[libcamera-devel] [PATCH] qcam: dng_writer: Write EXIF IFD as custom directory

[Kieran Bingham]

Hi Laurent,

On 04/05/2020 08:04, Laurent Pinchart wrote:
> The EXIF IFD is incorrectly chained to IFD 0 in addition to being a
> referenced as a sub IFD through the EXIFIFD tag. While the libtiff API
> doesn't clearly document why this happens, inspection of the
> TIFFWriteDirectory() source code show that the function treats the IFD
> being written as containing an image, which isn't correct for the EXIF
> IFD. Use TIFFWriteCustomDirectory() instead, which fixes the problem.
> The resulting DNG file can now be opened with darktable in addition to
> rawtherapee.

Nice!

Sounds like it was more painful to fix than it should have been.

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/qcam/dng_writer.cpp | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/src/qcam/dng_writer.cpp b/src/qcam/dng_writer.cpp
> index ea4616f63d8e..cbd8bed3e6d0 100644
> --- a/src/qcam/dng_writer.cpp
> +++ b/src/qcam/dng_writer.cpp
> @@ -316,9 +316,7 @@ int DNGWriter::write(const char *filename, const Camera *camera,
>  		TIFFSetField(tif, EXIFTAG_EXPOSURETIME, exposureTime);
>  	}
>  
> -	TIFFCheckpointDirectory(tif);
> -	exifIFDOffset = TIFFCurrentDirOffset(tif);
> -	TIFFWriteDirectory(tif);
> +	TIFFWriteCustomDirectory(tif, &exifIFDOffset);
>  
>  	/* Update the IFD offsets and close the file. */
>  	TIFFSetDirectory(tif, 0);
> 

-- 
Regards
--
Kieran