[libcamera-devel] [PATCH 4/5] src: ipa: raspberrypi: Move initial frame drop decision to AGC

[Laurent Pinchart]

Hi Naush and David,

On Fri, Dec 04, 2020 at 04:01:42PM +0000, Naushir Patuck wrote:
> On Wed, 2 Dec 2020 at 11:53, David Plowman wrote:
> 
> > Previously the CamHelper was returning the number of frames to drop
> > (on account of AGC converging). This wasn't really appropriate, it's
> > better for the AGC to do it, which now also knows when exposure and
> > gain have been explicitly set and therefore fewer (or no) frame drops
> > are necessary at all.
> >
> > The CamHelper::HideFramesStartup method should now just be returning
> > the number of frames to hide because they're bad/invalid in some way,
> > not worrying about the AGC. For many sensors, the correct value for
> > this is zero.
> >
> > Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> > ---
> >  src/ipa/raspberrypi/cam_helper.cpp  | 6 +++---
> >  src/ipa/raspberrypi/raspberrypi.cpp | 8 ++++++++
> >  2 files changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/ipa/raspberrypi/cam_helper.cpp
> > b/src/ipa/raspberrypi/cam_helper.cpp
> > index c8ac3232..6efa0d7f 100644
> > --- a/src/ipa/raspberrypi/cam_helper.cpp
> > +++ b/src/ipa/raspberrypi/cam_helper.cpp
> > @@ -82,10 +82,10 @@ bool CamHelper::SensorEmbeddedDataPresent() const
> >  unsigned int CamHelper::HideFramesStartup() const
> >  {
> >         /*
> > -        * By default, hide 6 frames completely at start-up while AGC etc. sort
> > -        * themselves out (converge).
> > +        * The number of frames when a camera first starts that shouldn't be
> > +        * displayed as they are invalid in some way.
> >          */
> > -       return 6;
> > +       return 0;
> >  }
> >
> >  unsigned int CamHelper::HideFramesModeSwitch() const
> > diff --git a/src/ipa/raspberrypi/raspberrypi.cpp
> > b/src/ipa/raspberrypi/raspberrypi.cpp
> > index 0300b8d9..ddabdb31 100644
> > --- a/src/ipa/raspberrypi/raspberrypi.cpp
> > +++ b/src/ipa/raspberrypi/raspberrypi.cpp
> > @@ -192,6 +192,14 @@ int IPARPi::start(const IPAOperationData &ipaConfig,
> > IPAOperationData *result)
> >         unsigned int dropFrame = 0;
> >         if (firstStart_) {
> >                 dropFrame = helper_->HideFramesStartup();
> > +
> > +               /* The AGC algorithm may want us to drop more frames. */
> > +               RPiController::AgcAlgorithm *agc = dynamic_cast<RPiController::AgcAlgorithm *>(
> > +                       controller_.GetAlgorithm("agc"));
> > +               if (agc)
> > +                       dropFrame = std::max(dropFrame, agc->GetDropFrames());
> > +               LOG(IPARPI, Debug) << "Drop " << dropFrame << " frames on startup";
> > +
> 
> All looks good with this change, however, I have a possibly silly
> question.  In the previous code, our startup frames would account for
> convergence in AGC, AWB, and ALS.  Here we are explicitly accounting for
> convergence only in AGC since helper_->HideFramesStartup()  will return 0
> by default.  Does it matter? Should each derived CamHelper return a
> non-zero number here?

Unless I'm mistaken, HideFramesStartup() is meant to report how many
incorrectly exposed (and "gained") frames are produced by the sensor at
startup, even if exposure time and gain are programmed before starting
the sensor. This will certainly impact AWB and ALS as they will have
trouble operating if the frame is greatly underexposed, but the sensor
is otherwise not involved in AWB and ALS. I thus don't think CamHelper
should take AWB and ALS into account.

With this new split of responsibilities, with CamHelper reporting the
number of frames that are bad (for different reasons, underexposed,
incorrect metadata, ...) and the algorithms then deciding how long they
need before initially converging, Shouldn't agc->GetDropFrames() be
given the HideFramesStartup() value as a parameter, and return a new
number, instead of taking the maximum between the two ?

I also wonder if we then need the hide/mistrust split anymore,
especially with the comment in CamHelperOv5647::MistrustFramesStartup()
that mentions underexposed frames. Is there still a difference between
the two concepts ?

Finally, do we actually need to report a number of frames to drop at
startup to the pipeline handler, can't we rely on the algorithms status
reported through AeLocked and AwbLocked ? Maybe we should report only
the number of frames that are definitely bad based on the CamHelper, and
use algorithm status to report initial convergence of the algorithms ?

> >                 mistrustCount_ = helper_->MistrustFramesStartup();
> >         } else {
> >                 dropFrame = helper_->HideFramesModeSwitch();

-- 
Regards,

Laurent Pinchart