transform cmyk->rgb automatically

if:

- we are writing a cmyk image
- there is an embedded profile
- the saver does not support cmyk

see https://github.com/jcupitt/libvips/issues/676

ChangeLog

@@ -1,3 +1,7 @@
+12/6/17 started 8.5.7
+- transform cmyk->rgb automatically on write if there's an embedded profile
+  and the saver does not support cmyk
+
 19/5/17 started 8.5.6
 - tiff read with start page > 0 could break edge tiles or strips
 - raise b64 limit to allow for huge profiles (thanks jaume)

configure.ac

@@ -2,7 +2,7 @@
 
 # also update the version number in the m4 macros below
 
-AC_INIT([vips], [8.5.6], [vipsip@jiscmail.ac.uk])
+AC_INIT([vips], [8.5.7], [vipsip@jiscmail.ac.uk])
 # required for gobject-introspection
 AC_PREREQ(2.62)
 
@@ -18,7 +18,7 @@ AC_CONFIG_MACRO_DIR([m4])
 # user-visible library versioning
 m4_define([vips_major_version], [8])
 m4_define([vips_minor_version], [5])
-m4_define([vips_micro_version], [6])
+m4_define([vips_micro_version], [7])
 m4_define([vips_version],
           [vips_major_version.vips_minor_version.vips_micro_version])
 
@@ -38,7 +38,7 @@ VIPS_VERSION_STRING=$VIPS_VERSION-`date`
 #   binary interface changes not backwards compatible?: reset age to 0
 
 LIBRARY_CURRENT=49
-LIBRARY_REVISION=5
+LIBRARY_REVISION=6
 LIBRARY_AGE=7
 
 # patched into include/vips/version.h

libvips/colour/icc_transform.c

@@ -596,6 +596,7 @@ static int
 vips_icc_import_build( VipsObject *object )
 {
 	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object ); 
+	VipsColour *colour = (VipsColour *) object;
 	VipsColourCode *code = (VipsColourCode *) object;
 	VipsIcc *icc = (VipsIcc *) object;
 	VipsIccImport *import = (VipsIccImport *) object;

libvips/foreign/foreign.c

@@ -14,6 +14,8 @@
  * 	- forward progress signals from load
  * 23/5/16
  * 	- remove max-alpha stuff, this is now automatic
+ * 12/6/17
+ * 	- transform cmyk->rgb if there's an embedded profile
  */
 
 /*
@@ -1190,6 +1192,37 @@ vips__foreign_convert_saveable( VipsImage *in, VipsImage **ready,
 		}
 	}
 
+	/* If this image is CMYK and the saver is RGB-only, use lcms to try to
+	 * import to XYZ. This will only work if the image has an embedded
+	 * profile. 
+	 */
+	if( in->Type == VIPS_INTERPRETATION_CMYK &&
+		in->Bands >= 4 &&
+		(saveable == VIPS_SAVEABLE_RGB ||
+		 saveable == VIPS_SAVEABLE_RGBA ||
+		 saveable == VIPS_SAVEABLE_RGBA_ONLY) ) { 
+		VipsImage *out;
+
+		if( vips_icc_import( in, &out, 
+			"pcs", VIPS_PCS_XYZ,
+			NULL ) ) {
+			g_object_unref( in );
+			return( -1 );
+		}
+		g_object_unref( in );
+
+		in = out;
+
+		/* We've imported to PCS, we must remove the embedded profile,
+		 * since it no longer matches the image.
+		 *
+		 * For example, when converting CMYK JPG to RGB PNG, we need 
+		 * to remove the CMYK profile on import, or the png writer will 
+		 * try to attach it when we write the image as RGB.
+		 */
+		vips_image_remove( in, VIPS_META_ICC_NAME );
+	}
+
 	/* If this is something other than CMYK or RAD, eg. maybe a LAB image,
 	 * we need to transform to RGB.
 	 */