[libcamera-devel] [PATCH 5/5] qcam: dng_writer: Generate thumbnail in RGB format

[Laurent Pinchart]

While the DNG specification supports greyscale ("BlackIsZero") for
thumbnails, RawTherapee seems to have trouble reading them. Generate
thumbnails in RGB instead (but still with greyscale content, to avoid
having to interpolate colour components).

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/qcam/dng_writer.cpp | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/qcam/dng_writer.cpp b/src/qcam/dng_writer.cpp
index d04a8e161218..bc1a63e69799 100644
--- a/src/qcam/dng_writer.cpp
+++ b/src/qcam/dng_writer.cpp
@@ -74,7 +74,10 @@ void thumbScanlineSBGGRxxP(const FormatInfo &info, void *output,
 	unsigned int skip = info.bitsPerSample * 16 / 8;
 
 	for (unsigned int x = 0; x < width; x++) {
-		*out++ = (in[0] + in[1] + in[stride] + in[stride + 1]) >> 2;
+		uint8_t value = (in[0] + in[1] + in[stride] + in[stride + 1]) >> 2;
+		*out++ = value;
+		*out++ = value;
+		*out++ = value;
 		in += skip;
 	}
 }
@@ -175,16 +178,17 @@ int DNGWriter::write(const char *filename, const Camera *camera,
 	TIFFSetField(tif, TIFFTAG_ORIENTATION, ORIENTATION_TOPLEFT);
 
 	/*
-	 * Thumbnail-specific tags. The thumbnail is stored as a greyscale image
-	 * with 1/16 of the raw image resolution.
+	 * Thumbnail-specific tags. The thumbnail is stored as an RGB image
+	 * with 1/16 of the raw image resolution. Greyscale would save space,
+	 * but doesn't seem well supported by RawTherapee.
 	 */
 	TIFFSetField(tif, TIFFTAG_SUBFILETYPE, FILETYPE_REDUCEDIMAGE);
 	TIFFSetField(tif, TIFFTAG_IMAGEWIDTH, config.size.width / 16);
 	TIFFSetField(tif, TIFFTAG_IMAGELENGTH, config.size.height / 16);
 	TIFFSetField(tif, TIFFTAG_BITSPERSAMPLE, 8);
 	TIFFSetField(tif, TIFFTAG_COMPRESSION, COMPRESSION_NONE);
-	TIFFSetField(tif, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_MINISBLACK);
-	TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 1);
+	TIFFSetField(tif, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_RGB);
+	TIFFSetField(tif, TIFFTAG_SAMPLESPERPIXEL, 3);
 	TIFFSetField(tif, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);
 	TIFFSetField(tif, TIFFTAG_SAMPLEFORMAT, SAMPLEFORMAT_UINT);
 
-- 
Regards,

Laurent Pinchart