[libcamera-devel] [PATCH 08/13] ipa: ipu3: agc: Simplify division of exposure/gain

[Jean-Michel Hautbois]

We are not using the filtered result from filterExposure() and we make
complex assumptions when dividing the exposure and analogue gain values.

Use the same mechanism as in RPiController::Agc::divideUpExposure() with
the fixed limits defined previously. This simplifies the understanding,
and corrects a bug in the analogue gain calculus.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/agc.cpp | 37 ++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index e58a8a8d..3ec1c60c 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -153,17 +153,34 @@ void Agc::lockExposureGain(uint32_t &exposure, double &gain)
 		/* \todo: estimate if we need to desaturate */
 		filterExposure();
 
-		Duration newExposure = 0.0s;
-		if (currentShutter < kMaxShutterSpeed) {
-			exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / currentExposureNoDg_), minExposureLines_, maxExposureLines_);
-			newExposure = currentExposure_ / exposure;
-			gain = std::clamp(static_cast<double>(gain * currentExposure_ / newExposure), kMinGain, kMaxGain);
-		} else if (currentShutter >= kMaxShutterSpeed) {
-			gain = std::clamp(static_cast<double>(gain * currentExposure_ / currentExposureNoDg_), kMinGain, kMaxGain);
-			newExposure = currentExposure_ / gain;
-			exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / newExposure), minExposureLines_, maxExposureLines_);
+		Duration exposureValue = filteredExposure_;
+		Duration shutterTime = kMinShutterSpeed;
+		double stepGain = kMinGain;
+
+		if (shutterTime * stepGain < exposureValue) {
+			Duration maxShutterMinGain = kMaxShutterSpeed * stepGain;
+			if (maxShutterMinGain >= exposureValue) {
+				LOG(IPU3Agc, Debug) << "Setting shutterTime to " << shutterTime;
+				shutterTime = exposureValue / stepGain;
+			} else {
+				shutterTime = kMaxShutterSpeed;
+			}
+
+			Duration maxGainShutter = kMaxGain * shutterTime;
+			if (maxGainShutter >= exposureValue) {
+				stepGain = exposureValue / shutterTime;
+				LOG(IPU3Agc, Debug) << "Setting analogue gain to " << stepGain;
+			} else {
+				stepGain = kMaxGain;
+			}
 		}
-		LOG(IPU3Agc, Debug) << "Adjust exposure " << exposure * lineDuration_ << " and gain " << gain;
+
+		LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
+				<< shutterTime << " and "
+				<< stepGain;
+
+		exposure = shutterTime / lineDuration_;
+		gain = stepGain;
 	}
 	lastFrame_ = frameCount_;
 }
-- 
2.30.2