Add a quality option to SSDV. Provides 8 quality levels, -4 to 3.

main.c

@@ -26,7 +26,7 @@
 void exit_usage()
 {
 	fprintf(stderr,
-		"Usage: ssdv [-e|-d] [-n] [-t <percentage>] [-c <callsign>] [-i <id>] [<in file>] [<out file>]\n"
+		"Usage: ssdv [-e|-d] [-n] [-t <percentage>] [-c <callsign>] [-i <id>] [-q <level>] [<in file>] [<out file>]\n"
 		"\n"
 		"  -e Encode JPEG to SSDV packets.\n"
 		"  -d Decode SSDV packets to JPEG.\n"
@@ -35,6 +35,7 @@ void exit_usage()
 		"  -t For testing, drops the specified percentage of packets while decoding.\n"
 		"  -c Set the callign. Accepts A-Z 0-9 and space, up to 6 characters.\n"
 		"  -i Set the image ID (0-255).\n"
+		"  -q Set the JPEG quality level (-4 to 3, defaults to 0).\n"
 		"  -v Print data for each packet decoded.\n"
 		"\n");
 	exit(-1);
@@ -52,6 +53,7 @@ int main(int argc, char *argv[])
 	int errors;
 	char callsign[7];
 	uint8_t image_id = 0;
+	int8_t quality;
 	ssdv_t ssdv;
 	
 	uint8_t pkt[SSDV_PKT_SIZE], b[128], *jpeg;
@@ -60,7 +62,7 @@ int main(int argc, char *argv[])
 	callsign[0] = '\0';
 	
 	opterr = 0;
-	while((c = getopt(argc, argv, "ednc:i:t:v")) != -1)
+	while((c = getopt(argc, argv, "ednc:i:q:t:v")) != -1)
 	{
 		switch(c)
 		{
@@ -73,6 +75,7 @@ int main(int argc, char *argv[])
 			strncpy(callsign, optarg, 7);
 			break;
 		case 'i': image_id = atoi(optarg); break;
+		case 'q': quality = atoi(optarg); break;
 		case 't': droptest = atoi(optarg); break;
 		case 'v': verbose = 1; break;
 		case '?': exit_usage();
@@ -166,7 +169,7 @@ int main(int argc, char *argv[])
 		break;
 	
 	case 1: /* Encode */
-		ssdv_enc_init(&ssdv, type, callsign, image_id);
+		ssdv_enc_init(&ssdv, type, callsign, image_id, quality);
 		ssdv_enc_set_buffer(&ssdv, pkt);
 		
 		i = 0;

ssdv.c

@@ -45,6 +45,11 @@ static const uint8_t const sos[10] = {
 0x03,0x01,0x00,0x02,0x11,0x03,0x11,0x00,0x3F,0x00,
 };
 
+/* Quantisation table scaling factors for each quality level 0-7 */
+static const uint16_t const dqt_scales[8] = {
+5000, 357, 172, 116, 100, 58, 28, 0
+};
+
 /* Quantisation tables */
 static const uint8_t const std_dqt0[65] = {
 0x00,0x10,0x0C,0x0C,0x0E,0x0C,0x0A,0x10,0x0E,0x0E,0x0E,0x12,0x12,0x10,0x14,0x18,
@@ -135,6 +140,61 @@ static char *strbits(uint32_t value, uint8_t bits)
 }
 */
 
+static void load_standard_dqt(uint8_t *dst, const uint8_t *table, uint8_t quality)
+{
+	int i;
+	uint16_t scale_factor;
+	uint32_t temp;
+	
+	/* Copy the table ID */
+	*dst++ = *table++;
+	
+	/* Load the scaling factor */
+	if(quality > 7) quality = 7;
+	scale_factor = dqt_scales[quality];
+	
+	/* Copy the remaining 64 coefficients, while applying the scaling factor */
+	for(i = 0; i < 64; i++)
+	{
+		temp = *table++;
+		temp = (temp * scale_factor + 50) / 100;
+		
+		/* limit the values to the valid range */
+		if(temp == 0) temp = 1;
+		if(temp > 255) temp = 255;
+		
+		*dst++ = temp;
+	}
+}
+
+static void *sload_standard_dqt(ssdv_t *s, const uint8_t *table, uint8_t quality)
+{
+	uint8_t *r;
+	
+	/* DQT is 65 bytes long, ensure there is space */
+	if(s->stbl_len + 65 > TBL_LEN + HBUFF_LEN) return(NULL);
+	
+	r = &s->stbls[s->stbl_len];
+	load_standard_dqt(r, table, quality);
+	s->stbl_len += 65;
+	
+	return(r);
+}
+
+static void *dload_standard_dqt(ssdv_t *s, const uint8_t *table, uint8_t quality)
+{
+	uint8_t *r;
+	
+	/* DQT is 65 bytes long, ensure there is space */
+	if(s->dtbl_len + 65 > TBL_LEN + HBUFF_LEN) return(NULL);
+	
+	r = &s->dtbls[s->dtbl_len];
+	load_standard_dqt(r, table, quality);
+	s->dtbl_len += 65;
+	
+	return(r);
+}
+
 static void *stblcpy(ssdv_t *s, const void *src, size_t n)
 {
 	void *r;
@@ -831,18 +891,19 @@ static char ssdv_have_marker_data(ssdv_t *s)
 	return(SSDV_OK);
 }
 
-char ssdv_enc_init(ssdv_t *s, uint8_t type, char *callsign, uint8_t image_id)
+char ssdv_enc_init(ssdv_t *s, uint8_t type, char *callsign, uint8_t image_id, int8_t quality)
 {
 	memset(s, 0, sizeof(ssdv_t));
 	s->image_id = image_id;
 	s->callsign = encode_callsign(callsign);
 	s->mode = S_ENCODING;
 	s->type = type;
+	s->quality = 4 + quality; /* Quality levels are -4 to 3, adjust to 0-7 */
 	ssdv_set_packet_conf(s);
 	
 	/* Prepare the output JPEG tables */
-	s->ddqt[0] = dtblcpy(s, std_dqt0, sizeof(std_dqt0));
+	s->ddqt[0] = dload_standard_dqt(s, std_dqt0, s->quality);
-	s->ddqt[1] = dtblcpy(s, std_dqt1, sizeof(std_dqt1));
+	s->ddqt[1] = dload_standard_dqt(s, std_dqt1, s->quality);
 	s->ddht[0][0] = dtblcpy(s, std_dht00, sizeof(std_dht00));
 	s->ddht[0][1] = dtblcpy(s, std_dht01, sizeof(std_dht01));
 	s->ddht[1][0] = dtblcpy(s, std_dht10, sizeof(std_dht10));
@@ -972,6 +1033,7 @@ char ssdv_enc_get_packet(ssdv_t *s)
 				s->out[9]   = s->width >> 4;       /* Width / 16 */
 				s->out[10]  = s->height >> 4;      /* Height / 16 */
 				s->out[11]  = 0x00;
+				s->out[11] |= s->quality << 3;     /* Quality level */
 				s->out[11] |= (r == SSDV_EOI ? 1 : 0) << 2; /* EOI flag (1 bit) */
 				s->out[11] |= s->mcu_mode & 0x03;  /* MCU mode (2 bits) */
 				s->out[12]  = mcu_offset;          /* Next MCU offset */
@@ -1044,8 +1106,8 @@ static void ssdv_out_headers(ssdv_t *s)
 	
 	ssdv_write_marker(s, J_SOI,    0, 0);
 	ssdv_write_marker(s, J_APP0,  14, app0);
-	ssdv_write_marker(s, J_DQT,   65, std_dqt0);  /* DQT Luminance       */
+	ssdv_write_marker(s, J_DQT,   65, s->ddqt[0]);  /* DQT Luminance       */
-	ssdv_write_marker(s, J_DQT,   65, std_dqt1);  /* DQT Chrominance     */
+	ssdv_write_marker(s, J_DQT,   65, s->ddqt[1]);  /* DQT Chrominance     */
 	
 	/* Build SOF0 header */
 	b[0]  = 8; /* Precision */
@@ -1124,16 +1186,12 @@ char ssdv_dec_init(ssdv_t *s)
 	s->mode = S_DECODING;
 	
 	/* Prepare the source JPEG tables */
-	s->sdqt[0] = stblcpy(s, std_dqt0, sizeof(std_dqt0));
-	s->sdqt[1] = stblcpy(s, std_dqt1, sizeof(std_dqt1));
 	s->sdht[0][0] = stblcpy(s, std_dht00, sizeof(std_dht00));
 	s->sdht[0][1] = stblcpy(s, std_dht01, sizeof(std_dht01));
 	s->sdht[1][0] = stblcpy(s, std_dht10, sizeof(std_dht10));
 	s->sdht[1][1] = stblcpy(s, std_dht11, sizeof(std_dht11));
 	
 	/* Prepare the output JPEG tables */
-	s->ddqt[0] = dtblcpy(s, std_dqt0, sizeof(std_dqt0));
-	s->ddqt[1] = dtblcpy(s, std_dqt1, sizeof(std_dqt1));
 	s->ddht[0][0] = dtblcpy(s, std_dht00, sizeof(std_dht00));
 	s->ddht[0][1] = dtblcpy(s, std_dht01, sizeof(std_dht01));
 	s->ddht[1][0] = dtblcpy(s, std_dht10, sizeof(std_dht10));
@@ -1182,12 +1240,19 @@ char ssdv_dec_feed(ssdv_t *s, uint8_t *packet)
 		s->width     = packet[9] << 4;
 		s->height    = packet[10] << 4;
 		s->mcu_count = packet[9] * packet[10];
+		s->quality   = (packet[11] >> 3) & 7;
 		s->mcu_mode  = packet[11] & 0x03;
 		
 		/* Configure the payload size and CRC position */
 		ssdv_set_packet_conf(s);
 		
-		switch(s->mcu_mode)
+		/* Generate the DQT tables */
+		s->sdqt[0] = sload_standard_dqt(s, std_dqt0, s->quality);
+		s->sdqt[1] = sload_standard_dqt(s, std_dqt1, s->quality);
+		s->ddqt[0] = dload_standard_dqt(s, std_dqt0, s->quality);
+		s->ddqt[1] = dload_standard_dqt(s, std_dqt1, s->quality);
+		
+		switch(s->mcu_mode & 3)
 		{
 		case 0: factor = "2x2"; s->ycparts = 4; break;
 		case 1: factor = "1x2"; s->ycparts = 2; s->mcu_count *= 2; break;
@@ -1201,6 +1266,7 @@ char ssdv_dec_feed(ssdv_t *s, uint8_t *packet)
 		fprintf(stderr, "Resolution: %ix%i\n", s->width, s->height);
 		fprintf(stderr, "MCU blocks: %i\n", s->mcu_count);
 		fprintf(stderr, "Sampling factor: %s\n", factor);
+		fprintf(stderr, "Quality level: %d\n", s->quality - 4);
 		
 		/* Output JPEG headers and enable byte stuffing */
 		ssdv_out_headers(s);
@@ -1398,6 +1464,7 @@ void ssdv_dec_header(ssdv_packet_info_t *info, uint8_t *packet)
 	info->width      = packet[9] << 4;
 	info->height     = packet[10] << 4;
 	info->eoi        = (packet[11] >> 2) & 1;
+	info->quality    = (packet[11] >> 3) & 7;
 	info->mcu_mode   = packet[11] & 0x03;
 	info->mcu_offset = packet[12];
 	info->mcu_id     = (packet[13] << 8) | packet[14];

ssdv.h

@@ -63,6 +63,7 @@ typedef struct
 	uint8_t  mcu_mode;  /* 0 = 2x2, 1 = 2x1, 2 = 1x2, 3 = 1x1           */
 	uint16_t mcu_id;
 	uint16_t mcu_count;
+	uint8_t  quality;   /* JPEG quality level for encoding, 0-7         */
 	uint16_t packet_mcu_id;
 	uint8_t  packet_mcu_offset;
 	
@@ -135,6 +136,7 @@ typedef struct {
 	uint16_t width;
 	uint16_t height;
 	uint8_t  eoi;
+	uint8_t  quality;
 	uint16_t mcu_mode;
 	uint8_t  mcu_offset;
 	uint16_t mcu_id;
@@ -142,7 +144,7 @@ typedef struct {
 } ssdv_packet_info_t;
 
 /* Encoding */
-extern char ssdv_enc_init(ssdv_t *s, uint8_t type, char *callsign, uint8_t image_id);
+extern char ssdv_enc_init(ssdv_t *s, uint8_t type, char *callsign, uint8_t image_id, int8_t quality);
 extern char ssdv_enc_set_buffer(ssdv_t *s, uint8_t *buffer);
 extern char ssdv_enc_get_packet(ssdv_t *s);
 extern char ssdv_enc_feed(ssdv_t *s, uint8_t *buffer, size_t length);