try making the reduce mask larger with residual

TODO

@@ -1,3 +1,4 @@
+
 - try orc version of reducev? and shrinkv? maybe shrinkh?
 
 

libvips/resample/presample.h

@@ -67,10 +67,11 @@ GType vips_resample_get_type( void );
 
 /* The max size of the vector we use.
  */
-#define MAX_POINTS (6)
+#define MAX_POINTS (50)
 
-int vips_reduce_get_points( VipsKernel kernel );
+int vips_reduce_get_points( VipsKernel kernel, double shrink );
-void vips_reduce_make_mask( VipsKernel kernel, double x, double *c );
+void vips_reduce_make_mask( VipsKernel kernel, double shrink, 
+	double x, double *c );
 
 #ifdef __cplusplus
 }

libvips/resample/reduceh.cpp

@@ -81,8 +81,8 @@ typedef struct _VipsReduceh {
 	 * sizes up to short), and double (for all others). We go to
 	 * scale + 1 so we can round-to-nearest safely.
 	 */
-	int matrixi[VIPS_TRANSFORM_SCALE + 1][MAX_POINTS];
+	int *matrixi[VIPS_TRANSFORM_SCALE + 1];
-	double matrixf[VIPS_TRANSFORM_SCALE + 1][MAX_POINTS];
+	double *matrixf[VIPS_TRANSFORM_SCALE + 1];
 
 } VipsReduceh;
 
@@ -94,10 +94,10 @@ extern "C" {
 G_DEFINE_TYPE( VipsReduceh, vips_reduceh, VIPS_TYPE_RESAMPLE );
 }
 
-/* Get n points.
+/* Get n points. @shrink is the shrink factor, so 2 for a 50% reduction. 
  */
 int
-vips_reduce_get_points( VipsKernel kernel ) 
+vips_reduce_get_points( VipsKernel kernel, double shrink ) 
 {
 	switch( kernel ) {
 	case VIPS_KERNEL_NEAREST:
@@ -110,10 +110,12 @@ vips_reduce_get_points( VipsKernel kernel )
 		return( 4 ); 
 
 	case VIPS_KERNEL_LANCZOS2:
-		return( 4 ); 
+		/* Needs to be in sync with calculate_coefficients_lanczos().
+		 */
+		return( 2 * 2 * ceil( shrink ) + 2 ); 
 
 	case VIPS_KERNEL_LANCZOS3:
-		return( 6 ); 
+		return( 2 * 3 * ceil( shrink ) + 2 ); 
 
 	default:
 		g_assert_not_reached();
@@ -121,10 +123,10 @@ vips_reduce_get_points( VipsKernel kernel )
 	}
 }
 
-/* Calculate a mask.
+/* Calculate a mask element. 
  */
 void
-vips_reduce_make_mask( VipsKernel kernel, double x, double *c )
+vips_reduce_make_mask( VipsKernel kernel, double shrink, double x, double *c )
 {
 	switch( kernel ) {
 	case VIPS_KERNEL_NEAREST:
@@ -141,11 +143,11 @@ vips_reduce_make_mask( VipsKernel kernel, double x, double *c )
 		break;
 
 	case VIPS_KERNEL_LANCZOS2:
-		calculate_coefficients_lanczos( 2, x, c ); 
+		calculate_coefficients_lanczos( 2, shrink, x, c ); 
 		break;
 
 	case VIPS_KERNEL_LANCZOS3:
-		calculate_coefficients_lanczos( 3, x, c ); 
+		calculate_coefficients_lanczos( 3, shrink, x, c ); 
 		break;
 
 	default:
@@ -177,7 +179,7 @@ reduceh_unsigned_int_tab( VipsReduceh *reduceh,
 	}
 }
 
-/* A 4-point interpolation on uint8 is the most common case ... unroll that.
+/* A 6-point interpolation on uint8 is the most common case ... unroll that.
  *
  * The inner loop here won't vectorise, but our inner loop doesn't run for
  * long enough for vectorisation to be useful :-( gcc says it needs about an
@@ -316,7 +318,7 @@ reduceh_notab( VipsReduceh *reduceh,
 
 	double cx[MAX_POINTS];
 
-	vips_reduce_make_mask( reduceh->kernel, x, cx ); 
+	vips_reduce_make_mask( reduceh->kernel, reduceh->xshrink, x, cx ); 
 
 	for( int z = 0; z < bands; z++ ) {
 		out[z] = reduce_sum<T, double>( in, bands, cx, n );
@@ -476,9 +478,23 @@ vips_reduceh_build( VipsObject *object )
 
 	/* Build the tables of pre-computed coefficients.
 	 */
-	reduceh->n_points = vips_reduce_get_points( reduceh->kernel ); 
+	reduceh->n_points = 
+		vips_reduce_get_points( reduceh->kernel, reduceh->xshrink ); 
+	if( reduceh->n_points > MAX_POINTS ) {
+		vips_error( object_class->nickname, 
+			"%s", _( "reduce factor too large" ) );
+		return( -1 );
+	}
 	for( int x = 0; x < VIPS_TRANSFORM_SCALE + 1; x++ ) {
-		vips_reduce_make_mask( reduceh->kernel, 
+		reduceh->matrixf[x] = 
+			VIPS_ARRAY( object, reduceh->n_points, double ); 
+		reduceh->matrixi[x] = 
+			VIPS_ARRAY( object, reduceh->n_points, int ); 
+		if( !reduceh->matrixf[x] ||
+			!reduceh->matrixi[x] )
+			return( -1 ); 
+
+		vips_reduce_make_mask( reduceh->kernel, reduceh->xshrink,
 			(float) x / VIPS_TRANSFORM_SCALE,
 			reduceh->matrixf[x] );
 

libvips/resample/reducev.cpp

@@ -53,10 +53,6 @@
 #include "presample.h"
 #include "templates.h"
 
-/* The max size of the vector we use.
- */
-#define MAX_POINTS (6)
-
 typedef struct _VipsReducev {
 	VipsResample parent_instance;
 
@@ -74,8 +70,8 @@ typedef struct _VipsReducev {
 	 * sizes up to short), and double (for all others). We go to
 	 * scale + 1 so we can round-to-nearest safely.
 	 */
-	int matrixi[VIPS_TRANSFORM_SCALE + 1][MAX_POINTS];
+	int *matrixi[VIPS_TRANSFORM_SCALE + 1];
-	double matrixf[VIPS_TRANSFORM_SCALE + 1][MAX_POINTS];
+	double *matrixf[VIPS_TRANSFORM_SCALE + 1];
 
 } VipsReducev;
 
@@ -243,7 +239,7 @@ reducev_notab( VipsReducev *reducev,
 
 	double cy[MAX_POINTS];
 
-	vips_reduce_make_mask( reducev->kernel, y, cy ); 
+	vips_reduce_make_mask( reducev->kernel, reducev->yshrink, y, cy ); 
 
 	for( int z = 0; z < ne; z++ ) 
 		out[z] = reduce_sum<T, double>( in + z, l1, cy, n );
@@ -379,7 +375,7 @@ vips_reducev_build( VipsObject *object )
 
 	if( reducev->yshrink < 1 ) { 
 		vips_error( object_class->nickname, 
-			"%s", _( "reduce factors should be >= 1" ) );
+			"%s", _( "reduce factor should be >= 1" ) );
 		return( -1 );
 	}
 	if( reducev->yshrink > 3 )  
@@ -391,12 +387,34 @@ vips_reducev_build( VipsObject *object )
 
 	/* Build the tables of pre-computed coefficients.
 	 */
-	reducev->n_points = vips_reduce_get_points( reducev->kernel ); 
+	reducev->n_points = 
+		vips_reduce_get_points( reducev->kernel, reducev->yshrink ); 
+	if( reducev->n_points > MAX_POINTS ) {
+		vips_error( object_class->nickname, 
+			"%s", _( "reduce factor too large" ) );
+		return( -1 );
+	}
 	for( int y = 0; y < VIPS_TRANSFORM_SCALE + 1; y++ ) {
-		vips_reduce_make_mask( reducev->kernel, 
+		reducev->matrixf[y] = 
+			VIPS_ARRAY( object, reducev->n_points, double ); 
+		reducev->matrixi[y] = 
+			VIPS_ARRAY( object, reducev->n_points, int ); 
+		if( !reducev->matrixf[y] ||
+			!reducev->matrixi[y] )
+			return( -1 ); 
+
+		vips_reduce_make_mask( reducev->kernel, reducev->yshrink, 
 			(float) y / VIPS_TRANSFORM_SCALE,
 			reducev->matrixf[y] );
 
+#ifdef DEBUG
+		printf( "vips_reducev_build: masks:\n" ); 
+		printf( "%4g ", (double) y / VIPS_TRANSFORM_SCALE ); 
+		for( int i = 0; i < reducev->n_points; i++ ) 
+			printf( " %4g", reducev->matrixf[y][i] );
+		printf( "\n" ); 
+#endif /*DEBUG*/
+
 		for( int i = 0; i < reducev->n_points; i++ )
 			reducev->matrixi[y][i] = reducev->matrixf[y][i] * 
 				VIPS_INTERPOLATE_SCALE;

libvips/resample/resize.c

@@ -96,8 +96,6 @@ vips_resize_build( VipsObject *object )
 	int int_vshrink;
 	double hresidual;
 	double vresidual;
-	double sigma;
-	gboolean anti_alias;
 
 	if( VIPS_OBJECT_CLASS( vips_resize_parent_class )->build( object ) )
 		return( -1 );
@@ -124,12 +122,12 @@ vips_resize_build( VipsObject *object )
 	if( resize->scale > 1.0 )
 		int_hshrink = 1;
 	else
-		int_hshrink = VIPS_FLOOR( 1.0 / (resize->scale * 1.4) );
+		int_hshrink = VIPS_FLOOR( 1.0 / (resize->scale * 2) );
 	if( vips_object_argument_isset( object, "vscale" ) ) {
 		if( resize->vscale > 1.0 )
 			int_vshrink = 1;
 		else
-			int_vshrink = VIPS_FLOOR( 1.0 / (resize->vscale * 1.4) );
+			int_vshrink = VIPS_FLOOR( 1.0 / (resize->vscale * 2) );
 	}
 	else
 		int_vshrink = int_hshrink;
@@ -202,25 +200,8 @@ vips_resize_build( VipsObject *object )
 		in = t[6];
 	}
 
-	/* If the final affine will be doing a large downsample, we can get 
+	/* Any downsizing.
-	 * nasty aliasing on hard edges. Blur before affine to smooth this out.
-	 *
-	 * Don't blur for very small shrinks, or very small sigma. 
-	 *
-	 * Don't try to be clever for non-rectangular shrinks. We just
-	 * consider the horizontal factor.
 	 */
-	sigma = (1.0 / hresidual) / 2.7; 
-	anti_alias = hresidual < 0.9 && sigma > 0.45;
-	if( anti_alias ) { 
-		vips_info( class->nickname, "anti-alias sigma %g", sigma );
-		if( vips_gaussblur( in, &t[1], sigma, 
-			"min_ampl", 0.1, 
-			NULL ) )
-			return( -1 );
-		in = t[1];
-	}
-
 	if( hresidual < 1.0 || 
 		vresidual < 1.0 ) { 
 		vips_info( class->nickname, "residual reduce by %g x %g", 
@@ -231,6 +212,9 @@ vips_resize_build( VipsObject *object )
 			return( -1 );
 		in = t[2];
 	}
+
+	/* Any upsizing.
+	 */
 	if( hresidual > 1.0 || 
 		vresidual > 1.0 ) { 
 		vips_info( class->nickname, "residual scale %g x %g", 
@@ -242,17 +226,15 @@ vips_resize_build( VipsObject *object )
 		in = t[3];
 	}
 
-	/* If we are upsampling, don't sharpen. Also don't sharpen if we
+	/* If we are upsizing, don't sharpen. 
-	 * skipped the anti-alias filter. 
 	 */
-	if( int_hshrink >= 1 && 
+	if( int_hshrink >= 1 ) { 
-		anti_alias ) { 
 		vips_info( class->nickname, "final sharpen" );
 		t[4] = vips_image_new_matrixv( 3, 3,
 			-1.0, -1.0, -1.0,
-			-1.0, 24.0, -1.0,
+			-1.0, 32.0, -1.0,
 			-1.0, -1.0, -1.0 );
-		vips_image_set_double( t[4], "scale", 16 );
+		vips_image_set_double( t[4], "scale", 24 );
 
 		if( vips_conv( in, &t[5], t[4], NULL ) ) 
 			return( -1 );

libvips/resample/templates.h

@@ -311,17 +311,28 @@ calculate_coefficients_catmull( const double x, double c[4] )
 	c[2] = cthr;
 }
 
-/* Given an offset in [0,1] (we can have x == 1 when building tables),
+/* Given an x in [0,1] (we can have x == 1 when building tables),
- * calculate c0 .. c(a * 2 - 1), the lanczos coefficients. This is called
+ * calculate c0 .. c(@a * @shrink + 1), the lanczos coefficients. This is called
  * from the interpolator as well as from the table builder.
+ *
+ * @a is the number of lobes, so usually 2 or 3. @shrink is the reduction
+ * factor, so 1 for interpolation, 2 for a x2 reduction, etc. We need more
+ * points for large decimations to avoid aliasing. 
  */
 static void inline
-calculate_coefficients_lanczos( int a, const double x, double *c )
+calculate_coefficients_lanczos( const int a, const double shrink, 
+	const double x, double *c )
 {
-	int i;
+	/* Needs to be in sync with vips_reduce_get_points().
+	 */
+	const int n_points = 2 * a * ceil( shrink ) + 2; 
 
-	for( i = 0; i < a * 2; i++ ) {
+	int i;
-		double xp = (i - a) + (1 - x);
+	double sum; 
+
+	sum = 0;
+	for( i = 0; i < n_points; i++ ) {
+		double xp = (i - (n_points - 2) / 2 - x) / shrink;
 
 		double l;
 
@@ -337,7 +348,11 @@ calculate_coefficients_lanczos( int a, const double x, double *c )
 				(VIPS_PI * VIPS_PI * xp * xp);
 
 		c[i] = l;
+		sum += l;
 	}
+
+	for( i = 0; i < n_points; i++ ) 
+		c[i] /= sum;
 }
 
 /* Our inner loop for resampling with a convolution. Operate on elements of 

tools/vipsthumbnail.c

@@ -233,11 +233,11 @@ thumbnail_find_jpegshrink( VipsImage *im )
 	 * doing no further processing, which would make a 400-px version look
 	 * very different from a 450-px version.
 	 */
-	if( shrink >= 9 )
+	if( shrink >= 10 )
 		return( 8 );
-	else if( shrink >= 5 )
+	else if( shrink >= 6 )
 		return( 4 );
-	else if( shrink >= 3 )
+	else if( shrink >= 4 )
 		return( 2 );
 	else 
 		return( 1 );