fix up XYZ PCS and vipsthumbnail

fix import and export scaling, get vipsthumbnail to use it in --linear
mode

ChangeLog

@@ -19,6 +19,7 @@
 - rename vips_gammacorrect() as vips_gamma(), now takes 1 / exp
 - vips_gamma() works for any format
 - add --linear mode to vipsthumbnail
+- support XYZ as a PCS for vips_icc_import() and vips_icc_export()
 
 18/10/13	started 7.36.3
 - fix compiler warnings in ubuntu 13.10

TODO

@@ -2,14 +2,6 @@
 
 - vipsthumbnail can use vips_conv() now and get rid of the INTMASK
 
-- vips_icc_import() could offer XYZ as well as LAB? it'd save two conversions
-  in vipsthumbnail
-
-  vips_icc_export() would need to be able to accept both types as well
-
-  at the moment, icc_export() assumes LAB, it needs a vips_colourspace() on
-  the input to do an automatic transform for you see vips_dE00() etc. 
-
 - jpegsave needs a --strip option
 
 - jpegsave needs chroma subsampling controls, see:

libvips/colour/icc_transform.c

@@ -24,6 +24,8 @@
  * 	- redo as a class
  * 14/5/13
  * 	- import and export would segv on very wide images
+ * 12/11/13
+ * 	- support XYZ as an alternative PCS
  */
 
 /*
@@ -512,15 +514,19 @@ decode_lab( guint16 *fixed, float *lab, int n )
         }
 }
 
+#define X_FAC (VIPS_D50_X0 * 32768 / (VIPS_D65_X0 * 100))
+#define Y_FAC (VIPS_D50_Y0 * 32768 / (VIPS_D65_Y0 * 100))
+#define Z_FAC (VIPS_D50_Z0 * 32768 / (VIPS_D65_Z0 * 100))
+
 static void 
 decode_xyz( guint16 *fixed, float *xyz, int n )
 {
 	int i;
 
         for( i = 0; i < n; i++ ) {
-                xyz[0] = (double) fixed[0] / 652.800;
+                xyz[0] = (double) fixed[0] / X_FAC;
-                xyz[1] = (double) fixed[1] / 652.800;
+                xyz[1] = (double) fixed[1] / Y_FAC;
-                xyz[2] = (double) fixed[2] / 652.800;
+                xyz[2] = (double) fixed[2] / Z_FAC;
 
                 xyz += 3;
                 fixed += 3;
@@ -623,6 +629,14 @@ vips_icc_export_build( VipsObject *object )
 	VipsIcc *icc = (VipsIcc *) object;
 	VipsIccExport *export = (VipsIccExport *) object;
 
+	/* If icc->pcs hasn't been set and this image is tagged as XYZ, swap
+	 * to XYZ pcs. This will save a XYZ->LAB conversion when we chain up.
+	 */
+	if( !vips_object_argument_isset( object, "pcs" ) &&
+		code->in &&
+		code->in->Type == VIPS_INTERPRETATION_XYZ )  
+		icc->pcs = VIPS_INTERPRETATION_XYZ; 
+
 	if( icc->pcs == VIPS_PCS_LAB ) { 
 #ifdef HAVE_LCMS2
 		cmsCIExyY white;
@@ -741,9 +755,9 @@ encode_xyz( float *xyz, guint16 *fixed, int n )
 		if( Z > MAX_ENCODEABLE_XYZ ) 
 			Z = MAX_ENCODEABLE_XYZ;
 
-		fixed[0] = X * 652.800 + 0.5;
+		fixed[0] = X * X_FAC + 0.5;
-		fixed[1] = Y * 652.800 + 0.5;
+		fixed[1] = Y * Y_FAC + 0.5;
-		fixed[2] = Z * 652.800 + 0.5;
+		fixed[2] = Z * Z_FAC + 0.5;
 
 		xyz += 3;
 		fixed += 3;

tools/vipsthumbnail.c

@@ -349,6 +349,7 @@ thumbnail_shrink( VipsObject *thumbnail, VipsImage *in,
 		if( vips_icc_import( in, &t[1], 
 			"input_profile", import_profile,
 			"embedded", TRUE,
+			"pcs", VIPS_PCS_XYZ,
 			NULL ) )  
 			return( NULL );
 
@@ -419,10 +420,8 @@ thumbnail_shrink( VipsObject *thumbnail, VipsImage *in,
 			vips_image_get_typeof( in, VIPS_META_ICC_NAME ) ) {
 			vips_info( "vipsthumbnail", 
 				"exporting to device space with a profile" );
-			if( vips_colourspace( in, &t[6], 
+			if( vips_icc_export( in, &t[7], 
-				VIPS_INTERPRETATION_LAB, NULL ) ||
+				"output_profile", export_profile,
-				vips_icc_export( t[6], &t[7], 
-					"output_profile", export_profile,
 				NULL ) )  
 				return( NULL );
 			in = t[7];