From 6bad5339881ad37957edfffce29300cf93a495af Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Thu, 17 Jul 2008 15:53:35 +0000
Subject: [PATCH] better jpeg-in-tiff YCbCr read

---
 ChangeLog                        |  1 +
 TODO                             |  2 +
 libsrc/conversion/im_tiff2vips.c | 63 +++++++-------------------------
 3 files changed, 17 insertions(+), 49 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 0ae65f2e..279c3fa4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -32,6 +32,7 @@
 - now tests for MagickWand before ImageMagick (thanks Adam) 
 - added "-rotate" option to vips2dj
 - added man page for im_resize_linear
+- better jpeg-in-tiff YCbCr read (thanks Ole)
 
 25/1/08 started 7.14.0
 - bump all version numbers for new stable
diff --git a/TODO b/TODO
index 0e7d19c8..1358729f 100644
--- a/TODO
+++ b/TODO
@@ -1,5 +1,7 @@
 - wrap meta() stuff in C++, we need it in py as well
 
+- TIFF JPEG read needs to map ycbcr->rgb somehow
+
 - try
 
 	libsrc/convolution$ grep -l offsets *.c
diff --git a/libsrc/conversion/im_tiff2vips.c b/libsrc/conversion/im_tiff2vips.c
index 6d5211e2..213e11c7 100644
--- a/libsrc/conversion/im_tiff2vips.c
+++ b/libsrc/conversion/im_tiff2vips.c
@@ -101,6 +101,8 @@
  * 	- set IM_META_RESOLUTION_UNIT
  * 17/4/08
  * 	- allow CMYKA (thanks Doron)
+ * 17/7/08
+ * 	- convert YCbCr to RGB on read
  */
 
 /*
@@ -401,45 +403,6 @@ parse_labs( ReadTiff *rtiff, IMAGE *out )
 	return( 0 );
 }
 
-/* Per-scanline process function for IM_CODING_LABQ.
- */
-static void
-ycbcr_line( PEL *q, PEL *p, int n, void *dummy )
-{
-	int x;
-
-	for( x = 0; x < n; x++ ) {
-		q[0] = p[0];
-		q[1] = p[1];
-		q[2] = p[2];
-		q[3] = 0;
-
-		q += 4;
-		p += 3;
-	}
-}
-
-/* Read a YCbCr image.
- */
-static int
-parse_ycbcr( ReadTiff *rtiff, IMAGE *out )
-{
-	if( !tfequals( rtiff->tiff, TIFFTAG_SAMPLESPERPIXEL, 3 ) ||
-		!tfequals( rtiff->tiff, TIFFTAG_BITSPERSAMPLE, 8 ) )
-		return( -1 );
-
-	out->Bands = 4; 
-	out->Bbits = 8; 
-	out->BandFmt = IM_BANDFMT_UCHAR; 
-	out->Coding = IM_CODING_LABQ; 
-	out->Type = IM_TYPE_LAB; 
-
-	rtiff->sfn = ycbcr_line;
-	rtiff->client = NULL;
-
-	return( 0 );
-}
-
 /* Per-scanline process function for 1 bit images.
  */
 static void
@@ -707,7 +670,7 @@ parse_palette( ReadTiff *rtiff, IMAGE *out )
 	return( 0 );
 }
 
-/* Per-scanline process function for 8-bit RGB/RGBA/CMYK/CMYKA.
+/* Per-scanline process function for 8-bit RGB/RGBA/CMYK/CMYKA/etc.
  */
 static void
 rgbcmyk8_line( PEL *q, PEL *p, int n, IMAGE *im )
@@ -1014,14 +977,6 @@ parse_header( ReadTiff *rtiff, IMAGE *out )
 
 		break;
 
-	case PHOTOMETRIC_YCBCR:
-		/* Easy decision!
-		 */
-		if( parse_ycbcr( rtiff, out ) )
-			return( -1 );
-
-		break;
-
 	case PHOTOMETRIC_MINISWHITE:
 	case PHOTOMETRIC_MINISBLACK:
 		switch( bps ) {
@@ -1078,8 +1033,18 @@ parse_header( ReadTiff *rtiff, IMAGE *out )
 
 		break;
 
+	case PHOTOMETRIC_YCBCR:
+		/* Sometimes JPEG in TIFF images are tagged as YCBCR. Ask
+		 * libtiff to convert to RGB for us.
+		 */
+		TIFFSetField( rtiff->tiff, 
+			TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
+		if( parse_rgb8( rtiff, out ) )
+			return( -1 );
+		break;
+
 	case PHOTOMETRIC_RGB:
-		/* Plain RGB.
+		/* RGB.
 		 */
 		switch( bps ) {
 		case 8: