[libcamera-devel] [PATCH v11 1/3] libcamera: controls: Add frame duration control

[Laurent Pinchart]

Hi Naush,

On Tue, Jan 12, 2021 at 07:17:14AM +0000, Naushir Patuck wrote:
> On Mon, 11 Jan 2021 at 23:07, Laurent Pinchart wrote:
> > On Wed, Jan 06, 2021 at 10:06:57AM +0000, Naushir Patuck wrote:
> > > Add an int64_t array control (controls::FrameDurations) to specify the
> > > minimum and maximum (in that order) frame duration to be used by the
> > > camera sensor.
> > >
> > > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > > Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> > > Tested-by: David Plowman <david.plowman at raspberrypi.com>
> > > Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
> > > ---
> > >  src/libcamera/control_ids.yaml | 38 ++++++++++++++++++++++++++++++++++
> > >  1 file changed, 38 insertions(+)
> > >
> > > diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > index 6d6f0fee..d1240beb 100644
> > > --- a/src/libcamera/control_ids.yaml
> > > +++ b/src/libcamera/control_ids.yaml
> > > @@ -306,6 +306,44 @@ controls:
> > >          maximum valid value is given by the properties::ScalerCropMaximum
> > >          property, and the two can be used to implement digital zoom.
> > >
> > > +  - FrameDurations:
> > > +      type: int64_t
> > > +      description: |
> > > +          The minimum and maximum (in that order) frame duration,
> > > +          expressed in micro-seconds.
> >
> > s/micro-seconds/microseconds/
> >
> > (The indentation should be 2 spaces btw)
> >
> > > +
> > > +          When provided by applications, the control specifies the sensor frame
> > > +          duration interval the pipeline has to use. This limits the largest
> > > +          exposure time the sensor can use. For example, if a maximum frame
> > > +          duration of 33ms is requested (corresponding to 30 frames per second),
> > > +          the sensor will not be able to raise the exposure time above 33ms.
> > > +          A fixed frame duration is achieved by setting the minimum and maximum
> > > +          values to be the same. Setting both values to 0 reverts to using the
> > > +          IPA provided defaults.
> > > +
> > > +          The maximum frame duration provides the absolute limit to the shutter
> > > +          speed computed by the AE algorithm and it overrides any exposure mode
> > > +          setting specified with controls::AeExposureMode. Similarly, when a
> > > +          manual exposure time is set through controls::ExposureTime, it also
> > > +          gets clipped to the limits set by this control.
> >
> > This looks good.
> >
> > >            When reported in
> > > +          metadata, the control expresses the minimum and maximum frame
> > > +          durations used after being clipped to these limits.
> > > +
> >
> > But this sounds weird. The previous part states that FrameDurations has
> > higher priority than all other parameters, but then this sentence says
> > it's clipped by "these limits".
> 
> You are right, this does not read correct.  I wanted to express that the
> frame durations provided may be further limited by what the sensor mode can
> actually achieve.  How about replacing the above paragraph of text with the
> following:
> 
> When reported in metadata, the control expresses the minimum and maximum
> frame durations used after being clipped to the sensor provided frame
> duration limits.

Sounds good to me.

> > > +          \sa AeExposureMode
> > > +          \sa ExposureTime
> > > +
> > > +          \todo Refer to the frame duration limits property to describe how
> > > +          application-provided values gets clipped and reset.
> >
> > It hasn't been long, and the context is already starting to escape me.
> > Would it be possible to expand this just a little bit so that we'll know
> > what it means in 3 months time ?
> 
> Perhaps this makes more sense given the rewording above?  Or maybe a reword
> as follows:
> 
> \todo Refer to the frame duration limits property to describe how
> application-provided values get clipped to what is supported by the sensor
> mode.
> 
> Hopefully that makes things more readable?

Not quite I'm afraid, but maybe it's just too early in the morning :-)

Is this about documenting how other properties also get clipped by the
sensor mode ? Or something else ?

> > > +
> > > +          \todo Define how to calculate the capture frame rate by
> > > +          defining controls to report additional delays introduced by
> > > +          the capture pipeline or post-processing stages (ie JPEG
> > > +          conversion, frame scaling).
> > > +
> > > +          \todo Provide an explicit definition of default control values, for
> > > +          this and all other controls.
> > > +      size: [2]
> > > +
> > >    # ----------------------------------------------------------------------------
> > >    # Draft controls section
> > >

-- 
Regards,

Laurent Pinchart