[libcamera-devel] [PATCH v2 05/14] ipa: ipu3: agc: Compute the gain for each frame

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-11-10 22:12:50)
> Hi Kieran,
> 
> On 10/11/2021 23:02, Kieran Bingham wrote:
> > Quoting Jean-Michel Hautbois (2021-11-10 19:58:52)
> >> Now that we have the real exposure applied at each frame, remove the
> >> early return based on a frame counter and compute the gain for each
> >> frame.
> >>
> >> Instead of that, introduce a number of startup frames during which the
> >> filter speed is 1.0, meaning we apply instantly the exposure value
> >> calculated and not a slower filtered one.
> >>
> >> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> >> ---
> >>   src/ipa/ipu3/algorithms/agc.cpp | 26 +++++++++++---------------
> >>   1 file changed, 11 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> >> index 2bf68e04..133f5931 100644
> >> --- a/src/ipa/ipu3/algorithms/agc.cpp
> >> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> >> @@ -45,11 +45,6 @@ namespace ipa::ipu3::algorithms {
> >>   
> >>   LOG_DEFINE_CATEGORY(IPU3Agc)
> >>   
> >> -/* Number of frames to wait before calculating stats on minimum exposure */
> >> -static constexpr uint32_t kInitialFrameMinAECount = 4;
> >> -/* Number of frames to wait between new gain/shutter time estimations */
> >> -static constexpr uint32_t kFrameSkipCount = 6;
> >> -
> >>   /* Limits for analogue gain values */
> >>   static constexpr double kMinAnalogueGain = 1.0;
> >>   static constexpr double kMaxAnalogueGain = 8.0;
> >> @@ -69,10 +64,13 @@ static constexpr double kEvGainTarget = 0.5;
> >>    */
> >>   static constexpr uint32_t kMinCellsPerZoneRatio = 255 * 20 / 100;
> >>   
> >> +/* Number of frames to wait before calculating stats on minimum exposure */
> >> +static constexpr uint32_t kNumStartupFrames = 10;
> >> +
> >>   Agc::Agc()
> >> -       : frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
> >> -         minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
> >> -         currentExposure_(0s), prevExposureValue_(0s)
> >> +       : frameCount_(0), iqMean_(0.0), lineDuration_(0s), minExposureLines_(0),
> > 
> > I see frameCount_ is initialised to zero here...
> > 
> > 
> >> +         maxExposureLines_(0), filteredExposure_(0s), currentExposure_(0s),
> >> +         prevExposureValue_(0s)
> >>   {
> >>   }
> >>   
> >> @@ -159,6 +157,11 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
> >>   void Agc::filterExposure()
> >>   {
> >>          double speed = 0.2;
> >> +
> >> +       /* Adapt instantly if we are in startup phase */
> >> +       if (frameCount_ < kNumStartupFrames)
> >> +               speed = 1.0;
> > 
> > And it's used to determine how long into startup we are.
> > 
> > Is it ever set to 0 on start/stop/configure operations that would
> > necessitate re-evaluating the whole startup procedure like this?
> > 
> > I can't see anything resetting it - and we don't destroy and reconstruct
> > the objects so it isn't going to be re-initialised.
> > 
> > This may be a distinctly separate (and pre-existing) bug, and likely
> > warrant a patch or fix of its own.
> > 
> > I wonder if we should instead be passing in the frame/sequence count for
> > all algorithm operations.  That (should?) be reset to zero when
> > starting/stopping I think ...
> > 
> 
> We could add the frameId in the frameContext, and fill it in 
> EventStatReady. That would solve the issue and remove the frameCount_ at 
> the same time ?


Ah yes, I think you had something like that already? Anyway, it can be
solved on top of this series. I thought we'd have shrunk the /22 down a
bit more ;-) but seems there's still plenty of change in play.

--
Kieran



> 
> > Even with that limitation, I'm tempted to say this should still go in
> > and the count can be fixed on top. I think this is still an improvement.
> > 
> > Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > 
> >> +
> >>          if (filteredExposure_ == 0s) {
> >>                  /* DG stands for digital gain.*/
> >>                  filteredExposure_ = currentExposure_;
> >> @@ -186,13 +189,6 @@ void Agc::filterExposure()
> >>    */
> >>   void Agc::computeExposure(uint32_t &exposure, double &analogueGain)
> >>   {
> >> -       /* Algorithm initialization should wait for first valid frames */
> >> -       /* \todo - have a number of frames given by DelayedControls ?
> >> -        * - implement a function for IIR */
> >> -       if ((frameCount_ < kInitialFrameMinAECount) || (frameCount_ - lastFrame_ < kFrameSkipCount))
> >> -               return;
> >> -
> >> -       lastFrame_ = frameCount_;
> >>   
> >>          /* Are we correctly exposed ? */
> >>          if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1) {
> >> -- 
> >> 2.32.0
> >>