From b2ef255295871fb6246d99bdd5b41aa65e3fc3b2 Mon Sep 17 00:00:00 2001 From: Milan Zamazal Date: Tue, 16 Apr 2024 11:13:54 +0200 Subject: libcamera: software_isp: Apply black level compensation Black may not be represented as 0 pixel value for given hardware, it may be higher. If this is not compensated then various problems may occur such as low contrast or suboptimal exposure. The black pixel value can be either retrieved from a tuning file for the given hardware, or automatically on the fly. The former is the right and correct method, while the latter can be used when a tuning file is not available for the given hardware. Since there is currently no support for tuning files in software ISP, the automatic, hardware independent way, is always used. Support for tuning files should be added in future but it will require more work than this patch. The patch looks at the image histogram and assumes that black starts when pixel values start occurring on the left. A certain amount of the darkest pixels is ignored; it doesn't matter whether they represent various kinds of noise or are real, they are better to omit in any case to make the image looking better. It also doesn't matter whether the darkest pixels occur around the supposed black level or are spread between 0 and the black level, the difference is not important. An arbitrary threshold of 2% darkest pixels is applied; there is no magic about that value. The patch assumes that the black values for different colors are the same and doesn't attempt any other non-primitive enhancements. It cannot completely replace tuning files and simplicity, while providing visible benefit, is its goal. Anything more sophisticated is left for future patches. A possible cheap enhancement, if needed, could be setting exposure + gain to minimum values temporarily, before setting the black level. In theory, the black level should be fixed but it may not be reached in all images. For this reason, the patch updates black level only if the observed value is lower than the current one; it should be never increased. The purpose of the patch is to compensate for hardware properties. General image contrast enhancements are out of scope of this patch. Stats are still gathered as an uncorrected histogram, to avoid any confusion and to represent the raw image data. Exposure must be determined after the black level correction -- it has no influence on the sub-black area and must be correct after applying the black level correction. The granularity of the histogram is increased from 16 to 64 to provide a better precision (there is no theory behind either of those numbers). Reviewed-by: Hans de Goede Signed-off-by: Milan Zamazal Signed-off-by: Hans de Goede Signed-off-by: Milan Zamazal Signed-off-by: Kieran Bingham --- src/ipa/simple/black_level.cpp | 88 ++++++++++++++++++++++++++++++++++++++++++ src/ipa/simple/black_level.h | 28 ++++++++++++++ src/ipa/simple/meson.build | 7 +++- src/ipa/simple/soft_simple.cpp | 30 +++++++++----- 4 files changed, 142 insertions(+), 11 deletions(-) create mode 100644 src/ipa/simple/black_level.cpp create mode 100644 src/ipa/simple/black_level.h (limited to 'src/ipa/simple') diff --git a/src/ipa/simple/black_level.cpp b/src/ipa/simple/black_level.cpp new file mode 100644 index 00000000..c7e8d8b7 --- /dev/null +++ b/src/ipa/simple/black_level.cpp @@ -0,0 +1,88 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ +/* + * Copyright (C) 2024, Red Hat Inc. + * + * black_level.cpp - black level handling + */ + +#include "black_level.h" + +#include + +#include + +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. + */ +unsigned int 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 */ diff --git a/src/ipa/simple/black_level.h b/src/ipa/simple/black_level.h new file mode 100644 index 00000000..7e37757e --- /dev/null +++ b/src/ipa/simple/black_level.h @@ -0,0 +1,28 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ +/* + * Copyright (C) 2024, Red Hat Inc. + * + * black_level.h - black level handling + */ + +#pragma once + +#include + +#include "libcamera/internal/software_isp/swisp_stats.h" + +namespace libcamera { + +class BlackLevel +{ +public: + BlackLevel(); + unsigned int get() const; + void update(SwIspStats::Histogram &yHistogram); + +private: + unsigned int blackLevel_; + bool blackLevelSet_; +}; + +} /* namespace libcamera */ diff --git a/src/ipa/simple/meson.build b/src/ipa/simple/meson.build index 3e863db7..44b5f1d7 100644 --- a/src/ipa/simple/meson.build +++ b/src/ipa/simple/meson.build @@ -2,8 +2,13 @@ ipa_name = 'ipa_soft_simple' +soft_simple_sources = files([ + 'soft_simple.cpp', + 'black_level.cpp', +]) + mod = shared_module(ipa_name, - ['soft_simple.cpp', libcamera_generated_ipa_headers], + [soft_simple_sources, libcamera_generated_ipa_headers], name_prefix : '', include_directories : [ipa_includes, libipa_includes], dependencies : libcamera_private, diff --git a/src/ipa/simple/soft_simple.cpp b/src/ipa/simple/soft_simple.cpp index ff1d8e0c..b9fb58b5 100644 --- a/src/ipa/simple/soft_simple.cpp +++ b/src/ipa/simple/soft_simple.cpp @@ -26,8 +26,9 @@ #include "libipa/camera_sensor_helper.h" -namespace libcamera { +#include "black_level.h" +namespace libcamera { LOG_DEFINE_CATEGORY(IPASoft) namespace ipa::soft { @@ -54,7 +55,8 @@ class IPASoftSimple : public ipa::soft::IPASoftInterface { public: IPASoftSimple() - : params_(nullptr), stats_(nullptr), ignoreUpdates_(0) + : params_(nullptr), stats_(nullptr), blackLevel_(BlackLevel()), + ignoreUpdates_(0) { } @@ -78,6 +80,7 @@ private: SwIspStats *stats_; std::unique_ptr camHelper_; ControlInfoMap sensorInfoMap_; + BlackLevel blackLevel_; int32_t exposureMin_, exposureMax_; int32_t exposure_; @@ -255,6 +258,10 @@ void IPASoftSimple::processStats(const ControlList &sensorControls) params_->gainG = 256; params_->gamma = 0.5; + if (ignoreUpdates_ > 0) + blackLevel_.update(stats_->yHistogram); + params_->blackLevel = blackLevel_.get(); + setIspParams.emit(); /* \todo Switch to the libipa/algorithm.h API someday. */ @@ -273,18 +280,20 @@ void IPASoftSimple::processStats(const ControlList &sensorControls) * Calculate Mean Sample Value (MSV) according to formula from: * https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf */ - constexpr unsigned int yHistValsPerBin = - SwIspStats::kYHistogramSize / kExposureBinsCount; - constexpr unsigned int yHistValsPerBinMod = - SwIspStats::kYHistogramSize / - (SwIspStats::kYHistogramSize % kExposureBinsCount + 1); + const unsigned int blackLevelHistIdx = + params_->blackLevel / (256 / SwIspStats::kYHistogramSize); + const unsigned int histogramSize = + SwIspStats::kYHistogramSize - blackLevelHistIdx; + const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount; + const unsigned int yHistValsPerBinMod = + histogramSize / (histogramSize % kExposureBinsCount + 1); int exposureBins[kExposureBinsCount] = {}; unsigned int denom = 0; unsigned int num = 0; - for (unsigned int i = 0; i < SwIspStats::kYHistogramSize; i++) { + for (unsigned int i = 0; i < histogramSize; i++) { unsigned int idx = (i - (i / yHistValsPerBinMod)) / yHistValsPerBin; - exposureBins[idx] += stats_->yHistogram[i]; + exposureBins[idx] += stats_->yHistogram[blackLevelHistIdx + i]; } for (unsigned int i = 0; i < kExposureBinsCount; i++) { @@ -320,7 +329,8 @@ void IPASoftSimple::processStats(const ControlList &sensorControls) LOG(IPASoft, Debug) << "exposureMSV " << exposureMSV << " exp " << exposure_ << " again " << again_ - << " gain R/B " << params_->gainR << "/" << params_->gainB; + << " gain R/B " << params_->gainR << "/" << params_->gainB + << " black level " << params_->blackLevel; } void IPASoftSimple::updateExposure(double exposureMSV) -- cgit v1.2.1