[libcamera-devel] [PATCH v2 3/5] ipa: ipu3: agc: Rename currentYGain

[Jean-Michel Hautbois]

Hi Laurent,

On 19/11/2021 22:02, Laurent Pinchart wrote:
> The "current" prefix in the currentYGain variable name is confusing:
> 
> - In Agc::estimateLuminance(), the variable contains the gain to be
>    applied to the image, which is neither a "current" gain nor a "Y"
>    gain. Rename it to "gain".
> 
> - In Agc::computeExposure(), the variable contains the gain computed by
>    the relative luminance method, so rename it to "yGain".
> 
> While at it, rename variables to match the libcamera coding style.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>   src/ipa/ipu3/algorithms/agc.cpp | 32 ++++++++++++++++----------------
>   src/ipa/ipu3/algorithms/agc.h   |  4 ++--
>   2 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 9cd2ded501ed..2d196fd63c7e 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -173,9 +173,9 @@ void Agc::filterExposure()
>   /**
>    * \brief Estimate the new exposure and gain values
>    * \param[inout] frameContext The shared IPA frame Context
> - * \param[in] currentYGain The gain calculated on the current brightness level
> + * \param[in] yGain The gain calculated based on the relative luminance target
>    */
> -void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
> +void Agc::computeExposure(IPAFrameContext &frameContext, double yGain)
>   {
>   	/* Get the effective exposure and gain applied on the sensor. */
>   	uint32_t exposure = frameContext.sensor.exposure;
> @@ -189,8 +189,8 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
>   	 */
>   	double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
>   
> -	if (evGain < currentYGain)
> -		evGain = currentYGain;
> +	if (evGain < yGain)
> +		evGain = yGain;
>   
>   	/* Consider within 1% of the target as correctly exposed */
>   	if (std::abs(evGain - 1.0) < 0.01)
> @@ -254,7 +254,7 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
>    * \param[in] frameContext The shared IPA frame context
>    * \param[in] grid The grid used to store the statistics in the IPU3
>    * \param[in] stats The IPU3 statistics and ISP results
> - * \param[in] currentYGain The gain calculated on the current brightness level
> + * \param[in] gain The gain to apply to the frame
>    * \return The relative luminance
>    *
>    * Luma is the weighted sum of gamma-compressed R′G′B′ components of a color
> @@ -268,7 +268,7 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
>   double Agc::estimateLuminance(IPAFrameContext &frameContext,
>   			      const ipu3_uapi_grid_config &grid,
>   			      const ipu3_uapi_stats_3a *stats,
> -			      double currentYGain)
> +			      double gain)
>   {
>   	double redSum = 0, greenSum = 0, blueSum = 0;
>   
> @@ -281,9 +281,9 @@ double Agc::estimateLuminance(IPAFrameContext &frameContext,
>   					&stats->awb_raw_buffer.meta_data[cellPosition]
>   				);
>   
> -			redSum += cell->R_avg * currentYGain;
> -			greenSum += (cell->Gr_avg + cell->Gb_avg) / 2 * currentYGain;
> -			blueSum += cell->B_avg * currentYGain;
> +			redSum += cell->R_avg * gain;
> +			greenSum += (cell->Gr_avg + cell->Gb_avg) / 2 * gain;
> +			blueSum += cell->B_avg * gain;
>   		}
>   	}
>   
> @@ -310,7 +310,7 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
>   {
>   	measureBrightness(stats, context.configuration.grid.bdsGrid);
>   
> -	double currentYGain = 1.0;
> +	double yGain = 1.0;
>   	double yTarget = kRelativeLuminanceTarget;
>   
>   	/*
> @@ -320,18 +320,18 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
>   	for (unsigned int i = 0; i < 8; i++) {
>   		double yValue = estimateLuminance(context.frameContext,
>   						  context.configuration.grid.bdsGrid,
> -						  stats, currentYGain);
> -		double extra_gain = std::min(10.0, yTarget / (yValue + .001));
> +						  stats, yGain);
> +		double extraGain = std::min(10.0, yTarget / (yValue + .001));
>   
> -		currentYGain *= extra_gain;
> +		yGain *= extraGain;
>   		LOG(IPU3Agc, Debug) << "Y value: " << yValue
>   				    << ", Y target: " << yTarget
> -				    << ", gives gain " << currentYGain;
> -		if (extra_gain < 1.01)
> +				    << ", gives gain " << yGain;
> +		if (extraGain < 1.01)
>   			break;
>   	}
>   
> -	computeExposure(context.frameContext, currentYGain);
> +	computeExposure(context.frameContext, yGain);
>   	frameCount_++;
>   }
>   
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index 943c354a820e..0c868d6737f1 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -34,11 +34,11 @@ private:
>   	void measureBrightness(const ipu3_uapi_stats_3a *stats,
>   			       const ipu3_uapi_grid_config &grid);
>   	void filterExposure();
> -	void computeExposure(IPAFrameContext &frameContext, double currentYGain);
> +	void computeExposure(IPAFrameContext &frameContext, double yGain);
>   	double estimateLuminance(IPAFrameContext &frameContext,
>   				 const ipu3_uapi_grid_config &grid,
>   				 const ipu3_uapi_stats_3a *stats,
> -				 double currentYGain);
> +				 double gain);
>   
>   	uint64_t frameCount_;
>   
>