[libcamera-devel] [PATCH v2 13/13] ipa: ipu3: Use sensor limits for analogue gain

[Laurent Pinchart]

Hi Jean-Michel,

Thank you for the patch.

On Wed, Oct 20, 2021 at 05:46:07PM +0200, Jean-Michel Hautbois wrote:
> Instead of using constants for the analogue gains limits, use the
> minimum and maximum from the configured sensor.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 25 +++++++++++++------------
>  src/ipa/ipu3/algorithms/agc.h   |  3 +++
>  2 files changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index fc37eca4..690ad7e6 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -30,10 +30,9 @@ static constexpr uint32_t kInitialFrameMinAECount = 4;
>  /* Number of frames to wait between new gain/exposure estimations */
>  static constexpr uint32_t kFrameSkipCount = 6;
>  
> -/* Maximum analogue gain value
> - * \todo grab it from a camera helper */
> -static constexpr double kMinGain = 1.0;
> -static constexpr double kMaxGain = 8.0;
> +/* Limits for analogue gain values */
> +static constexpr double kMinAnalogueGain = 1.0;
> +static constexpr double kMaxAnalogueGain = 16.0;

Should we keep 8.0, or is there a reason to allow gains up to 16.0 ? It
seems like it will add lots of noise.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  
>  /* Histogram constants */
>  static constexpr uint32_t knumHistogramBins = 256;
> @@ -53,15 +52,17 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
>  	lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
>  		      / configInfo.sensorInfo.pixelRate;
>  
> -	/* Configure the default exposure and gain */
> -	context.frameContext.agc.gain =
> -		context.configuration.agc.minAnalogueGain;
> -	context.frameContext.agc.exposure = minExposureLines_;
> -
>  	/* \todo replace the exposure in lines storage with time based ones */
>  	minExposureLines_ = context.configuration.agc.minShutterSpeed / lineDuration_;
>  	maxExposureLines_ = context.configuration.agc.maxShutterSpeed / lineDuration_;
>  
> +	minAnalogueGain_ = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
> +	maxAnalogueGain_ = std::min(context.configuration.agc.maxAnalogueGain, kMaxAnalogueGain);
> +
> +	/* Configure the default exposure and gain */
> +	context.frameContext.agc.gain = minAnalogueGain_;
> +	context.frameContext.agc.exposure = minExposureLines_;
> +
>  	prevExposureValue_ = context.frameContext.agc.gain
>  			   * context.frameContext.agc.exposure
>  			   * lineDuration_;
> @@ -139,7 +140,7 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
>  	utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
>  	utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
>  
> -	utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
> +	utils::Duration maxTotalExposure = maxShutterSpeed * maxAnalogueGain_;
>  	currentExposure_ = std::min(currentExposure_, maxTotalExposure);
>  	LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
>  			    << ", maximum is " << maxTotalExposure;
> @@ -154,10 +155,10 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
>  	* Push the shutter time up to the maximum first, and only then
>  	* increase the gain.
>  	*/
> -	shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
> +	shutterTime = std::clamp<utils::Duration>(exposureValue / minAnalogueGain_,
>  						  minShutterSpeed, maxShutterSpeed);
>  	double stepGain = std::clamp(exposureValue / shutterTime,
> -				     kMinGain, kMaxGain);
> +				     minAnalogueGain_, maxAnalogueGain_);
>  	LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
>  			    << shutterTime << " and "
>  			    << stepGain;
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index ad133b98..1840205b 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -45,6 +45,9 @@ private:
>  	uint32_t minExposureLines_;
>  	uint32_t maxExposureLines_;
>  
> +	double minAnalogueGain_;
> +	double maxAnalogueGain_;
> +
>  	utils::Duration filteredExposure_;
>  	utils::Duration currentExposure_;
>  	utils::Duration prevExposureValue_;

-- 
Regards,

Laurent Pinchart