From fe7ff490746e82ba1c1766872f6b3ee29f84724a Mon Sep 17 00:00:00 2001
From: Philip Heron <phil@sanslogic.co.uk>
Date: Sun, 29 Jan 2012 18:56:17 +0000
Subject: [PATCH] Only reset the MCU DC values for the first MCU on each packet

---
 .gitignore |  2 +-
 ssdv.c     | 37 ++++++++++++++++++++++++++-----------
 ssdv.h     | 10 ++++++----
 3 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/.gitignore b/.gitignore
index 3318b89..57592d9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
 ssdv
 *.o
 *.jpeg
-*.bin
+*.bin*
diff --git a/ssdv.c b/ssdv.c
index fe01018..25bb505 100644
--- a/ssdv.c
+++ b/ssdv.c
@@ -314,9 +314,9 @@ static char ssdv_process(ssdv_t *s)
 			if(symbol == 0x00)
 			{
 				/* No change in DC from last block */
-				if(s->mcupart == 0 || s->mcupart == 4 || s->mcupart == 5)
+				if(s->reset_mcu == s->mcu_id && (s->mcupart == 0 || s->mcupart == 4 || s->mcupart == 5))
 				{
-					if(s->dcmode == 0) ssdv_out_jpeg_int(s, 0, AADJ(s->dc[s->component]));
+					if(s->mode == S_ENCODING) ssdv_out_jpeg_int(s, 0, s->adc[s->component]);
 					else
 					{
 						ssdv_out_jpeg_int(s, 0, 0 - s->dc[s->component]);
@@ -376,13 +376,14 @@ static char ssdv_process(ssdv_t *s)
 		
 		if(s->acpart == 0) /* DC */
 		{
-			if(s->mcupart == 0 || s->mcupart == 4 || s->mcupart == 5)
+			if(s->reset_mcu == s->mcu_id && (s->mcupart == 0 || s->mcupart == 4 || s->mcupart == 5))
 			{
-				if(s->dcmode == 0)
+				if(s->mode == S_ENCODING)
 				{
 					/* Output absolute DC value */
 					s->dc[s->component] += UADJ(i);
-					ssdv_out_jpeg_int(s, 0, AADJ(s->dc[s->component]));
+					s->adc[s->component] = AADJ(s->dc[s->component]);
+					ssdv_out_jpeg_int(s, 0, s->adc[s->component]);
 				}
 				else
 				{
@@ -393,9 +394,21 @@ static char ssdv_process(ssdv_t *s)
 			}
 			else
 			{
-				/* Output relative DC value */
-				s->dc[s->component] += UADJ(i);
-				ssdv_out_jpeg_int(s, 0, BADJ(i));
+				if(s->mode == S_DECODING)
+				{
+					s->dc[s->component] += UADJ(i);
+					ssdv_out_jpeg_int(s, 0, i);
+				}
+				else
+				{
+					/* Output relative DC value */
+					s->dc[s->component] += UADJ(i);
+					
+					/* Calculate closest adjusted DC value */
+				 	i = AADJ(s->dc[s->component]);
+					ssdv_out_jpeg_int(s, 0, i - s->adc[s->component]);
+					s->adc[s->component] = i;
+				}
 			}
 		}
 		else /* AC */
@@ -453,6 +466,7 @@ static char ssdv_process(ssdv_t *s)
 			/* Set the packet MCU marker - encoder only */
 			if(s->packet_mcu_id == 0xFFFF)
 			{
+				if(s->mode == S_ENCODING) s->reset_mcu = s->mcu_id;
 				s->packet_mcu_id = s->mcu_id;
 				s->packet_mcu_offset =
 					(SSDV_PKT_SIZE_PAYLOAD - s->out_len) * 8 + s->outlen;
@@ -677,6 +691,7 @@ char ssdv_enc_init(ssdv_t *s, uint8_t image_id)
 {
 	memset(s, 0, sizeof(ssdv_t));
 	s->image_id = image_id;
+	s->mode = S_ENCODING;
 	return(SSDV_OK);
 }
 
@@ -933,9 +948,7 @@ char ssdv_dec_init(ssdv_t *s)
 	
 	/* The packet data should contain only scan data, no headers */
 	s->state = S_HUFF;
-	
-	/* Converting absolute values to relative */
-	s->dcmode = 1;
+	s->mode = S_DECODING;
 	
 	return(SSDV_OK);
 }
@@ -965,6 +978,8 @@ char ssdv_dec_feed(ssdv_t *s, uint8_t *packet)
 	s->packet_mcu_offset = (packet[7] << 8) | packet[8];
 	s->packet_mcu_id     = (packet[9] << 8) | packet[10];
 	
+	if(s->packet_mcu_id != 0xFFFF) s->reset_mcu = s->packet_mcu_id;
+	
 	/* If this is the first packet, write the JPEG headers */
 	if(s->packet_id == 0)
 	{
diff --git a/ssdv.h b/ssdv.h
index 7216730..5d03a7a 100644
--- a/ssdv.h
+++ b/ssdv.h
@@ -89,17 +89,19 @@ typedef struct
 	uint8_t mcupart;    /* 0-3 = Y, 4 = Cb, 5 = Cr                      */
 	uint8_t acpart;     /* 0 - 64; 0 = DC, 1 - 64 = AC                  */
 	int dc[COMPONENTS]; /* DC value for each component                  */
+	int adc[COMPONENTS];/* DC adjusted value for each component         */
 	uint8_t acrle;      /* RLE value for current AC value               */
 	uint8_t accrle;     /* Accumulative RLE value                       */
-	char dcmode;        /* 0 = Absolute, 1 = Relative (parts 0, 4 & 5)  */
+	enum {
+		S_ENCODING = 0,
+		S_DECODING,
+	} mode;
+	uint32_t reset_mcu; /* MCU block to do absolute encoding            */
 	char needbits;      /* Number of bits needed to decode integer      */
 	
 	/* Small buffer for reading SOF0 and SOS header data into */
 	uint8_t hbuff[HBUFF_LEN];
 	
-	/* SSDV2 experiment */
-	int block[64];
-	
 } ssdv_t;
 
 typedef struct {