From patchwork Wed May 6 21:46:01 2026 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Javier Tia X-Patchwork-Id: 26648 Return-Path: X-Original-To: parsemail@patchwork.libcamera.org Delivered-To: parsemail@patchwork.libcamera.org Received: from lancelot.ideasonboard.com (lancelot.ideasonboard.com [92.243.16.209]) by patchwork.libcamera.org (Postfix) with ESMTPS id C7069C32F6 for ; Wed, 6 May 2026 22:19:46 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id 1EF266302E; Thu, 7 May 2026 00:19:46 +0200 (CEST) Authentication-Results: lancelot.ideasonboard.com; dkim=pass (2048-bit key; unprotected) header.d=jetm.me header.i=@jetm.me header.b="CmGqEsCA"; dkim=pass (2048-bit key; unprotected) header.d=messagingengine.com header.i=@messagingengine.com header.b="R98w9VOA"; dkim-atps=neutral Received: from fhigh-a6-smtp.messagingengine.com (fhigh-a6-smtp.messagingengine.com [103.168.172.157]) by lancelot.ideasonboard.com (Postfix) with ESMTPS id 310876301A for ; Thu, 7 May 2026 00:19:43 +0200 (CEST) Received: from phl-compute-02.internal (phl-compute-02.internal [10.202.2.42]) by mailfhigh.phl.internal (Postfix) with ESMTP id 74A5714000FF; Wed, 6 May 2026 18:19:42 -0400 (EDT) Received: from phl-imap-07 ([10.202.2.97]) by phl-compute-02.internal (MEProxy); Wed, 06 May 2026 18:19:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=jetm.me; h=cc:cc :content-transfer-encoding:content-type:content-type:date:date :from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to; s=fm2; t=1778105982; x=1778192382; bh=+uCojCTKCMOFVIV59W7fSxyYCD3fDWoJOIKPEBSOamQ=; b= CmGqEsCAEW/7L4YCkQ99iPcFk2FUmHP1qcFrYZjDf2ps7enCm1Zl21wvqlqlHPFn 8NPE6cRhQGpmLegWOWXG7D3eYQ+lr1GFIGa/UOKimI4CxZjNLpTOxmgyIAz4AB3l D/0mIAufA61ixWJblF7IMUQTBaWZtEUvpifRUrgwYVJuv9o/6ZMyHIiFEZQkyrf6 MbmAVIpTZYZV0/vIfY2VlEDV0OxsKur/XnvE20TmsrG7auVQP5k9EfYKfrk02I7/ IFF4kCO7s2Uf6+reCnaG5fpFYzZHVUen4tRuNwLs+/lifIRUjCONazhudMu3tjlv 1R88wPVrdrHejx39lJ1exw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:content-type:date:date:feedback-id:feedback-id :from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:subject:subject:to:to:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm3; t=1778105982; x= 1778192382; bh=+uCojCTKCMOFVIV59W7fSxyYCD3fDWoJOIKPEBSOamQ=; b=R 98w9VOARBcxVEGmiXkiPnIBsBldJHOUwe1RZ7XQDk6Y6s03qLHZTLNSXJNQRoTan iG/YAu493ACmUIy4VRP2L3HneyOBiSgyGVQaQmMIIwsPCmLRxTSfAFnJ1E+diIUA s/nYD76n/uwitCK2si/fLSoNRe9VWiY/SoPaIpmt43ImdZwn1XcoAItTHOl04g76 aoxIC4WWPFEJQcs5iIkMnueAHpKID5oHDckVlxBkETOKZs3Q2JFIxqoNTy26xFor 3t7i3GRfsdmMxZoJRo12uGGlCsk7T+Uy4/OeM4r78C6eNrnYRNymULer66E6QgnU Iq0R6MQKN/4SGtHiiwSpg== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefhedrtddtgddutdehjeejucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucgopfhokfffucdluddtmdenucfjughrpefotggggffhvf ffufevjghfsehtkedttdertdejnecuhfhrohhmpeflrghvihgvrhcuvfhirgcuoehflhho shhssehjvghtmhdrmhgvqeenucggtffrrghtthgvrhhnpedtudejffejkeekteelueefvd ejvdeuhfefteehkeevtddvleduteekleetvdelhfenucevlhhushhtvghrufhiiigvpedt necurfgrrhgrmhepmhgrihhlfhhrohhmpehflhhoshhssehjvghtmhdrmhgvpdhnsggprh gtphhtthhopeehpdhmohguvgepshhmthhpohhuthdprhgtphhtthhopegsrghrnhgrsggr shdrphhotgiivgesihguvggrshhonhgsohgrrhgurdgtohhmpdhrtghpthhtohepkhhivg hrrghnrdgsihhnghhhrghmsehiuggvrghsohhnsghorghrugdrtghomhdprhgtphhtthho pehlihgstggrmhgvrhgrqdguvghvvghlsehlihhsthhsrdhlihgstggrmhgvrhgrrdhorh hgpdhrtghpthhtohepjhhohhgrnhhnvghsrdhgohgvuggvsehoshhsrdhquhgrlhgtohhm mhdrtghomhdprhgtphhtthhopehmiigrmhgriigrlhesrhgvughhrghtrdgtohhm X-ME-Proxy: Feedback-ID: i9dde48b3:Fastmail Received: by mailuser.phl.internal (Postfix, from userid 501) id 55C4F1EA006B; Wed, 6 May 2026 18:19:42 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 From: Javier Tia To: libcamera-devel@lists.libcamera.org Date: Wed, 06 May 2026 15:46:01 -0600 Subject: [PATCH v5 1/3] ipa: simple: agc: Replace bang-bang controller with proportional Cc: mzamazal@redhat.com, barnabas.pocze@ideasonboard.com, kieran.bingham@ideasonboard.com, johannes.goede@oss.qualcomm.com In-Reply-To: <177810597783.688418.1631246733707368646@jetm.me> References: <177810597783.688418.1631246733707368646@jetm.me> Message-Id: <20260506221942.55C4F1EA006B@mailuser.phl.internal> X-BeenThere: libcamera-devel@lists.libcamera.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libcamera-devel-bounces@lists.libcamera.org Sender: "libcamera-devel" The AGC's updateExposure() uses a fixed ~10% step per frame regardless of how far the current exposure is from optimal. With a hysteresis dead band of only +/-4%, the controller overshoots when the correct value falls within one step, causing visible brightness oscillation (flicker). Replace the fixed-step bang-bang controller with a proportional one where the correction factor scales linearly with the MSV error: factor = 1.0 + clamp(error * 0.04, -0.15, +0.15) At maximum error (~2.5), this gives the same ~10% step as before. Near the target, steps shrink to <1%, eliminating overshoot. The step is clamped to +/-15% to bound corrections when the scene changes dramatically. The existing hysteresis (kExposureSatisfactory) still prevents hunting on noise. Tested on OV2740 behind Intel IPU6 ISYS (ThinkPad X1 Carbon Gen 10) where the old controller produced continuous brightness flicker. The proportional controller converges in ~3 seconds from cold start with no visible oscillation. Signed-off-by: Javier Tia Reviewed-by: Milan Zamazal Tested-by: Barnabás Pőcze --- src/ipa/simple/algorithms/agc.cpp | 73 +++++++++++++++++++++---------- 1 file changed, 49 insertions(+), 24 deletions(-) diff --git a/src/ipa/simple/algorithms/agc.cpp b/src/ipa/simple/algorithms/agc.cpp index 2f7e040c..a13a7552 100644 --- a/src/ipa/simple/algorithms/agc.cpp +++ b/src/ipa/simple/algorithms/agc.cpp @@ -7,6 +7,8 @@ #include "agc.h" +#include +#include #include #include @@ -37,52 +39,74 @@ static constexpr float kExposureOptimal = kExposureBinsCount / 2.0; */ static constexpr float kExposureSatisfactory = 0.2; +/* + * Proportional gain for exposure/gain adjustment. Maps the MSV error to a + * multiplicative correction factor: + * + * factor = 1.0 + kExpProportionalGain * error + * + * With kExpProportionalGain = 0.04: + * - max error ~2.5 -> factor 1.10 (~10% step, same as before) + * - error 1.0 -> factor 1.04 (~4% step) + * - error 0.3 -> factor 1.012 (~1.2% step) + * + * This replaces the fixed 10% bang-bang step with a proportional correction + * that converges smoothly and avoids overshooting near the target. + */ +static constexpr float kExpProportionalGain = 0.04; + +/* + * Maximum multiplicative step per frame, to bound the correction when the + * scene changes dramatically. + */ +static constexpr float kExpMaxStep = 0.15; + Agc::Agc() { } void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, double exposureMSV) { - /* - * kExpDenominator of 10 gives ~10% increment/decrement; - * kExpDenominator of 5 - about ~20% - */ - static constexpr uint8_t kExpDenominator = 10; - static constexpr uint8_t kExpNumeratorUp = kExpDenominator + 1; - static constexpr uint8_t kExpNumeratorDown = kExpDenominator - 1; - int32_t &exposure = frameContext.sensor.exposure; double &again = frameContext.sensor.gain; - if (exposureMSV < kExposureOptimal - kExposureSatisfactory) { + double error = kExposureOptimal - exposureMSV; + + if (std::abs(error) <= kExposureSatisfactory) + return; + + /* + * Compute a proportional correction factor. The sign of the error + * determines the direction: positive error means too dark (increase), + * negative means too bright (decrease). + */ + float step = std::clamp(static_cast(error) * kExpProportionalGain, + -kExpMaxStep, kExpMaxStep); + float factor = 1.0f + step; + + if (factor > 1.0f) { + /* Scene too dark: increase exposure first, then gain. */ if (exposure < context.configuration.agc.exposureMax) { - int32_t next = exposure * kExpNumeratorUp / kExpDenominator; - if (next - exposure < 1) - exposure += 1; - else - exposure = next; + int32_t next = static_cast(exposure * factor); + exposure = std::max(next, exposure + 1); } else { - double next = again * kExpNumeratorUp / kExpDenominator; + double next = again * factor; if (next - again < context.configuration.agc.againMinStep) again += context.configuration.agc.againMinStep; else again = next; } - } - - if (exposureMSV > kExposureOptimal + kExposureSatisfactory) { + } else { + /* Scene too bright: decrease gain first, then exposure. */ if (again > context.configuration.agc.again10) { - double next = again * kExpNumeratorDown / kExpDenominator; + double next = again * factor; if (again - next < context.configuration.agc.againMinStep) again -= context.configuration.agc.againMinStep; else again = next; } else { - int32_t next = exposure * kExpNumeratorDown / kExpDenominator; - if (exposure - next < 1) - exposure -= 1; - else - exposure = next; + int32_t next = static_cast(exposure * factor); + exposure = std::min(next, exposure - 1); } } @@ -96,6 +120,7 @@ void Agc::updateExposure(IPAContext &context, IPAFrameContext &frameContext, dou LOG(IPASoftExposure, Debug) << "exposureMSV " << exposureMSV + << " error " << error << " factor " << factor << " exp " << exposure << " again " << again; }