/* SPDX-License-Identifier: LGPL-2.1-or-later */ /* * Copyright (C) 2024, Red Hat Inc. * * black level handling */ #include "black_level.h" #include <numeric> #include <libcamera/base/log.h> namespace libcamera { LOG_DEFINE_CATEGORY(IPASoftBL) /** * \class BlackLevel * \brief Object providing black point level for software ISP * * Black level can be provided in hardware tuning files or, if no tuning file is * available for the given hardware, guessed automatically, with less accuracy. * As tuning files are not yet implemented for software ISP, BlackLevel * currently provides only guessed black levels. * * This class serves for tracking black level as a property of the underlying * hardware, not as means of enhancing a particular scene or image. * * The class is supposed to be instantiated for the given camera stream. * The black level can be retrieved using BlackLevel::get() method. It is * initially 0 and may change when updated using BlackLevel::update() method. */ BlackLevel::BlackLevel() : blackLevel_(255), blackLevelSet_(false) { } /** * \brief Return the current black level * * \return The black level, in the range from 0 (minimum) to 255 (maximum). * If the black level couldn't be determined yet, return 0. */ uint8_t BlackLevel::get() const { return blackLevelSet_ ? blackLevel_ : 0; } /** * \brief Update black level from the provided histogram * \param[in] yHistogram The histogram to be used for updating black level * * The black level is property of the given hardware, not image. It is updated * only if it has not been yet set or if it is lower than the lowest value seen * so far. */ void BlackLevel::update(SwIspStats::Histogram &yHistogram) { /* * The constant is selected to be "good enough", not overly conservative or * aggressive. There is no magic about the given value. */ constexpr float ignoredPercentage_ = 0.02; const unsigned int total = std::accumulate(begin(yHistogram), end(yHistogram), 0); const unsigned int pixelThreshold = ignoredPercentage_ * total; const unsigned int histogramRatio = 256 / SwIspStats::kYHistogramSize; const unsigned int currentBlackIdx = blackLevel_ / histogramRatio; for (unsigned int i = 0, seen = 0; i < currentBlackIdx && i < SwIspStats::kYHistogramSize; i++) { seen += yHistogram[i]; if (seen >= pixelThreshold) { blackLevel_ = i * histogramRatio; blackLevelSet_ = true; LOG(IPASoftBL, Debug) << "Auto-set black level: " << i << "/" << SwIspStats::kYHistogramSize << " (" << 100 * (seen - yHistogram[i]) / total << "% below, " << 100 * seen / total << "% at or below)"; break; } }; } } /* namespace libcamera */