diff --git a/ChangeLog b/ChangeLog
index cd9c78f6..bbc3cae0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -44,8 +44,9 @@
 - renamed im_eor_vec() as im_eorimage_vec() for consistency, also and, or
 - renamed im_eorconst() as im_eorimage_const() for consistency, also and, or
 - relational revised: smaller, more general, faster
-- im_blend() allows many-band conditional, 1-band then/else
-- im_blend() allows band and format to differ between then and else parts
+- im_blend()/im_ifthenelse() allows many-band conditional, 1-band then/else
+- im_blend()/im_ifthenelse() allows band and format to differ between then 
+  and else parts
 
 25/3/09 started 7.18.0
 - revised version numbers
diff --git a/TODO b/TODO
index 1aaa7b80..1e24ed9d 100644
--- a/TODO
+++ b/TODO
@@ -1,11 +1,6 @@
-- do im_ifthenelse
-
-
 - we have tools/ and contrib/ argh
 
 
-
-
 - Joe's new defs
 
 
diff --git a/libvips/include/vips/proto.h b/libvips/include/vips/proto.h
index cfbb03ee..370b1f87 100644
--- a/libvips/include/vips/proto.h
+++ b/libvips/include/vips/proto.h
@@ -136,6 +136,7 @@ int im_isMSBfirst( IMAGE * );
 int im_amiMSBfirst( void );
 
 int im_check_uncoded( const char *domain, IMAGE *im );
+int im_check_known_coded( const char *domain, IMAGE *im );
 int im_check_bands_1orn( const char *domain, IMAGE *im1, IMAGE *im2 );
 int im_check_noncomplex( const char *domain, IMAGE *im );
 int im_check_complex( const char *domain, IMAGE *im );
diff --git a/libvips/iofuncs/predicate.c b/libvips/iofuncs/predicate.c
index 8c0a1dc7..457fb5f5 100644
--- a/libvips/iofuncs/predicate.c
+++ b/libvips/iofuncs/predicate.c
@@ -370,6 +370,21 @@ im_check_uncoded( const char *domain, IMAGE *im )
 	return( 0 );
 }
 
+int
+im_check_known_coded( const char *domain, IMAGE *im )
+{
+	/* These all have codings that extract/ifthenelse/etc can ignore.
+	 */
+	if( im->Coding != IM_CODING_NONE && 
+		im->Coding != IM_CODING_LABQ &&
+		im->Coding != IM_CODING_RAD ) {
+		im_error( domain, "%s", _( "unknown image coding" ) );
+		return( -1 );
+	}
+
+	return( 0 );
+}
+
 int
 im_check_bands_1orn( const char *domain, IMAGE *im1, IMAGE *im2 )
 {
diff --git a/libvips/relational/im_blend.c b/libvips/relational/im_blend.c
index a7bd9837..4dad582d 100644
--- a/libvips/relational/im_blend.c
+++ b/libvips/relational/im_blend.c
@@ -9,6 +9,7 @@
  * 	- gtkdoc comments
  * 	- use im_check*()
  * 	- allow many-band conditional and single-band a/b
+ * 	- allow a/b to differ in format and bands
  */
 
 /*
diff --git a/libvips/relational/im_ifthenelse.c b/libvips/relational/im_ifthenelse.c
index 0c6c566a..48c1d138 100644
--- a/libvips/relational/im_ifthenelse.c
+++ b/libvips/relational/im_ifthenelse.c
@@ -11,6 +11,10 @@
  * 	- set THINSTRIP
  * 23/9/09
  * 	- gtkdoc comment
+ * 23/9/09
+ * 	- use im_check*()
+ * 	- allow many-band conditional and single-band a/b
+ * 	- allow a/b to differ in format and bands
  */
 
 /*
@@ -44,9 +48,8 @@
 #endif /*HAVE_CONFIG_H*/
 #include <vips/intl.h>
 
-#include <stdio.h>
-
 #include <vips/vips.h>
+#include <vips/internal.h>
 
 #ifdef WITH_DMALLOC
 #include <dmalloc.h>
@@ -143,68 +146,24 @@ ifthenelse_gen( REGION *or, void *seq, void *client1, void *client2 )
 	return( 0 );
 }
 
-/**
- * im_ifthenelse:
- * @c: condition #IMAGE
- * @a: then #IMAGE
- * @b: else #IMAGE
- * @out: output #IMAGE
- *
- * This operation scans the condition image @c (which must be unsigned char) 
- * and uses it to select pixels from either the then image @a or the else
- * image @b. Non-zero means @a, 0 means @b.
- *
- * The conditional image @c can have either 1 band, in which case entire pels
- * come either from @a or @b, or n bands, where n is the number of bands in 
- * both @a and @b, in which case individual band elements are chosen from 
- * @a and @b.
- *
- * Images @a and @b must match exactly in size, bands and format.
- *
- * See also: im_blend(), im_equal().
- *
- * Returns: 0 on success, -1 on error
- */
-int
-im_ifthenelse( IMAGE *c, IMAGE *a, IMAGE *b, IMAGE *out )
+static int
+ifthenelse( IMAGE *c, IMAGE *a, IMAGE *b, IMAGE *out )
 {
 	IMAGE **in;
 
 	/* Check args.
 	 */
-	if( a->Coding != IM_CODING_NONE && a->Coding != IM_CODING_LABQ ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "then image must be uncoded or labpack" ) );
-		return( -1 );
-	}
-	if( b->Coding != IM_CODING_NONE && b->Coding != IM_CODING_LABQ ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "else image must be uncoded or labpack" ) );
-		return( -1 );
-	}
-	if( c->Coding != IM_CODING_NONE ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "condition image must be uncoded" ) );
-		return( -1 );
-	}
-	if( a->BandFmt != b->BandFmt ||
-		a->Bands != b->Bands ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "size and format of then and else "
-			"must match" ) );
-		return( -1 );
-	}
-	if( c->BandFmt != IM_BANDFMT_UCHAR ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "conditional image must be uchar" ) );
-		return( -1 );
-	}
-	if( c->Bands != 1 && c->Bands != a->Bands ) {
-		im_error( "im_ifthenelse", 
-			"%s", _( "conditional image must be one band or same "
-			"as then and else images" ) );
-		return( -1 );
-	}
+	if( im_check_uncoded( "im_ifthenelse", c ) ||
+		im_check_uchar( "im_ifthenelse", c ) ||
+		im_check_known_coded( "im_ifthenelse", a ) ||
+		im_check_known_coded( "im_ifthenelse", b ) ||
+		im_check_format( "im_ifthenelse", a, b ) ||
+		im_check_bands( "im_ifthenelse", a, b ) ||
+		im_check_bands_1orn( "im_ifthenelse", c, a ) || 
+		im_piocheck( c, out ) || 
+		im_pincheck( a ) || 
+		im_pincheck( b ) )
+                return( -1 );
 
 	/* Make output image.
 	 */
@@ -218,3 +177,47 @@ im_ifthenelse( IMAGE *c, IMAGE *a, IMAGE *b, IMAGE *out )
 
 	return( 0 );
 }
+
+/**
+ * im_ifthenelse:
+ * @c: condition #IMAGE
+ * @a: then #IMAGE
+ * @b: else #IMAGE
+ * @out: output #IMAGE
+ *
+ * This operation scans the condition image @c (which must be unsigned char) 
+ * and uses it to select pixels from either the then image @a or the else
+ * image @b. Non-zero means @a, 0 means @b.
+ *
+ * Any image can have either 1 band or n bands, where n is the same for all
+ * the non-1-band images. Single band images are then effectively copied to 
+ * make n-band images.
+ *
+ * Images @a and @b are cast up to the smallest common format.
+ *
+ * Images @a and @b must match exactly in size.
+ *
+ * See also: im_blend(), im_equal().
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int
+im_ifthenelse( IMAGE *c, IMAGE *a, IMAGE *b, IMAGE *out )
+{
+	IMAGE *t[7];
+
+	if( im_open_local_array( out, t, 7, "im_ifthenelse", "p" ) )
+		return( -1 );
+
+	/* Make a and b match in bands and format. Don't make c match: we
+	 * special-case this in code above ^^^ for speed.
+	 */
+	if( im__formatalike( a, b, t[0], t[1] ) ||
+		im__bandalike( t[0], t[1], t[2], t[3] ) )
+		return( -1 );
+
+	if( ifthenelse( c, t[2], t[3], out ) )
+		return( -1 );
+
+	return( 0 );
+}