drop incompatible profiles from save

libpng has started throwing hard errors if the profile does not match
the image -- this can happen all the time with perofiles inherited from
images that have been processed.

Test profiles before save and drop them (with a warning) if they are
incompatible with the image.

ChangeLog

@@ -9,6 +9,7 @@
 - add vips_rotate() ... a convenience method for vips_similarity()
 - svgload was missing is_a [lovell]
 - better header sniffing for small files
+- drop incompatible ICC profiles before save
 
 12/3/18 started 8.6.4
 - better fitting of fonts with overhanging edges, thanks Adrià 

libvips/colour/icc_transform.c

@@ -1226,6 +1226,36 @@ vips_icc_ac2rc( VipsImage *in, VipsImage **out, const char *profile_filename )
 	return( 0 );
 }
 
+/* TRUE if a profile is compatible with an image.
+ */
+gboolean
+vips_icc_is_compatible_profile( VipsImage *image, 
+	void *data, size_t data_length )
+{
+	cmsHPROFILE profile;
+
+	if( !(profile = cmsOpenProfileFromMem( data, data_length )) ) {
+		g_warning( "%s", _( "corrupt profile" ) );
+		return( FALSE ); 
+	}
+
+	if( vips_image_expected_bands( image ) != 
+		vips_icc_profile_needs_bands( profile ) ) {
+		VIPS_FREEF( cmsCloseProfile, profile );
+		g_warning( "%s", 
+			_( "profile incompatible with image" ) );
+		return( FALSE );
+	}
+	if( vips_image_expected_sig( image ) != cmsGetColorSpace( profile ) ) {
+		VIPS_FREEF( cmsCloseProfile, profile );
+		g_warning( "%s", 
+			_( "profile colourspace differs from image" ) );
+		return( FALSE );
+	}
+
+	return( TRUE );
+}
+
 #else /*!HAVE_LCMS2*/
 
 #include <vips/vips.h>
@@ -1245,6 +1275,13 @@ vips_icc_ac2rc( VipsImage *in, VipsImage **out, const char *profile_filename )
 	return( -1 );
 }
 
+gboolean
+vips_icc_is_compatible_profile( VipsImage *image, 
+	void *data, size_t data_length )
+{
+	return( TRUE ); 
+}
+
 #endif /*HAVE_LCMS*/
 
 /**

libvips/foreign/foreign.c

@@ -22,6 +22,8 @@
  * 	- META_SEQ support moved here
  * 5/3/18
  * 	- block _start if one start fails, see #893
+ * 1/4/18
+ * 	- drop incompatible ICC profiles before save
  */
 
 /*
@@ -1504,6 +1506,21 @@ vips__foreign_convert_saveable( VipsImage *in, VipsImage **ready,
 		in = out;
 	}
 
+	/* Some format libraries, like libpng, will throw a hard error if the 
+	 * profile is inappropriate for this image type. With profiles inherited
+	 * from a source image, this can happen all the time, so we 
+	 * want to just drop the profile in this case.
+	 */
+	if( vips_image_get_typeof( in, VIPS_META_ICC_NAME ) ) {
+		void *data;
+		size_t length;
+
+		if( !vips_image_get_blob( in, VIPS_META_ICC_NAME, 
+			&data, &length ) &&
+			!vips_icc_is_compatible_profile( in, data, length ) ) 
+			vips_image_remove( in, VIPS_META_ICC_NAME );
+	}
+
 	*ready = in;
 
 	return( 0 );

libvips/foreign/vipspng.c

@@ -992,7 +992,8 @@ write_vips( Write *write,
 	/* If we're an intel byte order CPU and this is a 16bit image, we need
 	 * to swap bytes.
 	 */
-	if( bit_depth > 8 && !vips_amiMSBfirst() ) 
+	if( bit_depth > 8 && 
+		!vips_amiMSBfirst() ) 
 		png_set_swap( write->pPng ); 
 
 	if( interlace )	

libvips/include/vips/colour.h

@@ -177,6 +177,8 @@ int vips_icc_export( VipsImage *in, VipsImage **out, ... )
 	__attribute__((sentinel));
 int vips_icc_ac2rc( VipsImage *in, VipsImage **out, 
 	const char *profile_filename );
+gboolean vips_icc_is_compatible_profile( VipsImage *image, 
+	void *data, size_t data_length );
 
 int vips_dE76( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 	__attribute__((sentinel));