better colourspace sniffing

TODO

@@ -3,15 +3,6 @@
 
 - add mono as a colourspace? also rad?
 
-- something to test if an image is in a supported colourspace?
-
-  at the moment we only look at interpretation, but for things like labq 
-  we should check coding too
-
-  labs needs more checks than that
-
-  _RGB and _sRGB as well
-
   move colour_convert into a separate file
 
 - im_icc_ac2rc needs doing once we have a general 'convert' operator

libvips/colour/colour.c

@@ -709,6 +709,8 @@ vips_colour_convert_build( VipsObject *object )
 	VipsImage *x;
 	VipsImage **t;
 
+	VipsInterpretation interpretation;
+
 	t = (VipsImage **) vips_object_local_array( object, MAX_STEPS );
 
 	/* Verify that all input args have been set.
@@ -717,9 +719,11 @@ vips_colour_convert_build( VipsObject *object )
 		build( object ) )
 		return( -1 );
 
+	interpretation = vips_image_guess_interpretation( convert->in );
+
 	/* No conversion necessary.
 	 */
-	if( convert->in->Type == convert->space ) {
+	if( interpretation == convert->space ) {
 		g_object_set( convert, "out", vips_image_new(), NULL ); 
 
 		return( vips_image_write( convert->in, convert->out ) );
@@ -728,13 +732,14 @@ vips_colour_convert_build( VipsObject *object )
 	x = convert->in;
 
 	for( i = 0; i < VIPS_NUMBER( vips_colour_routes ); i++ )
-		if( vips_colour_routes[i].from == x->Type &&
+		if( vips_colour_routes[i].from == interpretation &&
 			vips_colour_routes[i].to == convert->space )
 			break;
 	if( i == VIPS_NUMBER( vips_colour_routes ) ) {
 		vips_error( "vips_colour_convert", 
 			_( "no known route between '%s' and '%s'" ),
-			vips_enum_nick( VIPS_TYPE_INTERPRETATION, x->Type ),
+			vips_enum_nick( VIPS_TYPE_INTERPRETATION, 
+				interpretation ),
 			vips_enum_nick( VIPS_TYPE_INTERPRETATION, 
 				convert->space ) );
 		return( -1 );

libvips/include/vips/header.h

@@ -85,6 +85,7 @@ int vips_image_get_bands( const VipsImage *image );
 VipsBandFormat vips_image_get_format( const VipsImage *image );
 VipsCoding vips_image_get_coding( const VipsImage *image );
 VipsInterpretation vips_image_get_interpretation( const VipsImage *image );
+VipsInterpretation vips_image_guess_interpretation( const VipsImage *image );
 double vips_image_get_xres( const VipsImage *image );
 double vips_image_get_yres( const VipsImage *image );
 int vips_image_get_xoffset( const VipsImage *image );

libvips/iofuncs/header.c

@@ -364,12 +364,133 @@ vips_image_get_coding( const VipsImage *image )
 	return( image->Coding );
 }
 
+/* vips_image_get_interpretation:
+ * @image: image to guess for
+ *
+ * Return the #VipsInterpretation set in the image header.
+ * Use vips_image_guess_interpretation() is you want a sanity-checked value.
+ *
+ * Returns: the #VipsInterpretation from the image header.
+ */
 VipsInterpretation
 vips_image_get_interpretation( const VipsImage *image )
 {
 	return( image->Type );
 }
 
+/* Try to pick a sane value for interpretation, assuming Type has been set
+ * incorrectly.
+ */
+static VipsInterpretation
+vips_image_default_interpretation( const VipsImage *image )
+{
+	switch( image->Coding ) {
+	case VIPS_CODING_LABQ:
+		return( VIPS_INTERPRETATION_LABQ );
+	case VIPS_CODING_RAD:
+		return( VIPS_INTERPRETATION_RGB );
+	default:
+		break;
+	}
+
+	if( image->Bands == 1 )
+		return( VIPS_INTERPRETATION_B_W );
+	else
+		return( VIPS_INTERPRETATION_MULTIBAND );
+}
+
+/* vips_image_guess_interpretation:
+ * @image: image to guess for
+ *
+ * Return the #VipsInterpretation for an image, guessing a default value if
+ * the set value looks wrong.
+ *
+ * Returns: a sensible #VipsInterpretation for the image.
+ */
+VipsInterpretation
+vips_image_guess_interpretation( const VipsImage *image )
+{
+	gboolean sane;
+
+	sane = TRUE;
+	switch( image->Type ) {
+
+	case VIPS_INTERPRETATION_MULTIBAND: 
+		if( image->Bands == 1 )
+			sane = FALSE;
+		break;
+
+	case VIPS_INTERPRETATION_B_W: 
+		if( image->Bands > 1 )
+			sane = FALSE;
+		break;
+
+	case VIPS_INTERPRETATION_HISTOGRAM: 
+		if( image->Xsize > 1 && image->Ysize > 1 )
+			sane = FALSE;
+		break;
+
+	case VIPS_INTERPRETATION_FOURIER: 
+		if( !vips_band_format_iscomplex( image->BandFmt ) )
+			sane = FALSE;
+		break;
+
+	case VIPS_INTERPRETATION_XYZ: 
+	case VIPS_INTERPRETATION_LAB: 
+	case VIPS_INTERPRETATION_RGB: 
+	case VIPS_INTERPRETATION_CMC: 
+	case VIPS_INTERPRETATION_LCH: 
+	case VIPS_INTERPRETATION_sRGB: 
+	case VIPS_INTERPRETATION_YXY: 
+		if( image->Bands < 3 )
+			sane = FALSE;
+		break;
+
+	case VIPS_INTERPRETATION_CMYK: 
+		if( image->Bands < 4 )
+			sane = FALSE;
+		break;
+
+	case  VIPS_INTERPRETATION_LABQ:
+		if( image->Coding != VIPS_CODING_LABQ )
+			sane = FALSE;
+		break;
+
+	case  VIPS_INTERPRETATION_LABS:
+		if( image->BandFmt != VIPS_FORMAT_SHORT )
+			sane = FALSE;
+		break;
+
+	case  VIPS_INTERPRETATION_RGB16:
+		if( image->BandFmt == VIPS_FORMAT_CHAR ||
+			image->BandFmt == VIPS_FORMAT_UCHAR ||
+			image->Bands < 3 )
+			sane = FALSE;
+		break;
+
+	case  VIPS_INTERPRETATION_GREY16:
+		if( image->BandFmt == VIPS_FORMAT_CHAR ||
+			image->BandFmt == VIPS_FORMAT_UCHAR )
+			sane = FALSE;
+		break;
+
+	case  VIPS_INTERPRETATION_ARRAY:
+		if( image->Bands != 1 )
+			sane = FALSE;
+		break;
+	
+	default:
+		g_assert( 0 );
+		sane = FALSE;
+		break;
+	}
+
+	if( sane )
+		return( vips_image_get_interpretation( image ) );
+	else
+		return( vips_image_default_interpretation( image ) );
+}
+
 double
 vips_image_get_xres( const VipsImage *image )
 {