From fdce4f3132f52f5ea550637694f70e037e8a8c3d Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michaelni@gmx.at>
Date: Sun, 6 Jun 2004 13:46:50 +0000
Subject: [PATCH] cubic filter instead of truncated sinc looks much better for
 upscaling & scaling where src and dst size are quite similar

Originally committed as revision 3201 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/imgresample.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libavcodec/imgresample.c b/libavcodec/imgresample.c
index 14fdb1059e..dc5ccf93bd 100644
--- a/libavcodec/imgresample.c
+++ b/libavcodec/imgresample.c
@@ -554,12 +554,18 @@ static void build_filter(int16_t *filter, float factor)
     for(ph=0;ph<NB_PHASES;ph++) {
         norm = 0;
         for(i=0;i<NB_TAPS;i++) {
-            
+#if 1
+            const float d= -0.5; //first order derivative = -0.5
+            x = fabs(((float)(i - FCENTER) - (float)ph / NB_PHASES) * factor);
+            if(x<1.0) y= 1 - 3*x*x + 2*x*x*x + d*(            -x*x + x*x*x);
+            else      y=                       d*(-4 + 8*x - 5*x*x + x*x*x);
+#else
             x = M_PI * ((float)(i - FCENTER) - (float)ph / NB_PHASES) * factor;
             if (x == 0)
                 y = 1.0;
             else
                 y = sin(x) / x;
+#endif
             tab[i] = y;
             norm += y;
         }