[libcamera-devel] [PATCH 3/3] src: ipa: raspberrypi: Fix initial AGC oscillation for imx219 sensor

[Laurent Pinchart]

Hi Naush,

On Thu, Nov 26, 2020 at 10:37:47AM +0000, Naushir Patuck wrote:
> On Thu, 26 Nov 2020 at 10:20, Laurent Pinchart wrote:
> > On Wed, Nov 25, 2020 at 11:36:40AM +0000, David Plowman wrote:
> > > The exposure times in the exposure modes were causing AGC oscillations
> > > because the algorithm was demanding long unachievable exposure times
> > > but, without working sensor metadata, thought it was getting them when
> > > actually it was not. We fix it by making the exposure profile request
> > > only achievable exposure times, as we do for the ov5647 tuning.
> >
> > This looks good to me, and I assume it will still work with sensor
> > embedded data, as unachievable exposure times are, well, unachievable
> > :-)
> >
> > Is the process to select shutter values documented in the RPi camera
> > documentation, or the tuning tool ? If someone wants to bring up a new
> > sensor, how can we ensure a similar bug will not creep in ?
> 
> My work on FPS control does fix this problem in a generic way for
> non-embedded data sensors. This is done by ensuring we only send exposure
> values that will be validated based on vblank limits, thereby ensuring the
> return path (without embedded data) will be given the same values used by
> the sensor device. For embedded data sensors, it all "just works", hence
> our preference to use it where available ;-)

Wouldn't algorithms still be able to do a better job when splitting
sensitivity control between exposure time and gain if they know
beforehand what exposure times are achievable, instead of waiting for
the embedded data to report the actual value later ? My concern here is
that I don't see any reason why it would be desirable to specify
unachievable shutter times in the tuning parameters, so we should try to
avoid it, especially if it can degrade performances. Making sure we
document this properly would be a good first step.

> > > Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >
> > > ---
> > >  src/ipa/raspberrypi/data/imx219.json | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/src/ipa/raspberrypi/data/imx219.json b/src/ipa/raspberrypi/data/imx219.json
> > > index b03a7beb..212f8b9a 100644
> > > --- a/src/ipa/raspberrypi/data/imx219.json
> > > +++ b/src/ipa/raspberrypi/data/imx219.json
> > > @@ -133,7 +133,7 @@
> > >              {
> > >                  "shutter":
> > >                  [
> > > -                    100, 10000, 30000, 60000, 120000
> > > +                    100, 10000, 30000, 30000, 30000
> > >                  ],
> > >                  "gain":
> > >                  [
> > > @@ -144,7 +144,7 @@
> > >              {
> > >                  "shutter":
> > >                  [
> > > -                    100, 5000, 10000, 20000, 120000
> > > +                    100, 5000, 10000, 20000, 30000
> > >                  ],
> > >                  "gain":
> > >                  [

-- 
Regards,

Laurent Pinchart