1 files changed, 78 insertions, 0 deletions
diff --git a/src/ipa/simple/algorithms/blc.cpp b/src/ipa/simple/algorithms/blc.cpp
new file mode 100644
index 00000000..b9f2aaa6
--- /dev/null
+++ b/src/ipa/simple/algorithms/blc.cpp
@@ -0,0 +1,78 @@
+/* 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,
+			 IPAFrameContext &frameContext,
+			 const SwIspStats *stats,
+			 [[maybe_unused]] ControlList &metadata)
+{
+	if (frameContext.sensor.exposure == exposure_ &&
+	    frameContext.sensor.gain == gain_) {
+		return;
+	}
+
+	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;
+			exposure_ = frameContext.sensor.exposure;
+			gain_ = frameContext.sensor.gain;
+			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 */