[{"id":38855,"web_url":"https://patchwork.libcamera.org/comment/38855/","msgid":"<85h5oetdvs.fsf@mzamazal-thinkpadp1gen7.tpbc.csb>","date":"2026-05-11T10:54:47","subject":"Re: [PATCH v2 08/10] ipa: simple: agc: Read exposure target and\n\tgain from YAML","submitter":{"id":177,"url":"https://patchwork.libcamera.org/api/people/177/","name":"Milan Zamazal","email":"mzamazal@redhat.com"},"content":"d3vv3 writes:\n\n> Replace the hardcoded kExposureOptimal, kExposureSatisfactory, and\n> kExpProportionalGain constants with member variables read from the\n> tuning file as exposureTarget, hysteresis, and proportionalGain.\n> Defaults match the previous values (2.5, 0.2, 0.04).\n>\n> The constants are renamed to match their YAML keys and to use standard\n> control-theory terminology:\n>\n> - kExposureOptimal -> exposureTarget: \"optimal\" implies a single\n> universally correct value; \"target\" is the conventional ISP/AGC term\n> for the setpoint the controller drives towards and is sensor-dependent.\n>\n> - kExposureSatisfactory -> hysteresis: the old name described the effect\n> (exposure is satisfactory within this band) rather than the mechanism.\n> \"hysteresis\" is the standard term for a deadband that prevents\n> oscillation around a setpoint.\n>\n> - kExpProportionalGain -> proportionalGain: drops the redundant kExp\n> prefix and matches the YAML key name directly.\n>\n> Signed-off-by: d3vv3 \n\nReviewed-by: Milan Zamazal \n\n> ---\n> src/ipa/simple/algorithms/agc.cpp | 33 ++++++++++++++++++++-----------\n> src/ipa/simple/algorithms/agc.h | 8 ++++++++\n> 2 files changed, 30 insertions(+), 11 deletions(-)\n>\n> diff --git a/src/ipa/simple/algorithms/agc.cpp b/src/ipa/simple/algorithms/agc.cpp\n> index ac977d5f..66618d0f 100644\n> --- a/src/ipa/simple/algorithms/agc.cpp\n> +++ b/src/ipa/simple/algorithms/agc.cpp\n> @@ -28,45 +28,56 @@ static constexpr unsigned int kExposureBinsCount = 5;\n> \n> /*\n> * The exposure is optimal when the mean sample value of the histogram is\n> - * in the middle of the range.\n> + * in the middle of the range. Overridable via YAML exposureTarget.\n> */\n> -static constexpr float kExposureOptimal = kExposureBinsCount / 2.0;\n> +static constexpr float kExposureTargetDefault = kExposureBinsCount / 2.0;\n> \n> /*\n> * This implements the hysteresis for the exposure adjustment.\n> * It is small enough to have the exposure close to the optimal, and is big\n> * enough to prevent the exposure from wobbling around the optimal value.\n> */\n> -static constexpr float kExposureSatisfactory = 0.2;\n> +static constexpr float kHysteresisDefault = 0.2;\n> \n> /*\n> * Proportional gain for exposure/gain adjustment. Maps the MSV error to a\n> * multiplicative correction factor:\n> *\n> - * factor = 1.0 + kExpProportionalGain * error\n> + * factor = 1.0 + proportionalGain_ * error\n> *\n> - * With kExpProportionalGain = 0.04:\n> + * With proportionalGain_ = 0.04:\n> * - max error ~2.5 -> factor 1.10 (~10% step, same as before)\n> * - error 1.0 -> factor 1.04 (~4% step)\n> * - error 0.3 -> factor 1.012 (~1.2% step)\n> *\n> - * This replaces the fixed 10% bang-bang step with a proportional correction\n> - * that converges smoothly and avoids overshooting near the target.\n> + * Overridable via YAML proportionalGain.\n> */\n> -static constexpr float kExpProportionalGain = 0.04;\n> +static constexpr float kProportionalGainDefault = 0.04;\n> \n> Agc::Agc()\n> {\n> }\n> \n> +int Agc::init([[maybe_unused]] IPAContext &context, const ValueNode &tuningData)\n> +{\n> +\texposureTarget_ = tuningData[\"exposureTarget\"].get()\n> +\t\t.value_or(kExposureTargetDefault);\n> +\thysteresis_ = tuningData[\"hysteresis\"].get()\n> +\t\t.value_or(kHysteresisDefault);\n> +\tproportionalGain_ = tuningData[\"proportionalGain\"].get()\n> +\t\t.value_or(kProportionalGainDefault);\n> +\n> +\treturn 0;\n> +}\n> +\n> void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, double exposureMSV)\n> {\n> \tint32_t &exposure = frameContext.sensor.exposure;\n> \tdouble &again = frameContext.sensor.gain;\n> \n> -\tdouble error = kExposureOptimal - exposureMSV;\n> +\tdouble error = exposureTarget_ - exposureMSV;\n> \n> -\tif (std::abs(error) <= kExposureSatisfactory)\n> +\tif (std::abs(error) <= hysteresis_)\n> \t\treturn;\n> \n> \t/*\n> @@ -74,7 +85,7 @@ void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, dou\n> \t * determines the direction: positive error means too dark (increase),\n> \t * negative means too bright (decrease).\n> \t */\n> -\tfloat factor = 1.0f + static_cast(error) * kExpProportionalGain;\n> +\tfloat factor = 1.0f + static_cast(error) * proportionalGain_;\n> \n> \tif (factor > 1.0f) {\n> \t\t/* Scene too dark: increase exposure first, then gain. */\n> diff --git a/src/ipa/simple/algorithms/agc.h b/src/ipa/simple/algorithms/agc.h\n> index 112d9f5a..b8ed542b 100644\n> --- a/src/ipa/simple/algorithms/agc.h\n> +++ b/src/ipa/simple/algorithms/agc.h\n> @@ -7,6 +7,8 @@\n> \n> #pragma once\n> \n> +#include \n> +\n> #include \"algorithm.h\"\n> \n> namespace libcamera {\n> @@ -19,6 +21,8 @@ public:\n> \tAgc();\n> \t~Agc() = default;\n> \n> +\tint init(IPAContext &context, const ValueNode &tuningData) override;\n> +\n> \tvoid process(IPAContext &context, const uint32_t frame,\n> \t\t IPAFrameContext &frameContext,\n> \t\t const SwIspStats *stats,\n> @@ -26,6 +30,10 @@ public:\n> \n> private:\n> \tvoid updateExposure(IPAContext &context, IPAFrameContext &frameContext, double exposureMSV);\n> +\n> +\tfloat exposureTarget_;\n> +\tfloat hysteresis_;\n> +\tfloat proportionalGain_;\n> };\n> \n> } /* namespace ipa::soft::algorithms */","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id CC253BDB1C\n\tfor ;\n\tMon, 11 May 2026 10:54:55 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 13C9863025;\n\tMon, 11 May 2026 12:54:55 +0200 (CEST)","from us-smtp-delivery-124.mimecast.com\n\t(us-smtp-delivery-124.mimecast.com [170.10.133.124])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id C586D62DC4\n\tfor ;\n\tMon, 11 May 2026 12:54:53 +0200 (CEST)","from mail-ej1-f71.google.com (mail-ej1-f71.google.com\n\t[209.85.218.71]) by relay.mimecast.com with ESMTP with STARTTLS\n\t(version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id\n\tus-mta-54-cEIri4ToPqujWPqVjaoD6g-1; Mon, 11 May 2026 06:54:51 -0400","by mail-ej1-f71.google.com with SMTP id\n\ta640c23a62f3a-bcd4170426eso178454166b.1\n\tfor ;\n\tMon, 11 May 2026 03:54:51 -0700 (PDT)","from mzamazal-thinkpadp1gen7.tpbc.csb\n\t(ip-77-48-47-4.net.vodafone.cz. 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