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

[Kieran Bingham]

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 ...

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
>