[2/3] ipa: simple: agc: Read limits from tuning

27776 diff mbox series

The simple IPA AGC currently uses one target and the full exposure and gain
ranges reported by the sensor. On the tested ov08x40 setup that produced more
noise and longer exposures than were useful for a webcam.

Allow tuning to set the histogram target, maximum analogue gain and maximum
exposure time. Missing values preserve the current behaviour, and configured
limits are clamped to the sensor's reported range.

Build-tested against libcamera base b8910c9a4961 and hardware-tested as part of
the complete patch set on the target HP Spectre.

Signed-off-by: James Alexander <opensource@inspiredexperts.com>
---

Hi James,

On Sun, Aug 16, 2026 at 02:42:58PM -0600, James Alexander wrote:
> The simple IPA AGC currently uses one target and the full exposure and gain
> ranges reported by the sensor. On the tested ov08x40 setup that produced more
> noise and longer exposures than were useful for a webcam.
>
> Allow tuning to set the histogram target, maximum analogue gain and maximum
> exposure time. Missing values preserve the current behaviour, and configured
> limits are clamped to the sensor's reported range.
>
> Build-tested against libcamera base b8910c9a4961 and hardware-tested as part of
> the complete patch set on the target HP Spectre.
>

Barnabas, Stefan: once Simple will be ported to AgcMeanLuminance, are
there tuning parameters for the algorithm that allow to restrict the
search space to obain something similar to what James' doing here with
custom properties ?

Thanks
  j



> Signed-off-by: James Alexander <opensource@inspiredexperts.com>
> ---
> diff --git a/src/ipa/simple/algorithms/agc.cpp b/src/ipa/simple/algorithms/agc.cpp
> index a13a755..fa93d03 100644
> --- a/src/ipa/simple/algorithms/agc.cpp
> +++ b/src/ipa/simple/algorithms/agc.cpp
> @@ -8,6 +8,7 @@
>  #include "agc.h"
>
>  #include <algorithm>
> +#include <chrono>
>  #include <cmath>
>  #include <stdint.h>
>
> @@ -15,6 +16,8 @@
>
>  #include "control_ids.h"
>
> +using namespace std::literals::chrono_literals;
> +
>  namespace libcamera {
>
>  LOG_DEFINE_CATEGORY(IPASoftExposure)
> @@ -62,7 +65,46 @@ static constexpr float kExpProportionalGain = 0.04;
>  static constexpr float kExpMaxStep = 0.15;
>
>  Agc::Agc()
> +	: exposureOptimal_(kExposureOptimal)
> +{
> +}
> +
> +int Agc::init([[maybe_unused]] IPAContext &context, const ValueNode &tuningData)
> +{
> +	auto target = tuningData["target"].get<double>();
> +	if (target.has_value())
> +		exposureOptimal_ = std::clamp(target.value(), 1.0, 5.0);
> +
> +	auto maxAnalogueGain = tuningData["maxAnalogueGain"].get<double>();
> +	if (maxAnalogueGain.has_value())
> +		maxAnalogueGain_ = std::max(1.0, maxAnalogueGain.value());
> +
> +	auto maxExposureTimeMs = tuningData["maxExposureTimeMs"].get<double>();
> +	if (maxExposureTimeMs.has_value())
> +		maxExposureTimeMs_ = std::max(1.0, maxExposureTimeMs.value());
> +
> +	return 0;
> +}
> +
> +int Agc::configure(IPAContext &context,
> +		   [[maybe_unused]] const IPAConfigInfo &configInfo)
>  {
> +	if (maxAnalogueGain_.has_value())
> +		context.configuration.agc.againMax =
> +			std::clamp(maxAnalogueGain_.value(),
> +				   context.configuration.agc.againMin,
> +				   context.configuration.agc.againMax);
> +
> +	if (maxExposureTimeMs_.has_value()) {
> +		utils::Duration maxExposure = maxExposureTimeMs_.value() * 1.0ms;
> +		int32_t maxExposureLines =
> +			std::max<int32_t>(context.configuration.agc.exposureMin,
> +					  maxExposure / context.configuration.agc.lineDuration);
> +		context.configuration.agc.exposureMax =
> +			std::min(context.configuration.agc.exposureMax, maxExposureLines);
> +	}
> +
> +	return 0;
>  }
>
>  void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, double exposureMSV)
> @@ -70,7 +112,7 @@ void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, dou
>  	int32_t &exposure = frameContext.sensor.exposure;
>  	double &again = frameContext.sensor.gain;
>
> -	double error = kExposureOptimal - exposureMSV;
> +	double error = exposureOptimal_ - exposureMSV;
>
>  	if (std::abs(error) <= kExposureSatisfactory)
>  		return;
> diff --git a/src/ipa/simple/algorithms/agc.h b/src/ipa/simple/algorithms/agc.h
> index 112d9f5..501252f 100644
> --- a/src/ipa/simple/algorithms/agc.h
> +++ b/src/ipa/simple/algorithms/agc.h
> @@ -7,6 +7,8 @@
>
>  #pragma once
>
> +#include <optional>
> +
>  #include "algorithm.h"
>
>  namespace libcamera {
> @@ -19,6 +21,9 @@ public:
>  	Agc();
>  	~Agc() = default;
>
> +	int init(IPAContext &context, const ValueNode &tuningData) override;
> +	int configure(IPAContext &context,
> +		      const IPAConfigInfo &configInfo) override;
>  	void process(IPAContext &context, const uint32_t frame,
>  		     IPAFrameContext &frameContext,
>  		     const SwIspStats *stats,
> @@ -26,6 +31,10 @@ public:
>
>  private:
>  	void updateExposure(IPAContext &context, IPAFrameContext &frameContext, double exposureMSV);
> +
> +	double exposureOptimal_;
> +	std::optional<double> maxAnalogueGain_;
> +	std::optional<double> maxExposureTimeMs_;
>  };
>
>  } /* namespace ipa::soft::algorithms */
> --
> 2.46.0