[{"id":38667,"web_url":"https://patchwork.libcamera.org/comment/38667/","msgid":"<177747637532.45302.7432121546861212968@ping.linuxembedded.co.uk>","date":"2026-04-29T15:26:15","subject":"Re: [PATCH v4 2/3] libcamera: software_isp: Normalize statistics\n\tsums to 8-bit","submitter":{"id":4,"url":"https://patchwork.libcamera.org/api/people/4/","name":"Kieran Bingham","email":"kieran.bingham@ideasonboard.com"},"content":"Hi Javier,\n\n\nQuoting Javier Tia (2026-03-06 18:46:41)\n> The SWSTATS_ACCUMULATE_LINE_STATS() macro divides the luminance value\n> for the histogram to normalize it to 8-bit range, but does not apply\n> the same normalization to the RGB sums. For 10-bit and 12-bit unpacked\n> Bayer formats this means the sums are accumulated at native bit depth\n> (0-1023 or 0-4095 per pixel) while the AWB algorithm subtracts an\n> 8-bit black level from them, under-correcting by 4x or 16x\n> respectively.\n> \n> This mismatch between the AWB's gain calculation (using incorrectly\n> BLC-subtracted sums) and the debayer's correct normalized BLC\n> subtraction produces a visible color cast. For example, with the\n> OV2740 sensor (10-bit, BLC=16), the under-subtraction skews R/G gain\n> by ~9%.\n> \n> Fix this by right-shifting the RGB sums in finishFrame() to normalize\n> them to 8-bit scale, matching the histogram and the 8-bit black level\n> used by AWB. A per-format sumShift_ value is set in configure():\n> 0 for 8-bit and CSI-2 packed formats (already 8-bit), 2 for 10-bit,\n> and 4 for 12-bit unpacked formats.\n> \n> Signed-off-by: Javier Tia \n> Reviewed-by: Milan Zamazal \n> Tested-by: Milan Zamazal \n> Reviewed-by: Barnabás Pőcze \n> Tested-by: Barnabás Pőcze \n> ---\n> include/libcamera/internal/software_isp/swstats_cpu.h | 1 +\n> src/libcamera/software_isp/swstats_cpu.cpp | 7 +++++++\n> 2 files changed, 8 insertions(+)\n> \n> diff --git a/include/libcamera/internal/software_isp/swstats_cpu.h b/include/libcamera/internal/software_isp/swstats_cpu.h\n> index 64b3e23f..37bfde53 100644\n> --- a/include/libcamera/internal/software_isp/swstats_cpu.h\n> +++ b/include/libcamera/internal/software_isp/swstats_cpu.h\n> @@ -115,6 +115,7 @@ private:\n> \n> unsigned int xShift_;\n> unsigned int stride_;\n> + unsigned int sumShift_;\n> \n> SharedMemObject sharedStats_;\n> SwIspStats stats_;\n> diff --git a/src/libcamera/software_isp/swstats_cpu.cpp b/src/libcamera/software_isp/swstats_cpu.cpp\n> index 1cedcfbc..744a7560 100644\n> --- a/src/libcamera/software_isp/swstats_cpu.cpp\n> +++ b/src/libcamera/software_isp/swstats_cpu.cpp\n> @@ -346,6 +346,11 @@ void SwStatsCpu::startFrame(uint32_t frame)\n> void SwStatsCpu::finishFrame(uint32_t frame, uint32_t bufferId)\n> {\n> stats_.valid = frame % kStatPerNumFrames == 0;\n> + if (stats_.valid && sumShift_) {\n> + stats_.sum_.r() >>= sumShift_;\n> + stats_.sum_.g() >>= sumShift_;\n> + stats_.sum_.b() >>= sumShift_;\n> + }\n\nI was trying to get this merged, but unfortunately something changed\nhere.\n\nCould you take a look and rebase on v0.7.1 please to submit a v5, then I\nthink we should get this series merged.\n\nAlthough I think we could do somethign else for 3/3 - that could be done\nlater and on top.\n\nI'd be interested to know if this is the cure for the flicker - or if\nthe 3/3 patch is actually needed in fact.\n\n--\nKieran\n\n> *sharedStats_ = stats_;\n> statsReady.emit(frame, bufferId);\n> }\n> @@ -402,6 +407,7 @@ int SwStatsCpu::configure(const StreamConfiguration &inputCfg)\n> if (bayerFormat.packing == BayerFormat::Packing::None &&\n> setupStandardBayerOrder(bayerFormat.order) == 0) {\n> processFrame_ = &SwStatsCpu::processBayerFrame2;\n> + sumShift_ = bayerFormat.bitDepth - 8;\n> switch (bayerFormat.bitDepth) {\n> case 8:\n> stats0_ = &SwStatsCpu::statsBGGR8Line0;\n> @@ -422,6 +428,7 @@ int SwStatsCpu::configure(const StreamConfiguration &inputCfg)\n> /* Skip every 3th and 4th line, sample every other 2x2 block */\n> ySkipMask_ = 0x02;\n> xShift_ = 0;\n> + sumShift_ = 0;\n> processFrame_ = &SwStatsCpu::processBayerFrame2;\n> \n> switch (bayerFormat.order) {\n> \n> -- \n> 2.53.0\n>","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 15728BDCB5\n\tfor ;\n\tWed, 29 Apr 2026 15:26:22 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 009F262FD9;\n\tWed, 29 Apr 2026 17:26:20 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id CC64962010\n\tfor ;\n\tWed, 29 Apr 2026 17:26:18 +0200 (CEST)","from monstersaurus.ideasonboard.com\n\t(cpc89244-aztw30-2-0-cust6594.18-1.cable.virginm.net [86.31.185.195])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id EA41A4BB;\n\tWed, 29 Apr 2026 17:24:34 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"U5F6jnGP\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1777476275;\n\tbh=7dyqujgiqpr1Kzg87SPvyxIMZ9+yAznzwmQ1VEzS4TI=;\n\th=In-Reply-To:References:Subject:From:Cc:To:Date:From;\n\tb=U5F6jnGPOnklJP/hw7uHoeI7C4vxGlRe2hkA9d4UGdLRfOWoXX9fPYfL/jnkKUK1R\n\tolEKqxokqYrSK7m/qh0HtmfEP6gWXvnei4mKo613ujZKNCeEMvhBAoaxg5BP0ZyndV\n\tEYtyLOXZfzW7yzbe2tJ//Yl8AIMedXLwhS8VM+Ms=","Content-Type":"text/plain; charset=\"utf-8\"","MIME-Version":"1.0","Content-Transfer-Encoding":"quoted-printable","In-Reply-To":"<20260306-agc-proportional-v4-2-e87c7e0d837a@jetm.me>","References":"<20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me>\n\t<20260306-agc-proportional-v4-2-e87c7e0d837a@jetm.me>","Subject":"Re: [PATCH v4 2/3] libcamera: software_isp: Normalize statistics\n\tsums to 8-bit","From":"Kieran Bingham ","Cc":"Javier Tia , Milan Zamazal ,\n\t=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","To":"Javier Tia , libcamera-devel@lists.libcamera.org","Date":"Wed, 29 Apr 2026 16:26:15 +0100","Message-ID":"<177747637532.45302.7432121546861212968@ping.linuxembedded.co.uk>","User-Agent":"alot/0.9.1","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":38747,"web_url":"https://patchwork.libcamera.org/comment/38747/","msgid":"<20260506224252.C48E71EA006B@mailuser.phl.internal>","date":"2026-05-06T22:28:12","subject":"Re: [PATCH v4 2/3] libcamera: software_isp: Normalize statistics\n\tsums to 8-bit","submitter":{"id":261,"url":"https://patchwork.libcamera.org/api/people/261/","name":"Javier Tia","email":"floss@jetm.me"},"content":"Hi Kieran,\n\nThanks for the review. Rebased on current master for v5 - the diff\ncontext in finishFrame() changed because of the multi-threading\nrefactor (6e53e72e), which restructured the function to aggregate\nfrom a stats_ vector before applying the shift. No functional\nchanges to the patch itself.\n\nOn 3/3: I tested this on OV2740 (ThinkPad X1 Carbon Gen 10). Patch\n1/3 alone cures the flicker. A 40-frame capture with patches 1/3\nand 2/3 applied shows smooth monotonic brightness convergence from\nframe 4 onwards with no oscillation. Patch 3/3 (OV2740 BLC=16)\nimproves AWB color accuracy by providing the correct black level\nbaseline for channel gain calculation, but it is independent of the\nflicker fix.\n\nIncluding all three in v5 since 3/3 is a genuine calibration\nimprovement regardless.\n\nv5 has been sent:\nhttps://lists.libcamera.org/pipermail/libcamera-devel/2026-May/058560.html\n\nBest,\nJavier","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 AA2E0C32F6\n\tfor ;\n\tWed, 6 May 2026 22:42:56 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id A4DEB6301A;\n\tThu, 7 May 2026 00:42:55 +0200 (CEST)","from fout-a5-smtp.messagingengine.com\n\t(fout-a5-smtp.messagingengine.com [103.168.172.148])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 95CF262DC4\n\tfor ;\n\tThu, 7 May 2026 00:42:53 +0200 (CEST)","from phl-compute-02.internal (phl-compute-02.internal\n\t[10.202.2.42])\n\tby mailfout.phl.internal (Postfix) with ESMTP id E154AEC013B;\n\tWed, 6 May 2026 18:42:52 -0400 (EDT)","from phl-imap-07 ([10.202.2.97])\n\tby phl-compute-02.internal (MEProxy); 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charset=\"utf-8\"","MIME-Version":"1.0","Content-Transfer-Encoding":"8bit","From":"Javier Tia ","To":"Kieran Bingham ","Date":"Wed, 06 May 2026 16:28:12 -0600","Subject":"Re: [PATCH v4 2/3] libcamera: software_isp: Normalize statistics\n\tsums to 8-bit","Cc":"libcamera-devel@lists.libcamera.org, Milan Zamazal ,\n\t=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","In-Reply-To":"<177747637532.45302.7432121546861212968@ping.linuxembedded.co.uk>","References":"<20260306-agc-proportional-v4-0-e87c7e0d837a@jetm.me>\n\t<20260306-agc-proportional-v4-2-e87c7e0d837a@jetm.me>\n\t<177747637532.45302.7432121546861212968@ping.linuxembedded.co.uk>","Message-Id":"<20260506224252.C48E71EA006B@mailuser.phl.internal>","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]