From: sgunderson@bigfoot.com <>
Date: Sat, 30 May 2009 23:50:46 +0000 (+0200)
Subject: Add DQT parsing.
X-Git-Url: https://git.sesse.net/?p=fjl;a=commitdiff_plain;h=4f5e260fc1163b9383c565035e73f30bedbeec92

Add DQT parsing.
---

diff --git a/driver.c b/driver.c
index dd1b1ae..bbc569e 100644
--- a/driver.c
+++ b/driver.c
@@ -12,6 +12,7 @@ struct jpeg_image {
 	unsigned width, height;
 	unsigned num_components;
 	unsigned hsample[256], vsample[256], qtable[256];
+	uint32_t qvalues[256][DCTSIZE2];
 };
 
 ssize_t stdio_read(void* userdata, uint8_t* buf, size_t count) 
@@ -19,6 +20,33 @@ ssize_t stdio_read(void* userdata, uint8_t* buf, size_t count)
 	return fread(buf, 1, count, (FILE*)userdata);
 }
 
+void read_dqt(struct byte_source* source, struct jpeg_image* image)
+{
+	unsigned len = read_uint16(byte_source_input_func, source);
+	assert(len >= 67);
+	uint8_t precision_table = read_uint8(byte_source_input_func, source);
+	int precision = precision_table >> 4;  // 0 = 8 bits, otherwise 16 bits.
+	int table = precision_table & 0x0f;
+
+	if (precision != 0) {
+		assert(len == 131);
+		fprintf(stderr, "Quantization table %u: 16 bits/entry\n", table);
+	} else {
+		assert(len == 67);
+		fprintf(stderr, "Quantization table %u: 8 bits/entry\n", table);
+	}
+	
+	for (unsigned i = 0; i < 64; ++i) {
+		if (precision != 0) {
+			image->qvalues[table][unzigzag[i]] =
+				read_uint16(byte_source_input_func, source);
+		} else {
+			image->qvalues[table][unzigzag[i]] =
+				read_uint8(byte_source_input_func, source);
+		}	
+	}
+}
+
 void read_sof(struct byte_source* source, struct jpeg_image* image)
 {
 	unsigned len = read_uint16(byte_source_input_func, source);
@@ -193,9 +221,11 @@ int main(void)
 			/* comment */
 		case 0xff:
 			/* ignore */
+			skip_segment(&source);
+			break;
 		case 0xdb:
 			/* DQT */
-			skip_segment(&source);
+			read_dqt(&source, &jpeg);
 			break;
 		case 0xc0:
 			/* SOF0 (baseline DCT, Huffman encoded) */