libvips · jcupitt · Nov 3, 2024 · Nov 1, 2024 · Nov 1, 2024 · Nov 2, 2024
diff --git a/ChangeLog b/ChangeLog
@@ -1,5 +1,7 @@
 8.17.0
 
+- add Magic Kernel support [akimon658]
+
 8.16.1
 
 - support multipage JXL

diff --git a/libvips/include/vips/resample.h b/libvips/include/vips/resample.h
@@ -45,6 +45,8 @@ typedef enum {
 	VIPS_KERNEL_MITCHELL,
 	VIPS_KERNEL_LANCZOS2,
 	VIPS_KERNEL_LANCZOS3,
+	VIPS_KERNEL_MKS2013,
+	VIPS_KERNEL_MKS2021,
 	VIPS_KERNEL_LAST
 } VipsKernel;
 

diff --git a/libvips/resample/reduce.c b/libvips/resample/reduce.c
@@ -66,6 +66,8 @@
  * @VIPS_KERNEL_MITCHELL: Convolve with a Mitchell kernel.
  * @VIPS_KERNEL_LANCZOS2: Convolve with a two-lobe Lanczos kernel.
  * @VIPS_KERNEL_LANCZOS3: Convolve with a three-lobe Lanczos kernel.
+ * @VIPS_KERNEL_MKS2013: Convolve with Magic Kernel Sharp 2013.
+ * @VIPS_KERNEL_MKS2021: Convolve with Magic Kernel Sharp 2021.
  *
  * The resampling kernels vips supports. See vips_reduce(), for example.
  */

diff --git a/libvips/resample/reduceh.cpp b/libvips/resample/reduceh.cpp
@@ -125,6 +125,12 @@ vips_reduce_get_points(VipsKernel kernel, double shrink)
 	case VIPS_KERNEL_LANCZOS3:
 		return 2 * rint(3 * shrink) + 1;
 
+	case VIPS_KERNEL_MKS2013:
+		return 2 * rint(3 * shrink) + 1;
+
+	case VIPS_KERNEL_MKS2021:
+		return 2 * rint(5 * shrink) + 1;
+
 	default:
 		g_assert_not_reached();
 		return 0;

diff --git a/libvips/resample/templates.h b/libvips/resample/templates.h
@@ -402,6 +402,48 @@ double inline filter<VIPS_KERNEL_LANCZOS3>(double x)
 	return 0.0;
 }
 
+template <>
+double inline filter<VIPS_KERNEL_MKS2013>(double x)
+{
+	if (x < 0.0)
+		x = -x;
+
+	if (x >= 2.5)
+		return 0.0;
+
+	if (x >= 1.5)
+		return (x - 5.0 / 2.0) * (x - 5.0 / 2.0) / -8.0;
+
+	if (x >= 0.5)
+		return (4.0 * x * x - 11.0 * x + 7.0) / 4.0;
+
+	return 17.0 / 16.0 - 7.0 * x * x / 4.0;
+}
+
+template <>
+double inline filter<VIPS_KERNEL_MKS2021>(double x)
+{
+	if (x < 0.0)
+		x = -x;
+
+	if (x >= 4.5)
+		return 0.0;
+
+	if (x >= 3.5)
+		return (4.0 * x * x - 36.0 * x + 81.0) / -1152.0;
+
+	if (x >= 2.5)
+		return (4.0 * x * x - 27.0 * x + 45.0) / 144.0;
+
+	if (x >= 1.5)
+		return (24.0 * x * x - 113.0 * x + 130.0) / -144.0;
+
+	if (x >= 0.5)
+		return (140.0 * x * x - 379.0 * x + 239.0) / 144.0;
+
+	return 577.0 / 576.0 - 239.0 * x * x / 144.0;
+}
+
 /* Given an x in [0,1] (we can have x == 1 when building tables),
  * calculate c0 .. c(@n_points), the coefficients. This is called
  * from the interpolator as well as from the table builder.
@@ -469,6 +511,16 @@ vips_reduce_make_mask(T *c, VipsKernel kernel, const int n_points,
 			filter<VIPS_KERNEL_LANCZOS3>, shrink, x);
 		break;
 
+	case VIPS_KERNEL_MKS2013:
+		calculate_coefficients(c, n_points,
+			filter<VIPS_KERNEL_MKS2013>, shrink, x);
+		break;
+
+	case VIPS_KERNEL_MKS2021:
+		calculate_coefficients(c, n_points,
+			filter<VIPS_KERNEL_MKS2021>, shrink, x);
+		break;
+
 	default:
 		g_assert_not_reached();
 		break;

diff --git a/test/test-suite/test_resample.py b/test/test-suite/test_resample.py
@@ -83,7 +83,8 @@ def test_reduce(self):
         for fac in [1, 1.1, 1.5, 1.999]:
             for fmt in all_formats:
                 for kernel in ["nearest", "linear",
-                               "cubic", "lanczos2", "lanczos3"]:
+                               "cubic", "lanczos2",
+                               "lanczos3", "mks2013", "mks2021"]:
                     x = im.cast(fmt)
                     r = x.reduce(fac, fac, kernel=kernel)
                     d = abs(r.avg() - im.avg())
@@ -93,7 +94,8 @@ def test_reduce(self):
         for const in [0, 1, 2, 254, 255]:
             im = (pyvips.Image.black(10, 10) + const).cast("uchar")
             for kernel in ["nearest", "linear",
-                           "cubic", "lanczos2", "lanczos3"]:
+                           "cubic", "lanczos2",
+                           "lanczos3", "mks2013", "mks2021"]:
                 # print "testing kernel =", kernel
                 # print "testing const =", const
                 shr = im.reduce(2, 2, kernel=kernel)