From ba5793d3783dce6c4c048f22b44d33c07f6f5a9c Mon Sep 17 00:00:00 2001
From: Niels Elburg <niels@dyne.org>
Date: Sat, 31 Jul 2004 11:37:30 +0000
Subject: [PATCH] Using weighted averaging for subsampling 2x2 -> 1x1

git-svn-id: svn://code.dyne.org/veejay/trunk@6 eb8d1916-c9e9-0310-b8de-cf0c9472ead5
---
 veejay-30aug04/veejay-0.6/veejay/subsample.c | 58 +++++++++++++++-----
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/veejay-30aug04/veejay-0.6/veejay/subsample.c b/veejay-30aug04/veejay-0.6/veejay/subsample.c
index cc2ec049..d17b7e47 100644
--- a/veejay-30aug04/veejay-0.6/veejay/subsample.c
+++ b/veejay-30aug04/veejay-0.6/veejay/subsample.c
@@ -95,26 +95,58 @@ static void ss_444_to_420jpeg(uint8_t *buffer, int width, int height)
   }
 }
 */
+/*
+
+        using weighted averaging for subsampling 2x2 -> 1x1
+	here, 4 pixels are filled in each inner loop, (weighting
+        16 source pixels)
+*/
 
 static void ss_444_to_420jpeg(uint8_t *buffer, int width, int height)
 {
-  uint8_t *in0, *in1, *out;
-  int x, y;
+  const uint8_t *in0, *in1;
+  uint8_t *out;
+  int x, y = height;
   in0 = buffer;
   in1 = buffer + width;
   out = buffer;
-  for (y = 0; y < height; y += 2) {
-    for (x = 0; x < width; x += 2) {
-      *out = (in0[0] + 3 * (in0[1] + in1[0]) + (9 * in1[1]) + 8) >> 4;
-      in0 += 2;
-      in1 += 2;
-      out++;
-    }
-    in0 += width;
-    in1 += width;
-  }
-}
 
+//  for (y = 0; y < height; y += 2) {
+//    for (x = 0; x < width; x += 2) {
+//     *out = (in0[0] + 3 * (in0[1] + in1[0]) + (9 * in1[1]) + 8) >> 4;
+//      in0 += 2;
+//      in1 += 2;
+//      out++;
+//    }
+//    in0 += width;
+//    in1 += width;
+//  }
+    for(; y > 0; y -- )
+    {
+         in0 = buffer;
+	 in1 = buffer + width;
+	 out = buffer;
+         for( x = width; x >= 4; x -= 4 )
+	 {
+		out[0] = ( in0[0] + 3 * ( in0[1] + in1[0] ) + (9 * in1[1]) + 8) >> 4;
+   		out[1] = ( in0[2] + 3 * ( in0[3] + in1[2] ) + (9 * in1[3]) + 8) >> 4;
+		out[2] = ( in0[4] + 3 * ( in0[5] + in1[4] ) + (9 * in1[5]) + 8) >> 4;
+		out[3] = ( in0[6] + 3 * ( in0[7] + in1[6] ) + (9 * in1[7]) + 8) >> 4;
+		in0 += 8;
+		in1 += 8;
+		out += 4;
+         }
+	 for(; x > 0; x -- )
+	 {
+		out[0] = ( in0[0] + 3 * ( in0[1] + in1[0] ) + (9 * in1[1] ) + 8) >> 4;
+		in0 += 2;
+		in1 += 2;
+		out ++;
+	 }	
+	 buffer += (width << 1);
+	 out    += width;
+    }
+}
 
 
 /* vertical/horizontal interstitial siting