From patchwork Mon Aug 10 10:38:36 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: 27713 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 05AE2BDE4C for ; Mon, 10 Aug 2026 10:39:58 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id 8B90368252; Mon, 10 Aug 2026 12:39:57 +0200 (CEST) Authentication-Results: lancelot.ideasonboard.com; dkim=pass (1024-bit key; unprotected) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="RJNrFAyr"; 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 C0C33681FF for ; Mon, 10 Aug 2026 12:38:59 +0200 (CEST) Received: from pb-laptop.local (185.221.141.208.nat.pool.zt.hu [185.221.141.208]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id C0F8422EC for ; Mon, 10 Aug 2026 12:37:45 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1786358265; bh=9NOjIb4xxja4Q6fLfGmcIo6NzJ0zrrhk4uPqRlH65bE=; h=From:To:Subject:Date:In-Reply-To:References:From; b=RJNrFAyrjc0Cq1PPttQxUQ+tK5/tOCti9pilN9a5HINy3V7CnxtPJTEuuxS7D2dt7 j/18SsBsd0TCtUt5b2on9tYTZTiVClfq103TPJG7RTXK50fxUJgQwI8vr42qVDRFsh mDXqIptgbbOmNlgH2C8rkyaMsKR2Bf+mw7gz+7o4= From: =?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= To: libcamera-devel@lists.libcamera.org Subject: [PATCH v4 40/49] ipa: simple: agc: Adjust histogram for black level Date: Mon, 10 Aug 2026 12:38:36 +0200 Message-ID: <20260810103846.1075936-41-barnabas.pocze@ideasonboard.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260810103846.1075936-1-barnabas.pocze@ideasonboard.com> References: <20260810103846.1075936-1-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/simple/algorithms/agc.cpp | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/src/ipa/simple/algorithms/agc.cpp b/src/ipa/simple/algorithms/agc.cpp index e24eacde72..a3e0ebbc3d 100644 --- a/src/ipa/simple/algorithms/agc.cpp +++ b/src/ipa/simple/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 {}; - 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(IPASoftExposure, Debug) << "Not adjusting exposure due to insufficient histogram data";