From: Florian Forster <octo@leeloo.lan.home.verplant.org>
Date: Mon, 20 Aug 2007 10:21:08 +0000 (+0200)
Subject: panolib.c: Use something similar to Lanczos resampling for sharper images.
X-Git-Url: https://git.verplant.org/?a=commitdiff_plain;h=5f375b3cd8a90854793d20f98f1dab67c4708e51;p=libopano.git

panolib.c: Use something similar to Lanczos resampling for sharper images.
---

diff --git a/src/panolib.c b/src/panolib.c
index 6d503d6..58948d3 100644
--- a/src/panolib.c
+++ b/src/panolib.c
@@ -68,6 +68,29 @@ static void set_transformation_matrix (double m[3][3],
 	matrix_matrix_mult( dummy, my, m);
 } /* void SetMatrix */
 
+#if 0
+static double lanczos (double x)
+{
+	static double table[257];
+
+	assert ((x >= 0.0) && (x <= 1.0));
+
+	if (table[0] != 1.0)
+	{
+		int i;
+
+		table[0] = 1.0;
+		for (i = 1; i <= 256; i++)
+		{
+			double t = ((double) i) / 256.0;
+			table[i] = 2 * sin (M_PI * t) * sin (M_PI_2 * t) / (M_PI * M_PI * t * t);
+		}
+	}
+
+	return (table[(int) (0.5 + 256.0 * x)]);
+} /* double lanczos */
+#endif
+
 static int copy_pixel (ui_image_t *dest, const ui_image_t *src,
 		int x_dest, int y_dest,
 		double x_src_fp, double y_src_fp,
@@ -76,7 +99,9 @@ static int copy_pixel (ui_image_t *dest, const ui_image_t *src,
 	uint32_t pixel_dest = (y_dest * dest->width) + x_dest;
 
 	assert (x_src_fp >= 0.0);
-	assert (y_src_fp >= 0.0);
+
+	if (y_src_fp < 0.0)
+		y_src_fp = 0.0;
 
 	if (interp == BILINEAR)
 	{
@@ -101,6 +126,20 @@ static int copy_pixel (ui_image_t *dest, const ui_image_t *src,
 		x_right_frac = x_src_fp - x_src_left;
 		y_bottom_frac = y_src_fp - y_src_top;
 
+		/*
+		 * The polynomial function
+		 *   2x^3 - 3x^2 + 1
+		 * is similar to the Lanczos function, but much easier to compute. It's
+		 * applied here to improve sharpness. 
+		 */
+		{
+			double t = x_src_fp - x_src_left;
+			x_right_frac = -2.0 * t * t * t + 3.0 * t * t;
+
+			t = y_src_fp - y_src_top;
+			y_bottom_frac = -2.0 * t * t * t + 3.0 * t * t;
+		}
+
 		assert ((x_right_frac >= 0.0) && (x_right_frac <= 1.0));
 		assert ((y_bottom_frac >= 0.0) && (y_bottom_frac <= 1.0));