IMAGE *out, 
 	im_wrapmany_fn buffer_fn, void *a, void *b )
 {
 	IMAGE *t[3];
@@ -66,7 +66,8 @@ im__colour_binary( const char *domain,
 
 	if( im_cp_descv( out, t[0], t[1], NULL ) )
 		return( -1 );
-	out->Bands = bands;
+	out->Bands = 1;
+	out->Type = IM_TYPE_B_W;
 
 	t[2] = NULL;
 	if( im_wrapmany( t, out, buffer_fn, a, b ) )
@@ -112,12 +113,7 @@ imb_dE00_fromLab( float **p, float *q, int n )
 int 
 im_dE00_fromLab( IMAGE *in1, IMAGE *in2, IMAGE *out )
 {
-	if( im__colour_binary( "im_dE00_fromLab",
-		in1, in2, 1, out, 
-		(im_wrapmany_fn) imb_dE00_fromLab, NULL, NULL ) )
-		return( -1 );
-
-	out->Type = IM_TYPE_B_W;
-
-	return( 0 );
+	return( im__colour_difference( "im_dE00_fromLab",
+		in1, in2, out, 
+		(im_wrapmany_fn) imb_dE00_fromLab, NULL, NULL ) );
 }
diff --git a/libvips/colour/im_dECMC_fromLab.c b/libvips/colour/im_dECMC_fromLab.c
index 072b8968..fe2601c5 100644
--- a/libvips/colour/im_dECMC_fromLab.c
+++ b/libvips/colour/im_dECMC_fromLab.c
@@ -82,12 +82,7 @@ imb_dECMC_fromLab( float **p, float *q, int n )
 int 
 im_dECMC_fromLab( IMAGE *in1, IMAGE *in2, IMAGE *out )
 {
-	if( im__colour_binary( "im_dECMC_fromLab",
-		in1, in2, 1, out, 
-		(im_wrapmany_fn) imb_dECMC_fromLab, NULL, NULL ) )
-		return( -1 );
-
-	out->Type = IM_TYPE_B_W;
-
-	return( 0 );
+	return( im__colour_difference( "im_dECMC_fromLab",
+		in1, in2, out, 
+		(im_wrapmany_fn) imb_dECMC_fromLab, NULL, NULL ) );
 }
diff --git a/libvips/colour/im_dE_fromLab.c b/libvips/colour/im_dE_fromLab.c
index 63fba96d..179a3fe9 100644
--- a/libvips/colour/im_dE_fromLab.c
+++ b/libvips/colour/im_dE_fromLab.c
@@ -77,12 +77,7 @@ imb_dE_fromLab( float **p, float *q, int n )
 int 
 im_dE_fromLab( IMAGE *in1, IMAGE *in2, IMAGE *out )
 {
-	if( im__colour_binary( "im_dE_fromLab",
-		in1, in2, 1, out, 
-		(im_wrapmany_fn) imb_dE_fromLab, NULL, NULL ) )
-		return( -1 );
-
-	out->Type = IM_TYPE_B_W;
-
-	return( 0 );
+	return( im__colour_difference( "im_dE_fromLab",
+		in1, in2, out, 
+		(im_wrapmany_fn) imb_dE_fromLab, NULL, NULL ) );
 }
diff --git a/libvips/colour/im_disp2XYZ.c b/libvips/colour/im_disp2XYZ.c
index 5e692d8d..37c8ee8f 100644
--- a/libvips/colour/im_disp2XYZ.c
+++ b/libvips/colour/im_disp2XYZ.c
@@ -59,8 +59,7 @@
 /* Convert a buffer.
  */
 void
-imb_disp2XYZ( PEL *p, float *q, int n, 
-	struct im_col_display *d, struct im_col_tab_disp *table )
+imb_disp2XYZ( PEL *p, float *q, int n, struct im_col_display *d )
 {
 	int x;
 
@@ -71,7 +70,7 @@ imb_disp2XYZ( PEL *p, float *q, int n,
 		float X, Y, Z;
 		p += 3;
 
-		im_col_rgb2XYZ(d, table, r, g, b, &X, &Y, &Z);
+		im_col_rgb2XYZ( d, r, g, b, &X, &Y, &Z );
 
 		q[0] = X;
 		q[1] = Y;
@@ -83,8 +82,6 @@ imb_disp2XYZ( PEL *p, float *q, int n,
 int 
 im_disp2XYZ( IMAGE *in, IMAGE *out, struct im_col_display *d )
 {	
-	struct im_col_tab_disp *table; /* pointer to the lookup tables */
-
 	/* Check input image.
 	 */
 	if( in->Bands != 3 || in->BandFmt != IM_BANDFMT_UCHAR || 
@@ -102,14 +99,10 @@ im_disp2XYZ( IMAGE *in, IMAGE *out, struct im_col_display *d )
 	out->BandFmt = IM_BANDFMT_FLOAT;
 	out->Type = IM_TYPE_XYZ;
 
-	/* Prepare the lookup tables
-	 */
-	table = im_col_make_tables_RGB( out, d );
-
 	/* Do the processing.
 	 */
 	if( im_wrapone( in, out,
-		(im_wrapone_fn) imb_disp2XYZ, d, table ) )
+		(im_wrapone_fn) imb_disp2XYZ, d, NULL ) )
 		return( -1 );
 
 	return( 0 );
diff --git a/libvips/colour/im_float2rad.c b/libvips/colour/im_float2rad.c
index aa06a9f5..eb425ac6 100644
--- a/libvips/colour/im_float2rad.c
+++ b/libvips/colour/im_float2rad.c
@@ -1,4 +1,5 @@
 /* Convert float to Radiance 32bit packed format
+ *
  * 23/3/09
  * 	- from im_rad2float and Radiance sources
  */
@@ -180,26 +181,33 @@ float2rad( COLOR *inp, COLR *outbuf, int n )
 	}
 }
 
+/**
+ * im_float2rad:
+ * @in: input image
+ * @out: output image
+ *
+ * Convert float to Radiance 32bit packed format.
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 int
 im_float2rad( IMAGE *in, IMAGE *out )
 {
-	/* Must be 3-band float.
-	 */
-	if( in->Bands != 3 || in->BandFmt != IM_BANDFMT_FLOAT ||
-		in->Coding != IM_CODING_NONE ) {
-		im_error( "im_float2rad", "%s",
-			_( "3-band float uncoded only" ) );
-		return( -1 );
-	}
+	IMAGE *t[1];
 
-	if( im_cp_desc( out, in ) )
+	if( im_check_uncoded( "im_float2rad", in ) ||
+		im_check_bands( "im_float2rad", in, 3 ) ||
+		im_open_local_array( out, t, 1, "im_float2rad", "p" ) ||
+		im_clip2fmt( in, t[0], IM_BANDFMT_FLOAT ) )
+		return( -1 );
+
+	if( im_cp_desc( out, t[0] ) )
 		return( -1 );
 	out->Bands = 4;
 	out->BandFmt = IM_BANDFMT_UCHAR;
-	out->Bbits = im_bits_of_fmt( out->BandFmt );
 	out->Coding = IM_CODING_RAD;
 
-	if( im_wrapone( in, out, 
+	if( im_wrapone( t[0], out, 
 		(im_wrapone_fn) float2rad, NULL, NULL ) )
 		return( -1 );
 
diff --git a/libvips/include/vips/colour.h b/libvips/include/vips/colour.h
index 08bbeca3..e54998a0 100644
--- a/libvips/include/vips/colour.h
+++ b/libvips/include/vips/colour.h
@@ -103,7 +103,7 @@ typedef struct {
 /* Colour loading and conversion functions.
  */
 void im_col_ab2Ch( float a, float b, float *C, float *h );
-void im_col_LCh2ab( float L, float C, float h, float *a, float *b );
+void im_col_Ch2ab( float C, float h, float *a, float *b );
 void im_col_XYZ2Lab( float X, float Y, float Z, float *L, float *a, float *b );
 void im_col_Lab2XYZ( float L, float a, float b, float *X, float *Y, float *Z );
 float im_col_pythagoras( float L1, float a1, float b1, 
diff --git a/libvips/include/vips/disp.h b/libvips/include/vips/disp.h
index 225d67d4..d9159f0f 100644
--- a/libvips/include/vips/disp.h
+++ b/libvips/include/vips/disp.h
@@ -50,6 +50,8 @@ enum im_col_disp_type {
  * papers for details on the fields.
  */
 struct im_col_display {
+	/* All private.
+	 */
 	/*< private >*/
 	char *d_name;			/* Display name */
 	enum im_col_disp_type d_type;	/* Display type */
@@ -77,6 +79,8 @@ struct im_col_display {
  * Also holds the luminance to XYZ matrix and the inverse one.
  */
 struct im_col_tab_disp {
+	/* All private.
+	 */
 	/*< private >*/
 	float	t_Yr2r[1501];		/* Conversion of Yr to r */
 	float	t_Yg2g[1501];		/* Conversion of Yg to g */
@@ -93,21 +97,22 @@ struct im_col_tab_disp {
 struct im_col_tab_disp *im_col_make_tables_RGB( 
 	IMAGE *im,
 	struct im_col_display *d );
+struct im_col_tab_disp *im_col_display_get_table( struct im_col_display *d );
+
 int im_col_rgb2XYZ( struct im_col_display *d, 
-	struct im_col_tab_disp *table, 
 	int r, int g, int b, 
 	float *X, float *Y, float *Z );
 int im_col_XYZ2rgb( 
-	struct im_col_display *d, struct im_col_tab_disp *table, 
+	struct im_col_display *d, 
 	float X, float Y, float Z, 
 	int *r_ret, int *g_ret, int *b_ret, 
 	int *or_ret );
 
-int im_XYZ2disp( IMAGE *, IMAGE *, struct im_col_display * );
-int im_Lab2disp( IMAGE *, IMAGE *, struct im_col_display * );
-int im_LabQ2disp( IMAGE *, IMAGE *, struct im_col_display * );
-int im_disp2XYZ( IMAGE *, IMAGE *, struct im_col_display * );
-int im_disp2Lab( IMAGE *, IMAGE *, struct im_col_display * );
+int im_XYZ2disp( IMAGE *in, IMAGE *out, struct im_col_display *d );
+int im_Lab2disp( IMAGE *in, IMAGE *out, struct im_col_display *d );
+int im_LabQ2disp( IMAGE *in, IMAGE *out, struct im_col_display *d );
+int im_disp2XYZ( IMAGE *in, IMAGE *out, struct im_col_display *d );
+int im_disp2Lab( IMAGE *in, IMAGE *out, struct im_col_display *d );
 
 /* Colour display values and arrays
 	&im_col_screen_white,	index 0
@@ -119,14 +124,16 @@ int im_disp2Lab( IMAGE *, IMAGE *, struct im_col_display * );
 	&ultra2,		index 6 
 	&srgb_profile,		index 7 
  */
-struct im_col_display *im_col_displays( int );
-struct im_col_display *im_col_display_name( const char * );
+struct im_col_display *im_col_displays( int n );
+struct im_col_display *im_col_display_name( const char *name );
 
 void *im_LabQ2disp_build_table( IMAGE *out, struct im_col_display *d );
 int im_LabQ2disp_table( IMAGE *in, IMAGE *out, void *table );
 
-int im_dE_fromdisp( IMAGE *, IMAGE *, IMAGE *, struct im_col_display * );
-int im_dECMC_fromdisp( IMAGE *, IMAGE *, IMAGE *, struct im_col_display * );
+int im_dE_fromdisp( IMAGE *in1, IMAGE *in2, IMAGE *out, 
+	struct im_col_display *d );
+int im_dECMC_fromdisp( IMAGE *in1, IMAGE *in2, IMAGE *out, 
+	struct im_col_display *d );
 
 #ifdef __cplusplus
 }
diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
index 7c70006a..45002c4f 100644
--- a/libvips/include/vips/internal.h
+++ b/libvips/include/vips/internal.h
@@ -163,9 +163,15 @@ typedef int (*im__wrapscan_fn)( void *p, int n, void *seq, void *a, void *b );
 int im__wrapscan( IMAGE *in, 
 	im_start_fn start, im__wrapscan_fn scan, im_stop_fn stop,
 	void *a, void *b );
-int im__colour_binary( const char *domain,
-	IMAGE *in1, IMAGE *in2, int bands, IMAGE *out, 
+int im__colour_difference( const char *domain,
+	IMAGE *in1, IMAGE *in2, IMAGE *out, 
 	im_wrapmany_fn buffer_fn, void *a, void *b );
+int im__colour_binary( const char *domain,
+	IMAGE *in1, IMAGE *in2, IMAGE *out, 
+	im_wrapmany_fn buffer_fn, void *a, void *b );
+int im__colour_unary( const char *domain,
+	IMAGE *in, IMAGE *out,
+	im_wrapone_fn buffer_fn, void *a, void *b );
 
 int im__test_kill( IMAGE *im );
 void *im__mmap( int fd, int writeable, size_t length, gint64 offset );