From 07240afa12d2fb44f811aebdadb7dea200a9dd3a Mon Sep 17 00:00:00 2001 From: Milan Zamazal Date: Tue, 27 Jan 2026 21:47:11 +0100 Subject: [PATCH] libcamera: simple: Fix black level offsets in AWB The black level offset subtracted in AWB is wrong. It assumes that the stats contain sums of the individual colour pixels. But they actually contain sums of the colour channels of larger "superpixels" consisting of the individual colour pixels. Each of the RGB colour values and the computed luminosity (a histogram entry) are added once to the stats per such a superpixel. This means the offset computed from the black level and the number of pixels should be used as it is, not divided. The patch fixes the subtracted offset. Since the evaluation is the same for all the three colours now, the individual class variables are replaced with a single RGB variable. Fixes: 4e13c6f55bd667 ("Honor black level in AWB") Reviewed-by: Laurent Pinchart Reviewed-by: Robert Mader Tested-by: Robert Mader Signed-off-by: Milan Zamazal Signed-off-by: Kieran Bingham --- .../internal/software_isp/swisp_stats.h | 16 +++++----------- src/ipa/simple/algorithms/awb.cpp | 14 ++++++++------ src/libcamera/software_isp/swstats_cpu.cpp | 10 ++++------ 3 files changed, 17 insertions(+), 23 deletions(-) diff --git a/include/libcamera/internal/software_isp/swisp_stats.h b/include/libcamera/internal/software_isp/swisp_stats.h index 3c986018..d9d0d9be 100644 --- a/include/libcamera/internal/software_isp/swisp_stats.h +++ b/include/libcamera/internal/software_isp/swisp_stats.h @@ -10,6 +10,8 @@ #include #include +#include "libcamera/internal/vector.h" + namespace libcamera { /** @@ -26,17 +28,9 @@ struct SwIspStats { */ bool valid; /** - * \brief Holds the sum of all sampled red pixels + * \brief Sums of colour channels of all the sampled pixels */ - uint64_t sumR_; - /** - * \brief Holds the sum of all sampled green pixels - */ - uint64_t sumG_; - /** - * \brief Holds the sum of all sampled blue pixels - */ - uint64_t sumB_; + RGB sum_; /** * \brief Number of bins in the yHistogram */ @@ -46,7 +40,7 @@ struct SwIspStats { */ using Histogram = std::array; /** - * \brief A histogram of luminance values + * \brief A histogram of luminance values of all the sampled pixels */ Histogram yHistogram; }; diff --git a/src/ipa/simple/algorithms/awb.cpp b/src/ipa/simple/algorithms/awb.cpp index 0080865a..50565fe8 100644 --- a/src/ipa/simple/algorithms/awb.cpp +++ b/src/ipa/simple/algorithms/awb.cpp @@ -1,6 +1,6 @@ /* SPDX-License-Identifier: LGPL-2.1-or-later */ /* - * Copyright (C) 2024, Red Hat Inc. + * Copyright (C) 2024-2026 Red Hat Inc. * * Auto white balance */ @@ -73,9 +73,11 @@ void Awb::process(IPAContext &context, histogram.begin(), histogram.end(), uint64_t(0)); const uint64_t offset = blackLevel * nPixels; const uint64_t minValid = 1; - const uint64_t sumR = stats->sumR_ > offset / 4 ? stats->sumR_ - offset / 4 : minValid; - const uint64_t sumG = stats->sumG_ > offset / 2 ? stats->sumG_ - offset / 2 : minValid; - const uint64_t sumB = stats->sumB_ > offset / 4 ? stats->sumB_ - offset / 4 : minValid; + /* + * Make sure the sums are at least minValid, while preventing unsigned + * integer underflow. + */ + const RGB sum = stats->sum_.max(offset + minValid) - offset; /* * Calculate red and blue gains for AWB. @@ -83,9 +85,9 @@ void Awb::process(IPAContext &context, */ auto &gains = context.activeState.awb.gains; gains = { { - sumR <= sumG / 4 ? 4.0f : static_cast(sumG) / sumR, + sum.r() <= sum.g() / 4 ? 4.0f : static_cast(sum.g()) / sum.r(), 1.0, - sumB <= sumG / 4 ? 4.0f : static_cast(sumG) / sumB, + sum.b() <= sum.g() / 4 ? 4.0f : static_cast(sum.g()) / sum.b(), } }; RGB rgbGains{ { 1 / gains.r(), 1 / gains.g(), 1 / gains.b() } }; diff --git a/src/libcamera/software_isp/swstats_cpu.cpp b/src/libcamera/software_isp/swstats_cpu.cpp index c931edb4..5c3011a7 100644 --- a/src/libcamera/software_isp/swstats_cpu.cpp +++ b/src/libcamera/software_isp/swstats_cpu.cpp @@ -185,9 +185,9 @@ static constexpr unsigned int kBlueYMul = 29; /* 0.114 * 256 */ stats_.yHistogram[yVal * SwIspStats::kYHistogramSize / (256 * 256 * (div))]++; #define SWSTATS_FINISH_LINE_STATS() \ - stats_.sumR_ += sumR; \ - stats_.sumG_ += sumG; \ - stats_.sumB_ += sumB; + stats_.sum_.r() += sumR; \ + stats_.sum_.g() += sumG; \ + stats_.sum_.b() += sumB; void SwStatsCpu::statsBGGR8Line0(const uint8_t *src[]) { @@ -332,9 +332,7 @@ void SwStatsCpu::startFrame(uint32_t frame) if (window_.width == 0) LOG(SwStatsCpu, Error) << "Calling startFrame() without setWindow()"; - stats_.sumR_ = 0; - stats_.sumB_ = 0; - stats_.sumG_ = 0; + stats_.sum_ = RGB({ 0, 0, 0 }); stats_.yHistogram.fill(0); }