[libcamera-devel] [PATCH 4/5] ipa: ipu3: agc: Return the inter-quantile mean from measureBrightness()
Jean-Michel Hautbois
jeanmichel.hautbois at ideasonboard.com
Wed Nov 17 11:22:53 CET 2021
Hi Laurent,
Thanks for the patch !
On 16/11/2021 17:26, Laurent Pinchart wrote:
> The inter-quantile mean is a value that is computed as part of the AGC
> run. It doesn't need to be stored in a member variable. Return it from
> measureBrightness(), which makes the flow of data easier to follow.
>
> 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 | 53 ++++++++++++++++++---------------
> src/ipa/ipu3/algorithms/agc.h | 9 +++---
> 2 files changed, 33 insertions(+), 29 deletions(-)
>
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 6aab9fd5ebb5..71398fdd96a6 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -70,7 +70,7 @@ static constexpr uint32_t kNumStartupFrames = 10;
> static constexpr double kRelativeLuminanceTarget = 0.16;
>
> Agc::Agc()
> - : frameCount_(0), iqMean_(0.0), lineDuration_(0s), minShutterSpeed_(0s),
> + : frameCount_(0), lineDuration_(0s), minShutterSpeed_(0s),
> maxShutterSpeed_(0s), filteredExposure_(0s), currentExposure_(0s)
> {
> }
> @@ -108,9 +108,10 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
> * \brief Estimate the mean value of the top 2% of the histogram
> * \param[in] stats The statistics computed by the ImgU
> * \param[in] grid The grid used to store the statistics in the IPU3
> + * \return The mean value of the top 2% of the histogram
> */
> -void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
> - const ipu3_uapi_grid_config &grid)
> +double Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
> + const ipu3_uapi_grid_config &grid) const
> {
> /* Initialise the histogram array */
> uint32_t hist[knumHistogramBins] = { 0 };
> @@ -135,8 +136,8 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
> }
> }
>
> - /* Estimate the quantile mean of the top 2% of the histogram */
> - iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
> + /* Estimate the quantile mean of the top 2% of the histogram. */
> + return Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
> }
>
> /**
> @@ -174,28 +175,22 @@ void Agc::filterExposure()
> * \brief Estimate the new exposure and gain values
> * \param[inout] frameContext The shared IPA frame Context
> * \param[in] yGain The gain calculated based on the relative luminance target
> + * \param[in] iqMeanGain The gain calculated based on the relative luminance target
> */
> -void Agc::computeExposure(IPAFrameContext &frameContext, double yGain)
> +void Agc::computeExposure(IPAFrameContext &frameContext, double yGain,
> + double iqMeanGain)
> {
> /* Get the effective exposure and gain applied on the sensor. */
> uint32_t exposure = frameContext.sensor.exposure;
> double analogueGain = frameContext.sensor.gain;
>
> - /*
> - * Estimate the gain needed to have the proportion of pixels in a given
> - * desired range. iqMean_ returns the mean value of the top 2% of the
> - * cumulative histogram, and we want it to be as close as possible to a
> - * configured target.
> - */
> - double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
> -
> - if (evGain < yGain)
> - evGain = yGain;
> + /* Use the highest of the two gain estimates. */
> + double evGain = std::max(yGain, iqMeanGain);
>
> /* Consider within 1% of the target as correctly exposed */
> if (std::abs(evGain - 1.0) < 0.01)
> - LOG(IPU3Agc, Debug) << "We are well exposed (iqMean = "
> - << iqMean_ << ")";
> + LOG(IPU3Agc, Debug) << "We are well exposed (evGain = "
> + << evGain << ")";
>
> /* extracted from Rpi::Agc::computeTargetExposure */
>
> @@ -308,15 +303,25 @@ double Agc::estimateLuminance(IPAFrameContext &frameContext,
> */
> void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
> {
> - measureBrightness(stats, context.configuration.grid.bdsGrid);
> + /*
> + * Estimate the gain needed to have the proportion of pixels in a given
> + * desired range. iqMean is the mean value of the top 2% of the
> + * cumulative histogram, and we want it to be as close as possible to a
> + * configured target.
> + */
> + double iqMean = measureBrightness(stats, context.configuration.grid.bdsGrid);
> + double iqMeanGain = kEvGainTarget * knumHistogramBins / iqMean;
>
> + /*
> + * Estimate the gain needed to achieve a relative luminance target. To
> + * account for non-linearity caused by saturation, the value needs to be
> + * estimated in an iterative process, as multiplying by a gain will not
> + * increase the relative luminance by the same factor if some image
> + * regions are saturated.
> + */
> double yGain = 1.0;
> double yTarget = kRelativeLuminanceTarget;
>
> - /*
> - * Do this calculation a few times as brightness increase can be
> - * non-linear when there are saturated regions.
> - */
> for (unsigned int i = 0; i < 8; i++) {
> double yValue = estimateLuminance(context.frameContext,
> context.configuration.grid.bdsGrid,
> @@ -331,7 +336,7 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
> break;
> }
>
> - computeExposure(context.frameContext, yGain);
> + computeExposure(context.frameContext, yGain, iqMeanGain);
> frameCount_++;
> }
>
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index 0c868d6737f1..a04a81fb8eae 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -31,10 +31,11 @@ public:
> void process(IPAContext &context, const ipu3_uapi_stats_3a *stats) override;
>
> private:
> - void measureBrightness(const ipu3_uapi_stats_3a *stats,
> - const ipu3_uapi_grid_config &grid);
> + double measureBrightness(const ipu3_uapi_stats_3a *stats,
> + const ipu3_uapi_grid_config &grid) const;
> void filterExposure();
> - void computeExposure(IPAFrameContext &frameContext, double yGain);
> + void computeExposure(IPAFrameContext &frameContext, double yGain,
> + double iqMeanGain);
> double estimateLuminance(IPAFrameContext &frameContext,
> const ipu3_uapi_grid_config &grid,
> const ipu3_uapi_stats_3a *stats,
> @@ -42,8 +43,6 @@ private:
>
> uint64_t frameCount_;
>
> - double iqMean_;
> -
> utils::Duration lineDuration_;
> utils::Duration minShutterSpeed_;
> utils::Duration maxShutterSpeed_;
>
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