[libcamera-devel] [PATCH] qcam: dng_writer: Record creation time in the EXIF directory

[Niklas Söderlund]

Hi Laurent,

Thanks for your feedback.

On 2020-06-11 05:47:52 +0300, Laurent Pinchart wrote:
> Hi Niklas,
> 
> Thank you for the patch.
> 
> On Thu, Jun 11, 2020 at 03:46:14AM +0200, Niklas Söderlund wrote:
> > If the EXIF directory is empty due to no metadata being available tools
> > such as tiffinfo complains that the directory is malformed.
> > 
> >     TIFFFetchDirectory: Sanity check on directory count failed, this is probably not a valid IFD offset.
> >     TIFFReadCustomDirectory: Failed to read custom directory at offset 0.
> > 
> > Always record the creation time in the EXIF directory instead of adding
> > complexity to skip creating the EXIF directory if there is no metadata
> > to record. This ensures there are at least one entry in the EXIF
> > directory and that makes tiffinfo happy.
> > 
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  src/qcam/dng_writer.cpp | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/src/qcam/dng_writer.cpp b/src/qcam/dng_writer.cpp
> > index 330b169af25b7ac7..c1c3833740d96630 100644
> > --- a/src/qcam/dng_writer.cpp
> > +++ b/src/qcam/dng_writer.cpp
> > @@ -426,6 +426,17 @@ int DNGWriter::write(const char *filename, const Camera *camera,
> >  	/* Create a new IFD for the EXIF data and fill it. */
> >  	TIFFCreateEXIFDirectory(tif);
> >  
> > +	/* Store creation time. */
> > +	time_t rawtime;
> > +	struct tm *timeinfo;
> > +	char strTime[20];
> > +
> > +	time(&rawtime);
> 
> Could we use the timestamp from the buffer instead ?

We can't as the timestamp in the buffer is copied from the v4l2 buffer 
and not guaranteed to be an offset from the epoch.

> 
> > +	timeinfo = localtime(&rawtime);
> > +	strftime(strTime, 20, "%Y:%m:%d %H:%M:%S", timeinfo);
> 
> How are time zones supposed to be handled ?

The documentation states noting about timezones so I think the best 
option is the use the local timezone of the device running qcam.

> 
> > +
> > +	TIFFSetField(tif, EXIFTAG_DATETIMEDIGITIZED, strTime);
> 
> Should we also set EXIFTAG_DATETIMEORIGINAL to the same value ?

We should will send a v2.

> 
> > +
> >  	if (metadata.contains(controls::AnalogueGain)) {
> >  		float gain = metadata.get(controls::AnalogueGain);
> >  		uint16_t iso = std::min(std::max(gain * 100, 0.0f), 65535.0f);
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Regards,
Niklas Söderlund