From patchwork Thu Aug 20 15:19:09 2026 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= X-Patchwork-Id: 27944 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 E972AC3336 for ; Thu, 20 Aug 2026 15:20:32 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id 64100683B9; Thu, 20 Aug 2026 17:20:32 +0200 (CEST) Authentication-Results: lancelot.ideasonboard.com; dkim=pass (1024-bit key; unprotected) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="PRqxFUtp"; dkim-atps=neutral Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lancelot.ideasonboard.com (Postfix) with ESMTPS id 1023A6836B for ; Thu, 20 Aug 2026 17:19:32 +0200 (CEST) Received: from pb-laptop.local (185.221.143.32.nat.pool.zt.hu [185.221.143.32]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 82EF52913; Thu, 20 Aug 2026 17:18:10 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1787239090; bh=FnMetkbuTtDJP0B+/vGMVrdp4YO0L6W2sYPhQ/63o9k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PRqxFUtp6GMl6y3MeCW1+pkXm7L8ypArMIbLC4sxVDC//cXYu2LgbVIiesORQRKMh XaLIBv7DkWKYdA3ID4SVxDZjeXg+lGxkhumxA/pILsDI4FJuPeq96ogZlcW/A5h9FH eYlSCj98+QIi05cniCr2P066jXzNfrLGILLJBBbA= From: =?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= To: libcamera-devel@lists.libcamera.org Cc: Milan Zamazal Subject: [PATCH v6 39/47] ipa: softisp: agc: Adjust histogram for black level Date: Thu, 20 Aug 2026 17:19:09 +0200 Message-ID: <20260820151918.2382337-40-barnabas.pocze@ideasonboard.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260820151918.2382337-1-barnabas.pocze@ideasonboard.com> References: <20260820151918.2382337-1-barnabas.pocze@ideasonboard.com> MIME-Version: 1.0 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" Instead of providing the black separately, adjust the luminance histogram according to the current black level. Everything under the black level is summed into the bin corresponding to the current black level, and the MSV calculation is carried out on the partial histogram that starts at the bin of the black level. This changes the behaviour slightly as previously everything under the black level was ignored, and only the remaining part was split into the 5 bins, but now the ignored bins are instead summed into the "first" bin of the "new" histogram. This can result in the same image with the same statistics being perceived as darker by the algorithm. Signed-off-by: Barnabás Pőcze Reviewed-by: Milan Zamazal --- src/ipa/softisp/algorithms/agc.cpp | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/src/ipa/softisp/algorithms/agc.cpp b/src/ipa/softisp/algorithms/agc.cpp index 0027365b33..a9dce466a9 100644 --- a/src/ipa/softisp/algorithms/agc.cpp +++ b/src/ipa/softisp/algorithms/agc.cpp @@ -66,19 +66,15 @@ static constexpr float kExpMaxStep = 0.15; namespace { -std::optional calculateMSV(const Histogram &histogram, uint8_t blackLevel) +std::optional calculateMSV(const Histogram &histogram) { /* * Calculate Mean Sample Value (MSV) according to formula from: * https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf */ - const unsigned int blackLevelHistIdx = - blackLevel * histogram.bins() / 256; - const unsigned int histogramSize = - histogram.bins() - blackLevelHistIdx; - const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount; + const unsigned int yHistValsPerBin = histogram.bins() / kExposureBinsCount; const unsigned int yHistValsPerBinMod = - histogramSize / (histogramSize % kExposureBinsCount + 1); + histogram.bins() / (histogram.bins() % kExposureBinsCount + 1); int exposureBins[kExposureBinsCount] = {}; unsigned int denom = 0; unsigned int num = 0; @@ -86,9 +82,9 @@ std::optional calculateMSV(const Histogram &histogram, uint8_t blackLevel if (yHistValsPerBin == 0) return std::nullopt; - for (unsigned int i = 0; i < histogramSize; i++) { + for (unsigned int i = 0; i < histogram.bins(); i++) { unsigned int idx = (i - (i / yHistValsPerBinMod)) / yHistValsPerBin; - exposureBins[idx] += histogram[blackLevelHistIdx + i]; + exposureBins[idx] += histogram[i]; } for (unsigned int i = 0; i < kExposureBinsCount; i++) { @@ -193,7 +189,14 @@ void Agc::process(IPAContext &context, return; } - auto exposureMSV = calculateMSV({ stats->yHistogram }, context.activeState.blc.level); + auto histogram = stats->yHistogram; + const unsigned int blackLevelHistIdx = + context.activeState.blc.level * std::size(histogram) / 256; + + for (unsigned int i = 0; i < blackLevelHistIdx; i++) + histogram[blackLevelHistIdx] += histogram[i]; + + auto exposureMSV = calculateMSV({ { histogram.begin() + blackLevelHistIdx, histogram.end() } }); if (!exposureMSV) { LOG(IPASoftIspExposure, Debug) << "Not adjusting exposure due to insufficient histogram data";