improve horizontal chroma resolution with pal

Originally committed as revision 22994 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/swscale.c

@@ -2036,7 +2036,10 @@ SwsContext *sws_getContext(int srcW, int srcH, int srcFormat, int dstW, int dstH
 	c->chrSrcVSubSample+= c->vChrDrop;
 
 	// drop every 2. pixel for chroma calculation unless user wants full chroma
-	if((isBGR(srcFormat) || isRGB(srcFormat)) && !(flags&SWS_FULL_CHR_H_INP)) 
+	if((isBGR(srcFormat) || isRGB(srcFormat)) && !(flags&SWS_FULL_CHR_H_INP)
+           && srcFormat!=PIX_FMT_RGB8      && srcFormat!=PIX_FMT_BGR8
+           && srcFormat!=PIX_FMT_RGB4      && srcFormat!=PIX_FMT_BGR4
+           && srcFormat!=PIX_FMT_RGB4_BYTE && srcFormat!=PIX_FMT_BGR4_BYTE)
 		c->chrSrcHSubSample=1;
 
 	if(param){

libswscale/swscale_template.c

@@ -2296,12 +2296,10 @@ static inline void RENAME(palToUV)(uint8_t *dstU, uint8_t *dstV, uint8_t *src1,
         assert(src1 == src2);
 	for(i=0; i<width; i++)
 	{
-		int d0= src1[2*i  ];
-		int d1= src1[2*i+1];
-                int p = (pal[d0]&0xFF00FF) + (pal[d1]&0xFF00FF);
+		int p= pal[src1[i]];
 
-		dstU[i]= (pal[d0]+pal[d1]-p)>>9;
-		dstV[i]= p>>17;
+		dstU[i]= p>>8;
+		dstV[i]= p>>16;
 	}
 }