Adds MEAN and MEDIAN methods for region shrink

libvips/foreign/dzsave.c

@@ -1404,7 +1404,7 @@ strip_shrink( Layer *layer )
 		if( vips_rect_isempty( &target ) )
 			break;
 
-		(void) vips_region_shrink( from, to, &target );
+		(void) vips_region_shrink( from, to, &target, VIPS_REGION_SHRINK_MEAN );
 
 		below->write_y += target.height;
 

libvips/foreign/vips2tiff.c

@@ -1392,7 +1392,7 @@ layer_strip_shrink( Layer *layer )
 		if( vips_rect_isempty( &target ) )
 			break;
 
-		(void) vips_region_shrink( from, to, &target );
+		(void) vips_region_shrink( from, to, &target, VIPS_REGION_SHRINK_MEAN );
 
 		below->write_y += target.height;
 

libvips/include/vips/region.h

@@ -55,6 +55,12 @@ extern "C" {
 	(G_TYPE_INSTANCE_GET_CLASS( (obj), \
 	VIPS_TYPE_REGION, VipsRegionClass ))
 
+typedef enum {
+	VIPS_REGION_SHRINK_MEAN,
+	VIPS_REGION_SHRINK_MEDIAN,
+	VIPS_REGION_SHRINK_LAST
+} VipsRegionShrink;
+
 /* Sub-area of image.
  */
 typedef struct _VipsRegion {
@@ -118,7 +124,8 @@ void vips_region_black( VipsRegion *reg );
 void vips_region_copy( VipsRegion *reg, VipsRegion *dest,
 	const VipsRect *r, int x, int y );
 int vips_region_shrink( VipsRegion *from,
-	VipsRegion *to, const VipsRect *target );
+	VipsRegion *to, const VipsRect *target,
+	VipsRegionShrink method );
 
 int vips_region_prepare( VipsRegion *reg, const VipsRect *r );
 int vips_region_prepare_to( VipsRegion *reg,

libvips/iofuncs/region.c

@@ -1166,7 +1166,7 @@ vips_region_shrink_labpack( VipsRegion *from,
 	}
 }
 
-#define SHRINK_TYPE_INT( TYPE ) \
+#define SHRINK_TYPE_MEAN_INT( TYPE ) \
 	for( x = 0; x < target->width; x++ ) { \
 		TYPE *tp = (TYPE *) p; \
 		TYPE *tp1 = (TYPE *) (p + ls); \
@@ -1185,7 +1185,7 @@ vips_region_shrink_labpack( VipsRegion *from,
 		q += ps; \
 	}
 
-#define SHRINK_TYPE_FLOAT( TYPE )  \
+#define SHRINK_TYPE_MEAN_FLOAT( TYPE )  \
 	for( x = 0; x < target->width; x++ ) { \
 		TYPE *tp = (TYPE *) p; \
 		TYPE *tp1 = (TYPE *) (p + ls); \
@@ -1204,10 +1204,30 @@ vips_region_shrink_labpack( VipsRegion *from,
 		q += ps; \
 	}
 
+// This *DOES* gurantee the result is taken from one of the input values
+// It therefore does *NOT* interpolate between the two middle values
+// It is *NOT* stable with respect to the set of values
+// It *IS* however stable with respect to the initial arrangement of values
+#define SHRINK_TYPE_MEDIAN( TYPE ) \
+	for( x = 0; x < target->width; x++ ) { \
+		TYPE *tp = (TYPE *) p; \
+		TYPE *tp1 = (TYPE *) (p + ls); \
+		TYPE *tq = (TYPE *) q; \
+		\
+		for( z = 0; z < nb; z++ ) { \
+            tq[z] = VIPS_MIN( VIPS_MAX( tp[z], tp[z + nb] ), VIPS_MAX( tp1[z], tp1[z + nb] ) ); \
+		} \
+		\
+		/* Move on two pels in input. \
+		 */ \
+		p += ps << 1; \
+		q += ps; \
+	}
+
 /* Generate area @target in @to using pixels in @from. Non-complex.
  */
 static void
-vips_region_shrink_uncoded( VipsRegion *from, 
+vips_region_shrink_uncoded_mean( VipsRegion *from,
 	VipsRegion *to, const VipsRect *target )
 {
 	int ls = VIPS_REGION_LSKIP( from );
@@ -1226,21 +1246,21 @@ vips_region_shrink_uncoded( VipsRegion *from,
 		 */
 		switch( from->im->BandFmt ) {
 		case VIPS_FORMAT_UCHAR:
-			SHRINK_TYPE_INT( unsigned char );  break; 
+			SHRINK_TYPE_MEAN_INT( unsigned char );  break;
 		case VIPS_FORMAT_CHAR:
-			SHRINK_TYPE_INT( signed char );  break; 
+			SHRINK_TYPE_MEAN_INT( signed char );  break;
 		case VIPS_FORMAT_USHORT:
-			SHRINK_TYPE_INT( unsigned short );  break; 
+			SHRINK_TYPE_MEAN_INT( unsigned short );  break;
 		case VIPS_FORMAT_SHORT:
-			SHRINK_TYPE_INT( signed short );  break; 
+			SHRINK_TYPE_MEAN_INT( signed short );  break;
 		case VIPS_FORMAT_UINT:
-			SHRINK_TYPE_INT( unsigned int );  break; 
+			SHRINK_TYPE_MEAN_INT( unsigned int );  break;
 		case VIPS_FORMAT_INT:
-			SHRINK_TYPE_INT( signed int );  break; 
+			SHRINK_TYPE_MEAN_INT( signed int );  break;
 		case VIPS_FORMAT_FLOAT:
-			SHRINK_TYPE_FLOAT( float );  break; 
+			SHRINK_TYPE_MEAN_FLOAT( float );  break;
 		case VIPS_FORMAT_DOUBLE:
-			SHRINK_TYPE_FLOAT( double );  break; 
+			SHRINK_TYPE_MEAN_FLOAT( double );  break;
 
 		default:
 			g_assert_not_reached();
@@ -1248,6 +1268,67 @@ vips_region_shrink_uncoded( VipsRegion *from,
 	}
 }
 
+/* Generate area @target in @to using pixels in @from. Non-complex.
+ */
+static void
+vips_region_shrink_uncoded_median( VipsRegion *from,
+	VipsRegion *to, const VipsRect *target )
+{
+	int ls = VIPS_REGION_LSKIP( from );
+	int ps = VIPS_IMAGE_SIZEOF_PEL( from->im );
+	int nb = from->im->Bands;
+
+	int x, y, z;
+
+	for( y = 0; y < target->height; y++ ) {
+		VipsPel *p = VIPS_REGION_ADDR( from,
+			target->left * 2, (target->top + y) * 2 );
+		VipsPel *q = VIPS_REGION_ADDR( to,
+			target->left, target->top + y );
+
+		/* Process this line of pels.
+		 */
+		switch( from->im->BandFmt ) {
+		case VIPS_FORMAT_UCHAR:
+			SHRINK_TYPE_MEDIAN( unsigned char );  break;
+		case VIPS_FORMAT_CHAR:
+			SHRINK_TYPE_MEDIAN( signed char );  break;
+		case VIPS_FORMAT_USHORT:
+			SHRINK_TYPE_MEDIAN( unsigned short );  break;
+		case VIPS_FORMAT_SHORT:
+			SHRINK_TYPE_MEDIAN( signed short );  break;
+		case VIPS_FORMAT_UINT:
+			SHRINK_TYPE_MEDIAN( unsigned int );  break;
+		case VIPS_FORMAT_INT:
+			SHRINK_TYPE_MEDIAN( signed int );  break;
+		case VIPS_FORMAT_FLOAT:
+			SHRINK_TYPE_MEDIAN( float );  break;
+		case VIPS_FORMAT_DOUBLE:
+			SHRINK_TYPE_MEDIAN( double );  break;
+
+		default:
+			g_assert_not_reached();
+		}
+	}
+}
+
+/* Generate area @target in @to using pixels in @from. Non-complex.
+ */
+static void
+vips_region_shrink_uncoded( VipsRegion *from,
+	VipsRegion *to, const VipsRect *target, VipsRegionShrink method )
+{
+	switch( method ) {
+		case VIPS_REGION_SHRINK_MEAN:
+			vips_region_shrink_uncoded_mean( from, to, target );  break;
+		case VIPS_REGION_SHRINK_MEDIAN:
+			vips_region_shrink_uncoded_median( from, to, target );  break;
+
+		default:
+			g_assert_not_reached();
+	}
+}
+
 /* No point having an int path, this will always be horribly slow.
  */
 #define SHRINK_ALPHA_TYPE( TYPE ) { \
@@ -1336,6 +1417,7 @@ vips_region_shrink_alpha( VipsRegion *from,
  * @from: source region
  * @to: (inout): destination region
  * @target: #VipsRect of pixels you need to copy
+ * @method: #VipsRegionShrink method to use when generating target pixels
  *
  * Write the pixels @target in @to from the x2 larger area in @from.
  * Non-complex uncoded images and LABQ only. Images with alpha (see
@@ -1344,7 +1426,7 @@ vips_region_shrink_alpha( VipsRegion *from,
  * See also: vips_region_copy().
  */
 int
-vips_region_shrink( VipsRegion *from, VipsRegion *to, const VipsRect *target )
+vips_region_shrink( VipsRegion *from, VipsRegion *to, const VipsRect *target, VipsRegionShrink method )
 {
 	VipsImage *image = from->im;
 
@@ -1358,7 +1440,7 @@ vips_region_shrink( VipsRegion *from, VipsRegion *to, const VipsRect *target )
 		if( vips_image_hasalpha( image ) )
 			vips_region_shrink_alpha( from, to, target );
 		else
-			vips_region_shrink_uncoded( from, to, target );
+			vips_region_shrink_uncoded( from, to, target, method );
 	}
 	else
 		vips_region_shrink_labpack( from, to, target );