[libcamera-devel] [PATCH 06/13] ipa: ipu3: agc: Change exposure limits

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-10-13 16:41:18)
> The exposure limits are set for one sensor until now, in a number of
> lines. We should not use those, but exposure limits in a time unit.
> 
> Introduce default limits which with a default minimum of 20ms. This
> value should be given by the IPAIPU3. Use cached values expressed as a
> number of lines in the configure() call.
> 
> Adapt the process() call accordingly.

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 30 +++++++++++++++++-------------
>  src/ipa/ipu3/algorithms/agc.h   |  3 ++-
>  2 files changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 7c2d4201..2dd5c5c1 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -40,8 +40,8 @@ static constexpr uint32_t kMinGain = kMinISO / 100;
>  static constexpr uint32_t kMaxGain = kMaxISO / 100;
>  
>  /* \todo use calculated value based on sensor */
> -static constexpr uint32_t kMinExposure = 1;
> -static constexpr uint32_t kMaxExposure = 1976;
> +static constexpr libcamera::utils::Duration kMinShutterSpeed = 100us;
> +static constexpr libcamera::utils::Duration kMaxShutterSpeed = 20ms;

I guess these limits impose restrictions on long exposure support somehow?
But we don't need to worry about that for now.

>  
>  /* Histogram constants */
>  static constexpr uint32_t knumHistogramBins = 256;
> @@ -49,8 +49,8 @@ static constexpr double kEvGainTarget = 0.5;
>  
>  Agc::Agc()
>         : frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
> -         maxExposureTime_(0s), filteredExposure_(0s), filteredExposureNoDg_(0s),
> -         currentExposure_(0s), currentExposureNoDg_(0s)
> +         minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
> +         filteredExposureNoDg_(0s), currentExposure_(0s), currentExposureNoDg_(0s)
>  {
>  }
>  
> @@ -60,7 +60,9 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
>  
>         lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
>                       / configInfo.sensorInfo.pixelRate;
> -       maxExposureTime_ = kMaxExposure * lineDuration_;
> +
> +       minExposureLines_ = kMinShutterSpeed / lineDuration_;
> +       maxExposureLines_ = kMaxShutterSpeed / lineDuration_;
>  
>         return 0;
>  }
> @@ -140,28 +142,30 @@ void Agc::lockExposureGain(uint32_t &exposure, double &gain)
>                 double newGain = kEvGainTarget * knumHistogramBins / iqMean_;
>  
>                 /* extracted from Rpi::Agc::computeTargetExposure */
> -               libcamera::utils::Duration currentShutter = exposure * lineDuration_;
> +               Duration currentShutter = exposure * lineDuration_;
>                 currentExposureNoDg_ = currentShutter * gain;
>                 LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
>                                     << " Shutter speed " << currentShutter
>                                     << " Gain " << gain;
> +
>                 currentExposure_ = currentExposureNoDg_ * newGain;
> -               libcamera::utils::Duration maxTotalExposure = maxExposureTime_ * kMaxGain;
> +               Duration maxTotalExposure = kMaxShutterSpeed * kMaxGain;
>                 currentExposure_ = std::min(currentExposure_, maxTotalExposure);
> -               LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_;
> +               LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
> +                                   << " maximum is " << maxTotalExposure;
>  
>                 /* \todo: estimate if we need to desaturate */
>                 filterExposure();
>  
> -               libcamera::utils::Duration newExposure = 0.0s;
> -               if (currentShutter < maxExposureTime_) {
> -                       exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / currentExposureNoDg_), kMinExposure, kMaxExposure);
> +               Duration newExposure = 0.0s;
> +               if (currentShutter < kMaxShutterSpeed) {
> +                       exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / currentExposureNoDg_), minExposureLines_, maxExposureLines_);
>                         newExposure = currentExposure_ / exposure;
>                         gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / newExposure), kMinGain, kMaxGain);
> -               } else if (currentShutter >= maxExposureTime_) {
> +               } else if (currentShutter >= kMaxShutterSpeed) {
>                         gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / currentExposureNoDg_), kMinGain, kMaxGain);
>                         newExposure = currentExposure_ / gain;
> -                       exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / newExposure), kMinExposure, kMaxExposure);
> +                       exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / newExposure), minExposureLines_, maxExposureLines_);
>                 }
>                 LOG(IPU3Agc, Debug) << "Adjust exposure " << exposure * lineDuration_ << " and gain " << gain;
>         }
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index cd4d4855..7605ab39 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -44,7 +44,8 @@ private:
>         double iqMean_;
>  
>         Duration lineDuration_;
> -       Duration maxExposureTime_;
> +       uint32_t minExposureLines_;
> +       uint32_t maxExposureLines_;
>  
>         Duration filteredExposure_;
>         Duration filteredExposureNoDg_;
> -- 
> 2.30.2
>