[PATCH v3 2/2] ipa: rpi: awb: Add a bias to the AWB search

[Laurent Pinchart]

On Tue, Oct 08, 2024 at 09:13:17AM +0100, Naushir Patuck wrote:
> In the case of an AWB search failure, the current algorithm logic will
> return a point on the CT curve closest to where the search finisned.
> This can be quite undesirable. Instead, add some bias params to the AWB
> algorithm which will direct the search to a set CT value in the case
> where statistics become unreliable causing the search to fail.
> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  src/ipa/rpi/controller/rpi/awb.cpp | 23 +++++++++++++++++++++--
>  src/ipa/rpi/controller/rpi/awb.h   |  4 ++++
>  2 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/src/ipa/rpi/controller/rpi/awb.cpp b/src/ipa/rpi/controller/rpi/awb.cpp
> index 65416d05b28e..9d8e170d1bfe 100644
> --- a/src/ipa/rpi/controller/rpi/awb.cpp
> +++ b/src/ipa/rpi/controller/rpi/awb.cpp
> @@ -170,6 +170,14 @@ int AwbConfig::read(const libcamera::YamlObject &params)
>  	whitepointB = params["whitepoint_b"].get<double>(0.0);
>  	if (bayes == false)
>  		sensitivityR = sensitivityB = 1.0; /* nor do sensitivities make any sense */
> +	/*
> +	 * The biasProportion parameter adds a small proportion of the counted
> +	 * pixles to a region biased to the biasCT colour temperature.

s/pixles/pixels/

> +	 *
> +	 * A typical value for biasProportion would be between 0.05 to 0.1.
> +	 */
> +	biasProportion = params["bias_proportion"].get<double>(0.0);
> +	biasCT = params["bias_ct"].get<double>(kDefaultCT);
>  	return 0;
>  }
>  
> @@ -410,7 +418,8 @@ void Awb::asyncFunc()
>  
>  static void generateStats(std::vector<Awb::RGB> &zones,
>  			  StatisticsPtr &stats, double minPixels,
> -			  double minG, Metadata &globalMetadata)
> +			  double minG, Metadata &globalMetadata,
> +			  double biasProportion, double biasCtR, double biasCtB)
>  {
>  	std::scoped_lock<RPiController::Metadata> l(globalMetadata);
>  
> @@ -423,6 +432,14 @@ static void generateStats(std::vector<Awb::RGB> &zones,
>  				continue;
>  			zone.R = region.val.rSum / region.counted;
>  			zone.B = region.val.bSum / region.counted;
> +			/*
> +			 * Add some bias samples to allow the search to tend to a
> +			 * bias CT in failure cases.
> +			 */
> +			const unsigned int proportion = biasProportion * region.counted;
> +			zone.R += proportion * biasCtR;
> +			zone.B += proportion * biasCtB;
> +			zone.G += proportion * 1.0;
>  			/* Factor in the ALSC applied colour shading correction if required. */
>  			const AlscStatus *alscStatus = globalMetadata.getLocked<AlscStatus>("alsc.status");
>  			if (stats->colourStatsPos == Statistics::ColourStatsPos::PreLsc && alscStatus) {
> @@ -443,7 +460,9 @@ void Awb::prepareStats()
>  	 * any LSC compensation.  We also ignore config_.fast in this version.
>  	 */
>  	generateStats(zones_, statistics_, config_.minPixels,
> -		      config_.minG, getGlobalMetadata());
> +		      config_.minG, getGlobalMetadata(),
> +		      config_.biasProportion, config_.ctR.eval(config_.biasCT),
> +		      config_.ctB.eval(config_.biasCT));
>  	/*
>  	 * apply sensitivities, so values appear to come from our "canonical"
>  	 * sensor.
> diff --git a/src/ipa/rpi/controller/rpi/awb.h b/src/ipa/rpi/controller/rpi/awb.h
> index ab30f4fa51c1..5d628b47c8a6 100644
> --- a/src/ipa/rpi/controller/rpi/awb.h
> +++ b/src/ipa/rpi/controller/rpi/awb.h
> @@ -87,6 +87,10 @@ struct AwbConfig {
>  	double whitepointR;
>  	double whitepointB;
>  	bool bayes; /* use Bayesian algorithm */
> +	/* proportion of counted samples to add for the search bias */
> +	double biasProportion;
> +	/* CT target for the search bias */
> +	double biasCT;
>  };
>  
>  class Awb : public AwbAlgorithm

-- 
Regards,

Laurent Pinchart