[libcamera-devel] [PATCH 2/3] libcamera: ipa: raspberrypi: ALSC: Resample luminance table

[David Plowman]

This fixes a bug where the luminance correction table was not being
resampled according to the camera mode, in the same way as the colour
tables. This could be noticeable if any camera modes crop
aggressively.

This resampling can be done "up front" in the SwitchMode, as we have
only a single fixed luminance table. In order to protect the
recalculation of the table from the asynchronous thread (which reads
it) I've elected to wait for that thread to go idle (though I doubt it
would have mattered much). As a by-product of stopping the thread, it
no longer needs its own copy of the camera mode (async_camera_mode_).

Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
---
 src/ipa/raspberrypi/controller/rpi/alsc.cpp | 39 ++++++++++++++-------
 src/ipa/raspberrypi/controller/rpi/alsc.hpp |  3 +-
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/src/ipa/raspberrypi/controller/rpi/alsc.cpp b/src/ipa/raspberrypi/controller/rpi/alsc.cpp
index 76e2f04..8f7720b 100644
--- a/src/ipa/raspberrypi/controller/rpi/alsc.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/alsc.cpp
@@ -173,19 +173,34 @@ void Alsc::Initialise()
 		lambda_r_[i] = lambda_b_[i] = 1.0;
 }
 
+void Alsc::waitForAysncThread()
+{
+	std::unique_lock<std::mutex> lock(mutex_);
+	if (async_started_) {
+		sync_signal_.wait(lock, [&] {
+			return async_finished_;
+		});
+		async_started_ = false;
+		async_finished_ = false;
+	}
+}
+
 void Alsc::SwitchMode(CameraMode const &camera_mode, Metadata *metadata)
 {
 	(void)metadata;
 
+	// Ensure the other thread isn't running while we do this.
+	waitForAysncThread();
+
 	// There's a bit of a question what we should do if the "crop" of the
-	// camera mode has changed.  Any calculation currently in flight would
-	// not be useful to the new mode, so arguably we should abort it, and
-	// generate a new table (like the "first_time" code already here).  When
-	// the crop doesn't change, we can presumably just leave things
-	// alone. For now, I think we'll just wait and see. When the crop does
-	// change, any effects should be transient, and if they're not transient
-	// enough, we'll revisit the question then.
+	// camera mode has changed. Should we effectively reset the algorithm
+	// and start over?
 	camera_mode_ = camera_mode;
+
+	// We must resample the luminance table like we do the others, but it's
+	// fixed so we can simply do it up front here.
+	resample_cal_table(config_.luminance_lut, camera_mode_, luminance_table_);
+
 	if (first_time_) {
 		// On the first time, arrange for something sensible in the
 		// initial tables. Construct the tables for some default colour
@@ -201,7 +216,7 @@ void Alsc::SwitchMode(CameraMode const &camera_mode, Metadata *metadata)
 		compensate_lambdas_for_cal(cal_table_b, lambda_b_,
 					   async_lambda_b_);
 		add_luminance_to_tables(sync_results_, async_lambda_r_, 1.0,
-					async_lambda_b_, config_.luminance_lut,
+					async_lambda_b_, luminance_table_,
 					config_.luminance_strength);
 		memcpy(prev_sync_results_, sync_results_,
 		       sizeof(prev_sync_results_));
@@ -266,8 +281,6 @@ void Alsc::restartAsync(StatisticsPtr &stats, Metadata *image_metadata)
 	}
 	copy_stats(statistics_, stats, alsc_status);
 	frame_phase_ = 0;
-	// copy the camera mode so it won't change during the calculations
-	async_camera_mode_ = camera_mode_;
 	async_start_ = true;
 	async_started_ = true;
 	async_signal_.notify_one();
@@ -670,9 +683,9 @@ void Alsc::doAlsc()
 	// Fetch the new calibrations (if any) for this CT. Resample them in
 	// case the camera mode is not full-frame.
 	get_cal_table(ct_, config_.calibrations_Cr, cal_table_tmp);
-	resample_cal_table(cal_table_tmp, async_camera_mode_, cal_table_r);
+	resample_cal_table(cal_table_tmp, camera_mode_, cal_table_r);
 	get_cal_table(ct_, config_.calibrations_Cb, cal_table_tmp);
-	resample_cal_table(cal_table_tmp, async_camera_mode_, cal_table_b);
+	resample_cal_table(cal_table_tmp, camera_mode_, cal_table_b);
 	// You could print out the cal tables for this image here, if you're
 	// tuning the algorithm...
 	(void)print_cal_table;
@@ -695,7 +708,7 @@ void Alsc::doAlsc()
 	compensate_lambdas_for_cal(cal_table_b, lambda_b_, async_lambda_b_);
 	// Fold in the luminance table at the appropriate strength.
 	add_luminance_to_tables(async_results_, async_lambda_r_, 1.0,
-				async_lambda_b_, config_.luminance_lut,
+				async_lambda_b_, luminance_table_,
 				config_.luminance_strength);
 }
 
diff --git a/src/ipa/raspberrypi/controller/rpi/alsc.hpp b/src/ipa/raspberrypi/controller/rpi/alsc.hpp
index e895913..95572af 100644
--- a/src/ipa/raspberrypi/controller/rpi/alsc.hpp
+++ b/src/ipa/raspberrypi/controller/rpi/alsc.hpp
@@ -60,10 +60,10 @@ private:
 	AlscConfig config_;
 	bool first_time_;
 	CameraMode camera_mode_;
+	double luminance_table_[ALSC_CELLS_X * ALSC_CELLS_Y];
 	std::thread async_thread_;
 	void asyncFunc(); // asynchronous thread function
 	std::mutex mutex_;
-	CameraMode async_camera_mode_;
 	// condvar for async thread to wait on
 	std::condition_variable async_signal_;
 	// condvar for synchronous thread to wait on
@@ -86,6 +86,7 @@ private:
 	int frame_count2_;
 	double sync_results_[3][ALSC_CELLS_Y][ALSC_CELLS_X];
 	double prev_sync_results_[3][ALSC_CELLS_Y][ALSC_CELLS_X];
+	void waitForAysncThread();
 	// The following are for the asynchronous thread to use, though the main
 	// thread can set/reset them if the async thread is known to be idle:
 	void restartAsync(StatisticsPtr &stats, Metadata *image_metadata);
-- 
2.20.1