4 files changed, 50 insertions, 7 deletions
diff --git a/src/ipa/raspberrypi/controller/rpi/sharpen.cpp b/src/ipa/raspberrypi/controller/rpi/sharpen.cpp
index 4c2fdb3e..2b701db5 100644
--- a/src/ipa/raspberrypi/controller/rpi/sharpen.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/sharpen.cpp
@@ -17,7 +17,7 @@ using namespace RPi;
 #define NAME "rpi.sharpen"
 
 Sharpen::Sharpen(Controller *controller)
-	: Algorithm(controller)
+	: SharpenAlgorithm(controller), user_strength_(1.0)
 {
 }
 
@@ -42,14 +42,32 @@ void Sharpen::Read(boost::property_tree::ptree const &params)
 	limit_ = params.get<double>("limit", 1.0);
 }
 
+void Sharpen::SetStrength(double strength)
+{
+	// Note that this method is how an application sets the overall
+	// sharpening "strength". We call this the "user strength" field
+	// as there already is a strength_ field - being an internal gain
+	// parameter that gets passed to the ISP control code. Negative
+	// values are not allowed - coerce them to zero (no sharpening).
+	user_strength_ = std::max(0.0, strength);
+}
+
 void Sharpen::Prepare(Metadata *image_metadata)
 {
+	// The user_strength_ affects the algorithm's internal gain directly, but
+	// we adjust the limit and threshold less aggressively. Using a sqrt
+	// function is an arbitrary but gentle way of accomplishing this.
+	double user_strength_sqrt = sqrt(user_strength_);
 	struct SharpenStatus status;
 	// Binned modes seem to need the sharpening toned down with this
-	// pipeline.
-	status.threshold = threshold_ * mode_factor_;
-	status.strength = strength_ / mode_factor_;
-	status.limit = limit_ / mode_factor_;
+	// pipeline, thus we use the mode_factor here. Also avoid
+	// divide-by-zero with the user_strength_sqrt.
+	status.threshold = threshold_ * mode_factor_ /
+			   std::max(0.01, user_strength_sqrt);
+	status.strength = strength_ / mode_factor_ * user_strength_;
+	status.limit = limit_ / mode_factor_ * user_strength_sqrt;
+	// Finally, report any application-supplied parameters that were used.
+	status.user_strength = user_strength_;
 	image_metadata->Set("sharpen.status", status);
 }
 
diff --git a/src/ipa/raspberrypi/controller/rpi/sharpen.hpp b/src/ipa/raspberrypi/controller/rpi/sharpen.hpp
index a3bf899d..568521b9 100644
--- a/src/ipa/raspberrypi/controller/rpi/sharpen.hpp
+++ b/src/ipa/raspberrypi/controller/rpi/sharpen.hpp
@@ -6,20 +6,21 @@
  */
 #pragma once
 
-#include "../algorithm.hpp"
+#include "../sharpen_algorithm.hpp"
 #include "../sharpen_status.h"
 
 // This is our implementation of the "sharpen algorithm".
 
 namespace RPi {
 
-class Sharpen : public Algorithm
+class Sharpen : public SharpenAlgorithm
 {
 public:
 	Sharpen(Controller *controller);
 	char const *Name() const override;
 	void SwitchMode(CameraMode const &camera_mode, Metadata *metadata) override;
 	void Read(boost::property_tree::ptree const &params) override;
+	void SetStrength(double strength) override;
 	void Prepare(Metadata *image_metadata) override;
 
 private:
@@ -27,6 +28,7 @@ private:
 	double strength_;
 	double limit_;
 	double mode_factor_;
+	double user_strength_;
 };
 
 } // namespace RPi
diff --git a/src/ipa/raspberrypi/controller/sharpen_algorithm.hpp b/src/ipa/raspberrypi/controller/sharpen_algorithm.hpp
new file mode 100644
index 00000000..3b27a745
--- /dev/null
+++ b/src/ipa/raspberrypi/controller/sharpen_algorithm.hpp
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2020, Raspberry Pi (Trading) Limited
+ *
+ * sharpen_algorithm.hpp - sharpness control algorithm interface
+ */
+#pragma once
+
+#include "algorithm.hpp"
+
+namespace RPi {
+
+class SharpenAlgorithm : public Algorithm
+{
+public:
+	SharpenAlgorithm(Controller *controller) : Algorithm(controller) {}
+	// A sharpness control algorithm must provide the following:
+	virtual void SetStrength(double strength) = 0;
+};
+
+} // namespace RPi
diff --git a/src/ipa/raspberrypi/controller/sharpen_status.h b/src/ipa/raspberrypi/controller/sharpen_status.h
index 6de80f40..7501b191 100644
--- a/src/ipa/raspberrypi/controller/sharpen_status.h
+++ b/src/ipa/raspberrypi/controller/sharpen_status.h
@@ -19,6 +19,8 @@ struct SharpenStatus {
 	double strength;
 	// upper limit of the allowed sharpening response
 	double limit;
+	// The sharpening strength requested by the user or application.
+	double user_strength;
 };
 
 #ifdef __cplusplus