shithub: hj264

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fix xrgb2yuv420 to use the right BT.709 conversion matrix

the coefficients are those of the digital
sRGB to Y'CbCr color conversion for HDTV,
with the right headroom and footroom,
which can be fairly confusing given all
the different types of "YUV" encodings
available (see https://web.archive.org/web/20180426000512/http://www.equasys.de/colorconversion.html)

--- a/hj264.c

+++ b/hj264.c

@@ -64,8 +64,6 @@

 static uvlong tstart, debug;

 static int opt, noenc;

-static double gamma = 1.0;

-static u8int gammatbl[256];

 #pragma varargck type "ℏ" int

 static int

@@ -225,7 +223,7 @@

 encthread(void *p)

 {

 	u8int *data, v[12], *bgrx;

-	int sz, w, h, x, y;

+	int sz, w, h;

 	Img *img, *prev;

 	uvlong ts;

 	Hj264 *hj;

@@ -247,18 +245,6 @@

 			continue;

 		}

-		if(gamma != 1.0){

-			for(y = 0; y < h; y++){

-				for(x = 0; x < w; x++){

-					bgrx[0] = gammatbl[bgrx[0]];

-					bgrx[1] = gammatbl[bgrx[1]];

-					bgrx[2] = gammatbl[bgrx[2]];

-					bgrx += 4;

-				}

-			}

-			bgrx = img->bgrx;

-		}

-

 		xrgb2yuv420(bgrx, w, h, &hj->yuv);

 		ts = img->ns / Nmsec;

 		if(opt){

@@ -346,7 +332,7 @@

 static void

 usage(void)

 {

-	fprint(2, "usage: %s [-D] [-f FPS] [-F FORMAT] [-g GOP] [-G GAMMA] [-n THREADS] [-o] [-k KBPS] [-q 0…10] [-Q QP] FILE\n", argv0);

+	fprint(2, "usage: %s [-D] [-f FPS] [-F FORMAT] [-g GOP] [-n THREADS] [-o] [-k KBPS] [-q 0…10] [-Q QP] FILE\n", argv0);

 	threadexitsall("usage");

 }

@@ -353,7 +339,7 @@

 int

 main(int argc, char **argv)

 {

-	int i, nthreads, fps, kbps, denoise, quality, qp, gop;

+	int nthreads, fps, kbps, denoise, quality, qp, gop;

 	uvlong fstart, fend, f₀, nframes;

 	char *s, tmp[61], *f[5];

 	int ww₀, hh₀, ww, hh, in, fmt;

@@ -397,9 +383,6 @@

 	case 'g':

 		gop = atoi(EARGF(usage()));

 		break;

-	case 'G':

-		gamma = atof(EARGF(usage()));

-		break;

 	case 'k':

 		kbps = atoi(EARGF(usage()));

 		break;

@@ -432,12 +415,6 @@

 		sysfatal("input: %r");

 	fmtinstall(L'ℏ', hjerror);

-

-	if(gamma != 1.0){

-		gamma = 1.0/gamma;

-		for(i = 0; i < nelem(gammatbl); i++)

-			gammatbl[i] = 255.0*pow((double)i/255.0, gamma);

-	}

 	tmp[60] = 0;

 	if(readn(in, tmp, 60) != 60 || tokenize(tmp, f, 5) != 5)

--- a/yuv.c

+++ b/yuv.c

@@ -2,9 +2,14 @@

 #include <libc.h>

 #include "yuv.h"

-#define Y ((( 54*r + 183*g +  18*b + 128) >> 8) +   0)

+/* ITU-R BT.601 */

+//#define Y ((( 66*r + 129*g +  25*b + 128) >> 8) +  16)

+//#define U (((-38*r -  74*g + 112*b + 128) >> 8) + 128)

+//#define V (((112*r -  94*g -  18*b + 128) >> 8) + 128)

+/* ITU-R BT.709 */

+#define Y ((( 47*r + 157*g +  16*b + 128) >> 8) +  16)

 #define U (((-26*r -  86*g + 112*b + 128) >> 8) + 128)

-#define V (((157*r - 143*g -  14*b + 128) >> 8) + 128)

+#define V (((112*r - 102*g -  10*b + 128) >> 8) + 128)

 void

 xrgb2yuv420(u8int *bgrx, int w, int h, YUV *yuv)