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diff --git a/src/ipa/raspberrypi/controller/rpi/noise.cpp b/src/ipa/raspberrypi/controller/rpi/noise.cpp
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+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2019, Raspberry Pi (Trading) Limited
+ *
+ * noise.cpp - Noise control algorithm
+ */
+
+#include <math.h>
+
+#include "../device_status.h"
+#include "../logging.hpp"
+#include "../noise_status.h"
+
+#include "noise.hpp"
+
+using namespace RPi;
+
+#define NAME "rpi.noise"
+
+Noise::Noise(Controller *controller)
+ : Algorithm(controller), mode_factor_(1.0)
+{
+}
+
+char const *Noise::Name() const
+{
+ return NAME;
+}
+
+void Noise::SwitchMode(CameraMode const &camera_mode)
+{
+ // For example, we would expect a 2x2 binned mode to have a "noise
+ // factor" of sqrt(2x2) = 2. (can't be less than one, right?)
+ mode_factor_ = std::max(1.0, camera_mode.noise_factor);
+}
+
+void Noise::Read(boost::property_tree::ptree const &params)
+{
+ RPI_LOG(Name());
+ reference_constant_ = params.get<double>("reference_constant");
+ reference_slope_ = params.get<double>("reference_slope");
+}
+
+void Noise::Prepare(Metadata *image_metadata)
+{
+ struct DeviceStatus device_status;
+ device_status.analogue_gain = 1.0; // keep compiler calm
+ if (image_metadata->Get("device.status", device_status) == 0) {
+ // There is a slight question as to exactly how the noise
+ // profile, specifically the constant part of it, scales. For
+ // now we assume it all scales the same, and we'll revisit this
+ // if it proves substantially wrong. NOTE: we may also want to
+ // make some adjustments based on the camera mode (such as
+ // binning), if we knew how to discover it...
+ double factor = sqrt(device_status.analogue_gain) / mode_factor_;
+ struct NoiseStatus status;
+ status.noise_constant = reference_constant_ * factor;
+ status.noise_slope = reference_slope_ * factor;
+ image_metadata->Set("noise.status", status);
+ RPI_LOG(Name() << ": constant " << status.noise_constant
+ << " slope " << status.noise_slope);
+ } else
+ RPI_WARN(Name() << " no metadata");
+}
+
+// Register algorithm with the system.
+static Algorithm *Create(Controller *controller)
+{
+ return new Noise(controller);
+}
+static RegisterAlgorithm reg(NAME, &Create);