libcamera: software_isp: Move black level to an algorithm module

The black level determination, already present as a separate class, can
be moved to the prepared Algorithm processing structure.  It is the
first of the current software ISP algorithms that is called in the stats
processing sequence, which means it is also the first one that should be
moved to the new structure.  Stats processing starts with calling
Algorithm-based processing so the call order of the algorithms is
retained.

Movement of this algorithm is relatively straightforward because all it
does is processing stats.

The comment about getting black level from the tuning files is dropped.
The black level will be taken from CameraSensorHelper if available and
that will be implemented in one of the followup patches.

Black level is now recomputed on each stats processing.  In a future
patch, after DelayedControls are used, this will be changed to recompute
the black level only after exposure/gain changes.

The black level depends on the sensor used, the computed value can be
reused in a followup capture sessions with the same sensor.  Thus it is
sufficient to (re)set the initial value in BlackLevel::init.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/simple/algorithms/blc.cpp

@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Red Hat Inc.
+ *
+ * Black level handling
+ */
+
+#include "blc.h"
+
+#include <numeric>
+
+#include <libcamera/base/log.h>
+
+namespace libcamera {
+
+namespace ipa::soft::algorithms {
+
+LOG_DEFINE_CATEGORY(IPASoftBL)
+
+BlackLevel::BlackLevel()
+{
+}
+
+int BlackLevel::configure(IPAContext &context,
+			  [[maybe_unused]] const IPAConfigInfo &configInfo)
+{
+	context.activeState.blc.level = 255;
+	return 0;
+}
+
+void BlackLevel::process(IPAContext &context,
+			 [[maybe_unused]] const uint32_t frame,
+			 [[maybe_unused]] IPAFrameContext &frameContext,
+			 const SwIspStats *stats,
+			 [[maybe_unused]] ControlList &metadata)
+{
+	const SwIspStats::Histogram &histogram = stats->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(histogram), end(histogram), 0);
+	const unsigned int pixelThreshold = ignoredPercentage * total;
+	const unsigned int histogramRatio = 256 / SwIspStats::kYHistogramSize;
+	const unsigned int currentBlackIdx =
+		context.activeState.blc.level / histogramRatio;
+
+	for (unsigned int i = 0, seen = 0;
+	     i < currentBlackIdx && i < SwIspStats::kYHistogramSize;
+	     i++) {
+		seen += histogram[i];
+		if (seen >= pixelThreshold) {
+			context.activeState.blc.level = i * histogramRatio;
+			LOG(IPASoftBL, Debug)
+				<< "Auto-set black level: "
+				<< i << "/" << SwIspStats::kYHistogramSize
+				<< " (" << 100 * (seen - histogram[i]) / total << "% below, "
+				<< 100 * seen / total << "% at or below)";
+			break;
+		}
+	};
+}
+
+REGISTER_IPA_ALGORITHM(BlackLevel, "BlackLevel")
+
+} /* namespace ipa::soft::algorithms */
+
+} /* namespace libcamera */

src/ipa/simple/algorithms/blc.h

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Red Hat Inc.
+ *
+ * Black level handling
+ */
+
+#pragma once
+
+#include "algorithm.h"
+
+namespace libcamera {
+
+namespace ipa::soft::algorithms {
+
+class BlackLevel : public Algorithm
+{
+public:
+	BlackLevel();
+	~BlackLevel() = default;
+
+	int configure(IPAContext &context, const IPAConfigInfo &configInfo) override;
+	void process(IPAContext &context, const uint32_t frame,
+		     IPAFrameContext &frameContext,
+		     const SwIspStats *stats,
+		     ControlList &metadata) override;
+};
+
+} /* namespace ipa::soft::algorithms */
+
+} /* namespace libcamera */

src/ipa/simple/algorithms/meson.build

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: CC0-1.0
 
 soft_simple_ipa_algorithms = files([
+    'blc.cpp',
 ])

src/ipa/simple/black_level.cpp

@@ -1,93 +0,0 @@
-/* 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)
-
-namespace ipa::soft {
-
-/**
- * \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 ipa::soft */
-
-} /* namespace libcamera */

src/ipa/simple/black_level.h

@@ -1,33 +0,0 @@
-/* SPDX-License-Identifier: LGPL-2.1-or-later */
-/*
- * Copyright (C) 2024, Red Hat Inc.
- *
- * black level handling
- */
-
-#pragma once
-
-#include <array>
-#include <stdint.h>
-
-#include "libcamera/internal/software_isp/swisp_stats.h"
-
-namespace libcamera {
-
-namespace ipa::soft {
-
-class BlackLevel
-{
-public:
-	BlackLevel();
-	uint8_t get() const;
-	void update(SwIspStats::Histogram &yHistogram);
-
-private:
-	uint8_t blackLevel_;
-	bool blackLevelSet_;
-};
-
-} /* namespace ipa::soft */
-
-} /* namespace libcamera */

src/ipa/simple/data/uncalibrated.yaml

@@ -3,4 +3,5 @@
 ---
 version: 1
 algorithms:
+  - BlackLevel:
 ...

src/ipa/simple/ipa_context.cpp

@@ -50,4 +50,12 @@ namespace libcamera::ipa::soft {
  * \brief The current state of IPA algorithms
  */
 
+/**
+ * \var IPAActiveState::black
+ * \brief Context for the Black Level algorithm
+ *
+ * \var IPAActiveState::black.level
+ * \brief Current determined black level
+ */
+
 } /* namespace libcamera::ipa::soft */

src/ipa/simple/ipa_context.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <stdint.h>
+
 #include <libipa/fc_queue.h>
 
 namespace libcamera {
@@ -17,6 +19,9 @@ struct IPASessionConfiguration {
 };
 
 struct IPAActiveState {
+	struct {
+		uint8_t level;
+	} blc;
 };
 
 struct IPAFrameContext : public FrameContext {

src/ipa/simple/meson.build

@@ -8,7 +8,6 @@ ipa_name = 'ipa_soft_simple'
 soft_simple_sources = files([
     'ipa_context.cpp',
     'soft_simple.cpp',
-    'black_level.cpp',
 ])
 
 soft_simple_sources += soft_simple_ipa_algorithms

src/ipa/simple/soft_simple.cpp

@@ -29,7 +29,6 @@
 
 #include "libipa/camera_sensor_helper.h"
 
-#include "black_level.h"
 #include "module.h"
 
 namespace libcamera {
@@ -61,7 +60,7 @@ class IPASoftSimple : public ipa::soft::IPASoftInterface, public Module
 {
 public:
 	IPASoftSimple()
-		: params_(nullptr), stats_(nullptr), blackLevel_(BlackLevel()),
+		: params_(nullptr), stats_(nullptr),
 		  context_({ {}, {}, { kMaxFrameContexts } }),
 		  ignoreUpdates_(0)
 	{
@@ -93,7 +92,6 @@ private:
 	SwIspStats *stats_;
 	std::unique_ptr<CameraSensorHelper> camHelper_;
 	ControlInfoMap sensorInfoMap_;
-	BlackLevel blackLevel_;
 
 	static constexpr unsigned int kGammaLookupSize = 1024;
 	std::array<uint8_t, kGammaLookupSize> gammaTable_;
@@ -303,9 +301,7 @@ void IPASoftSimple::processStats(const uint32_t frame,
 		algo->process(context_, frame, frameContext, stats_, metadata);
 
 	SwIspStats::Histogram histogram = stats_->yHistogram;
-	if (ignoreUpdates_ > 0)
+	const uint8_t blackLevel = context_.activeState.blc.level;
-		blackLevel_.update(histogram);
-	const uint8_t blackLevel = blackLevel_.get();
 
 	/*
 	 * Black level must be subtracted to get the correct AWB ratios, they