[libcamera-devel] [PATCH v4 31/32] ipa: rkisp1: awb: Freeze AWB when means are too small

[Jacopo Mondi]

Hi Laurent

On Thu, Sep 08, 2022 at 04:41:59AM +0300, Laurent Pinchart via libcamera-devel wrote:
> When the RGB means are too small, gains and color temperature can't be
> meaningfully calculated. Freeze the AWB in that case, using the
> previously calculated values.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/ipa/rkisp1/algorithms/awb.cpp | 17 ++++++++++++++++-
>  src/ipa/rkisp1/ipa_context.cpp    |  3 +++
>  src/ipa/rkisp1/ipa_context.h      |  1 +
>  3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/src/ipa/rkisp1/algorithms/awb.cpp b/src/ipa/rkisp1/algorithms/awb.cpp
> index 5f2535688c93..404ad66e6953 100644
> --- a/src/ipa/rkisp1/algorithms/awb.cpp
> +++ b/src/ipa/rkisp1/algorithms/awb.cpp
> @@ -31,6 +31,9 @@ namespace ipa::rkisp1::algorithms {
>
>  LOG_DEFINE_CATEGORY(RkISP1Awb)
>
> +/* Minimum mean value below which AWB can't operate. */
> +constexpr double kMeanMinThreshold = 2.0;
> +

Is this a software constraint specified somewhere ?

>  Awb::Awb()
>  	: rgbMode_(false)
>  {
> @@ -263,7 +266,17 @@ void Awb::process(IPAContext &context,
>  	greenMean /= frameContext.awb.gains.green;
>  	blueMean /= frameContext.awb.gains.blue;
>
> -	frameContext.awb.temperatureK = estimateCCT(redMean, greenMean, blueMean);
> +	/*
> +	 * If the means are too small we don't have enough information to
> +	 * meaningfully calculate gains. Freeze the algorithm in that case.
> +	 */
> +	if (redMean < kMeanMinThreshold && greenMean < kMeanMinThreshold &&
> +	    blueMean < kMeanMinThreshold) {
> +		frameContext.awb.temperatureK = activeState.awb.temperatureK;
> +		return;
> +	}
> +
> +	activeState.awb.temperatureK = estimateCCT(redMean, greenMean, blueMean);
>
>  	/*
>  	 * Estimate the red and blue gains to apply in a grey world. The green
> @@ -290,6 +303,8 @@ void Awb::process(IPAContext &context,
>  	activeState.awb.gains.automatic.blue = blueGain;
>  	activeState.awb.gains.automatic.green = 1.0;
>
> +	frameContext.awb.temperatureK = activeState.awb.temperatureK;
> +
>  	LOG(RkISP1Awb, Debug) << std::showpoint
>  		<< "Means [" << redMean << ", " << greenMean << ", " << blueMean
>  		<< "], gains [" << activeState.awb.gains.automatic.red << ", "
> diff --git a/src/ipa/rkisp1/ipa_context.cpp b/src/ipa/rkisp1/ipa_context.cpp
> index 335cb32c538d..9cac05bec79b 100644
> --- a/src/ipa/rkisp1/ipa_context.cpp
> +++ b/src/ipa/rkisp1/ipa_context.cpp
> @@ -156,6 +156,9 @@ namespace libcamera::ipa::rkisp1 {
>   * \var IPAActiveState::awb.gains.automatic.blue
>   * \brief Automatic white balance gain for B channel
>   *
> + * \var IPAActiveState::awb.temperatureK
> + * \brief Estimated color temperature
> + *
>   * \var IPAActiveState::awb.autoEnabled
>   * \brief Whether the Auto White Balance algorithm is enabled
>   */
> diff --git a/src/ipa/rkisp1/ipa_context.h b/src/ipa/rkisp1/ipa_context.h
> index 53787320e565..d0bc9090a8f1 100644
> --- a/src/ipa/rkisp1/ipa_context.h
> +++ b/src/ipa/rkisp1/ipa_context.h
> @@ -68,6 +68,7 @@ struct IPAActiveState {
>  			} automatic;
>  		} gains;
>
> +		unsigned int temperatureK;
>  		bool autoEnabled;
>  	} awb;
>
> --
> Regards,
>
> Laurent Pinchart
>