From 06779c6bdda8274f1f67e82b95c5504653690623 Mon Sep 17 00:00:00 2001
From: Přemysl Eric Janouch <p@janouch.name>
Date: Fri, 3 Dec 2021 14:56:55 +0100
Subject: jpeginfo: decode basic TIFF tag names

---
 tools/jpeginfo.c | 129 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 127 insertions(+), 2 deletions(-)

diff --git a/tools/jpeginfo.c b/tools/jpeginfo.c
index 0a5f2ae..4545746 100644
--- a/tools/jpeginfo.c
+++ b/tools/jpeginfo.c
@@ -324,6 +324,120 @@ tiffer_next_entry(struct tiffer *self, struct tiffer_entry *entry)
 	return true;
 }
 
+// --- TIFF/Exif/MPF/* tags ----------------------------------------------------
+
+struct tiff_entry {
+	const char *name;
+	uint16_t tag;
+};
+
+static struct tiff_entry tiff_entries[] = {
+	{"NewSubfileType", 254},
+	{"SubfileType", 255},
+	{"ImageWidth", 256},
+	{"ImageLength", 257},
+	{"BitsPerSample", 258},
+	{"Compression", 259},
+	{"PhotometricInterpretation", 262},
+	{"Threshholding", 263},
+	{"CellWidth", 264},
+	{"CellLength", 265},
+	{"FillOrder", 266},
+	{"DocumentName", 269},
+	{"ImageDescription", 270},
+	{"Make", 271},
+	{"Model", 272},
+	{"StripOffsets", 273},
+	{"Orientation", 274},
+	{"SamplesPerPixel", 277},
+	{"RowsPerStrip", 278},
+	{"StripByteCounts", 279},
+	{"MinSampleValue", 280},
+	{"MaxSampleValue", 281},
+	{"XResolution", 282},
+	{"YResolution", 283},
+	{"PlanarConfiguration", 284},
+	{"PageName", 285},
+	{"XPosition", 286},
+	{"YPosition", 287},
+	{"FreeOffsets", 288},
+	{"FreeByteCounts", 289},
+	{"GrayResponseUnit", 290},
+	{"GrayResponseCurve", 291},
+	{"T4Options", 292},
+	{"T6Options", 293},
+	{"ResolutionUnit", 296},
+	{"PageNumber", 297},
+	{"TransferFunction", 301},
+	{"Software", 305},
+	{"DateTime", 306},
+	{"Artist", 315},
+	{"HostComputer", 316},
+	{"Predictor", 317},
+	{"WhitePoint", 318},
+	{"PrimaryChromaticities", 319},
+	{"ColorMap", 320},
+	{"HalftoneHints", 321},
+	{"TileWidth", 322},
+	{"TileLength", 323},
+	{"TileOffsets", 324},
+	{"TileByteCounts", 325},
+	{"InkSet", 332},
+	{"InkNames", 333},
+	{"NumberOfInks", 334},
+	{"DotRange", 336},
+	{"TargetPrinter", 337},
+	{"ExtraSamples", 338},
+	{"SampleFormat", 339},
+	{"SMinSampleValue", 340},
+	{"SMaxSampleValue", 341},
+	{"TransferRange", 342},
+	{"JPEGProc", 512},
+	{"JPEGInterchangeFormat", 513},
+	{"JPEGInterchangeFormatLngth", 514},
+	{"JPEGRestartInterval", 515},
+	{"JPEGLosslessPredictors", 517},
+	{"JPEGPointTransforms", 518},
+	{"JPEGQTables", 519},
+	{"JPEGDCTables", 520},
+	{"JPEGACTables", 521},
+	{"YCbCrCoefficients", 529},
+	{"YCbCrSubSampling", 530},
+	{"YCbCrPositioning", 531},
+	{"ReferenceBlackWhite", 532},
+	{"Copyright", 33432},
+	{}
+};
+
+// Compression
+static struct tiff_entry tiff_compression_values[] = {
+	{"Uncompressed", 1},
+	{"CCITT 1D", 2},
+	{"Group 3 Fax", 3},
+	{"Group 4 Fax", 4},
+	{"LZW", 5},
+	{"JPEG", 6},
+	{"PackBits", 32773},
+	{}
+};
+
+// PhotometricInterpretation
+static struct tiff_entry tiff_photometric_interpretation_values[] = {
+	{"WhiteIsZero", 0},
+	{"BlackIsZero", 1},
+	{"RGB", 2},
+	{"RGB Palette", 3},
+	{"Transparency mask", 4},
+	{"CMYK", 5},
+	{"YCbCr", 6},
+	{"CIELab", 8},
+	{}
+};
+
+// TODO(p): Insert tags and values from other documentation,
+// so far only Appendix A from TIFF 6.0 is present.
+// There are still quite a few missing constant names from there.
+
 // --- Analysis ----------------------------------------------------------------
 
 static jv
@@ -351,6 +465,17 @@ add_error(jv o, const char *message)
 
 // --- Exif --------------------------------------------------------------------
 
+// TODO(p): Decode more and better.
+static jv
+process_exif_entry(jv o, const struct tiffer_entry *entry)
+{
+	for (const struct tiff_entry *p = tiff_entries; p->name; p++) {
+		if (p->tag == entry->tag)
+			return add_to_subarray(o, "TIFF", jv_string(p->name));
+	}
+	return add_to_subarray(o, "TIFF", jv_number(entry->tag));
+}
+
 static jv
 parse_exif(jv o, const uint8_t *p, size_t len)
 {
@@ -358,11 +483,11 @@ parse_exif(jv o, const uint8_t *p, size_t len)
 	if (!tiffer_init(&T, p, len))
 		return add_warning(o, "invalid Exif");
 
-	// TODO(p): Decode more and better.
+	// TODO(p): Turn this into an array of objects indexed by tag name.
 	struct tiffer_entry entry;
 	while (tiffer_next_ifd(&T)) {
 		while (tiffer_next_entry(&T, &entry)) {
-			o = add_to_subarray(o, "TIFF", jv_number(entry.tag));
+			o = process_exif_entry(o, &entry);
 		}
 	}
 	return o;
-- 
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