[libcamera-devel] [PATCH v2 08/14] ipa: ipu3: agc: Update previous exposure value

[Jean-Michel Hautbois]

Previously, the exposure value was calculated based on the estimated
shutter time and gain applied. Now that we have the real values for the
current frame, use those before estimating the next one and rename the
variable accordingly.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/agc.cpp | 32 +++++++++++---------------------
 src/ipa/ipu3/algorithms/agc.h   |  2 +-
 2 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index ee37a9d5..38667e61 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -73,7 +73,7 @@ static constexpr uint32_t kMaxLuminance = 255;
 Agc::Agc()
 	: frameCount_(0), iqMean_(0.0), lineDuration_(0s), minExposureLines_(0),
 	  maxExposureLines_(0), filteredExposure_(0s), currentExposure_(0s),
-	  prevExposureValue_(0s)
+	  effectiveExposureValue_(0s)
 {
 }
 
@@ -104,9 +104,9 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
 	context.frameContext.agc.gain = minAnalogueGain_;
 	context.frameContext.agc.exposure = minExposureLines_;
 
-	prevExposureValue_ = context.frameContext.agc.gain
-			   * context.frameContext.agc.exposure
-			   * lineDuration_;
+	effectiveExposureValue_ = context.frameContext.agc.gain
+				* context.frameContext.agc.exposure
+				* lineDuration_;
 
 	return 0;
 }
@@ -201,16 +201,16 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain, double curre
 	 */
 	double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
 
-	if (std::abs(evGain - 1.0) < 0.01) {
-		LOG(IPU3Agc, Debug) << "We are well exposed (iqMean = "
-				    << iqMean_ << ")";
-		return;
-	}
-
 	/* extracted from Rpi::Agc::computeTargetExposure */
 
 	/* Calculate the shutter time in seconds */
 	utils::Duration currentShutter = exposure * lineDuration_;
+	/*
+	 * Update the exposure value for the next computation using the values
+	 * of exposure and gain really used by the sensor.
+	 */
+	effectiveExposureValue_ = currentShutter * analogueGain;
+
 	LOG(IPU3Agc, Debug) << "Actual total exposure " << currentShutter * analogueGain
 			    << " Shutter speed " << currentShutter
 			    << " Gain " << analogueGain
@@ -228,7 +228,7 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain, double curre
 	 * Calculate the current exposure value for the scene as the latest
 	 * exposure value applied multiplied by the new estimated gain.
 	 */
-	currentExposure_ = prevExposureValue_ * evGain;
+	currentExposure_ = effectiveExposureValue_ * evGain;
 	utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
 	utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
 
@@ -259,16 +259,6 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain, double curre
 
 	exposure = shutterTime / lineDuration_;
 	analogueGain = stepGain;
-
-	/*
-	 * Update the exposure value for the next process call.
-	 *
-	 * \todo Obtain the values of the exposure time and analog gain
-	 * that were actually used by the sensor, either from embedded
-	 * data when available, or from the delayed controls
-	 * infrastructure in case a slow down caused a mismatch.
-	 */
-	prevExposureValue_ = shutterTime * analogueGain;
 }
 
 /**
diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
index 0a9152a9..51174639 100644
--- a/src/ipa/ipu3/algorithms/agc.h
+++ b/src/ipa/ipu3/algorithms/agc.h
@@ -54,7 +54,7 @@ private:
 
 	utils::Duration filteredExposure_;
 	utils::Duration currentExposure_;
-	utils::Duration prevExposureValue_;
+	utils::Duration effectiveExposureValue_;
 
 	uint32_t stride_;
 };
-- 
2.32.0