Fixed this years ago and never submitted a patch, silly dropoff fot 10 bit files.

-Steve

Reference: /n/sources/patch/applied/yuv-10bit-oops
Date: Tue Sep 25 15:00:29 CES 2007
Signed-off-by: steve@quintile.net

--- /sys/src/cmd/jpg/readyuv.c	Tue Sep 25 14:59:13 2007
+++ /sys/src/cmd/jpg/readyuv.c	Tue Sep 25 14:59:09 2007
@@ -6,27 +6,12 @@
 #include <ctype.h>
 #include "imagefile.h"
 
-/*
- * ITU/CCIR Rec601 states:
- *
- * R = y + 1.402 * Cr
- * B = Y + 1.77305 * Cb
- * G = Y - 0.72414 * Cr - 0.34414 * Cb
- *
- *	using 8 bit traffic
- * Y = 16 + 219 * Y
- * Cr = 128 + 224 * Cr
- * Cb = 128 + 224 * Cb
- * 	or, if 10bit is used
- * Y = 64 + 876 * Y
- * Cr = 512 + 896 * Cr
- * Cb = 512 + 896 * Cb
- */
 
 enum {
 	pixels = 720,
 	r601pal = 576,
-	r601ntsc = 486
+	r601ntsc = 486,
+	Shift = 13
 };
 
 
@@ -75,7 +60,7 @@
 static int 
 clip(int x)
 {
-	x >>= 18;
+	x >>= (Shift+2); // +2 as we assume all input images are 10 bit
 
 	if (x > 255)
 		return 0xff;
@@ -95,6 +80,7 @@
 	uchar *buf, *r, *g, *b;
 	int y1, y2, cb, cr, c, l, w, base;
 	int bits, lines, pixels;
+	int F1, F2, F3, F4;
 
 	frm = nil;
 	buf = nil;
@@ -161,7 +147,7 @@
 
 			base = l * pixels * 2;
 			for (w = 0; w < pixels * 2; w++)
-				frm[base + w] |= buf[w / 4] >> lsbtab[w % 4];
+				frm[base + w] |= (buf[w / 4] >> lsbtab[w % 4]) & 3;
 		}
 
 	mux = frm;
@@ -170,22 +156,36 @@
 	g = a->chans[1];
 	b = a->chans[2];
 
+	if(pixels * lines != 414720){	// 625
+		F1 = floor(1.402 * (1 << Shift));
+		F2 = floor(0.34414 * (1 << Shift));
+		F3 = floor(0.71414 * (1 << Shift));
+		F4 = floor(1.772 * (1 << Shift));
+	}
+	else{				// 525
+		F1 = floor(1.5748 * (1 << Shift));
+		F2 = floor(0.1874 * (1 << Shift));
+		F3 = floor(0.4681 * (1 << Shift));
+		F4 = floor(1.8560 * (1 << Shift));
+	}
+
 	/*
 	 * Fixme: fixed colourspace conversion at present
 	 */
 	while (mux < end) {
+
 		cb = *mux++ - 512;
-		y1 = (*mux++ - 64) * 76310;
+		y1 = (int)*mux++ << Shift;
 		cr = *mux++ - 512;
-		y2 = (*mux++ - 64) * 76310;
+		y2 = (int)*mux++ << Shift;
 
-		*r++ = clip((104635 * cr) + y1);
-		*g++ = clip((-25690 * cb + -53294 * cr) + y1);
-		*b++ = clip((132278 * cb) + y1);
-
-		*r++ = clip((104635 * cr) + y2);
-		*g++ = clip((-25690 * cb + -53294 * cr) + y2);
-		*b++ = clip((132278 * cb) + y2);
+		*r++ = clip(y1 + F1*cr);
+		*g++ = clip(y1 - F2*cb - F3*cr);
+		*b++ = clip((y1 + F4*cb));
+
+		*r++ = clip(y2 + F1*cr);
+		*g++ = clip(y2 - F2*cb - F3*cr);
+		*b++ = clip((y2 + F4*cb));
 	}
 	free(frm);
 	free(buf);