[libcamera-devel] [PATCH v2 11/13] ipa: ipu3: agc: Remove condition on exposure correction

[Jean-Michel Hautbois]

Until now, we can't know when the exposure and gains applied in the
IPAIPU3::setControls() are really applied (it can be several frames). We
don't want to use the values calculated as if they are already applied,
and this is done by testing the frame number.

When the exposure is estimated, we verify if it changed enough for
exposure and gain to be updated.

There is no need for that because we are now filtering the value with
the previous one correctly, so if the change is very small the exposure
and analogue gain my evolve a bit but it should not be visible to the
user.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/agc.cpp | 78 ++++++++++++++++-----------------
 1 file changed, 37 insertions(+), 41 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index 19f3a420..0417dc99 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -138,53 +138,49 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
 	if ((frameCount_ < kInitialFrameMinAECount) || (frameCount_ - lastFrame_ < kFrameSkipCount))
 		return;
 
-	/* Are we correctly exposed ? */
-	if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1) {
-		LOG(IPU3Agc, Debug) << "!!! Good exposure with iqMean = " << iqMean_;
-	} else {
-		double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
+	double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
 
-		/* extracted from Rpi::Agc::computeTargetExposure */
-		utils::Duration currentShutter = exposure * lineDuration_;
-		currentExposureNoDg_ = currentShutter * analogueGain;
-		LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
-				    << " Shutter speed " << currentShutter
-				    << " Gain " << analogueGain
-				    << " Needed ev gain " << evGain;
+	/* extracted from Rpi::Agc::computeTargetExposure */
+	utils::Duration currentShutter = exposure * lineDuration_;
+	currentExposureNoDg_ = currentShutter * analogueGain;
+	LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
+			    << " Shutter speed " << currentShutter
+			    << " Gain " << analogueGain
+			    << " Needed ev gain " << evGain;
 
-		currentExposure_ = prevExposureValue_ * evGain;
-		utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
-		utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
+	currentExposure_ = prevExposureValue_ * evGain;
+	utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
+	utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
 
-		utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
-		currentExposure_ = std::min(currentExposure_, maxTotalExposure);
-		LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
-				    << ", maximum is " << maxTotalExposure;
+	utils::Duration maxTotalExposure = maxShutterSpeed * kMaxGain;
+	currentExposure_ = std::min(currentExposure_, maxTotalExposure);
+	LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
+			    << ", maximum is " << maxTotalExposure;
 
-		/* \todo: estimate if we need to desaturate */
-		filterExposure();
+	/* \todo: estimate if we need to desaturate */
+	filterExposure();
 
-		utils::Duration exposureValue = filteredExposure_;
-		utils::Duration shutterTime = minShutterSpeed;
+	utils::Duration exposureValue = filteredExposure_;
+	utils::Duration shutterTime = minShutterSpeed;
+
+	/*
+	* Push the shutter time up to the maximum first, and only then
+	* increase the gain.
+	*/
+	shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
+						  minShutterSpeed, maxShutterSpeed);
+	double stepGain = std::clamp(exposureValue / shutterTime,
+				     kMinGain, kMaxGain);
+	LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
+			    << shutterTime << " and "
+			    << stepGain;
+
+	exposure = shutterTime / lineDuration_;
+	analogueGain = stepGain;
+
+	/* Update the exposure value for the next process call */
+	prevExposureValue_ = shutterTime * analogueGain;
 
-		/*
-		 * Push the shutter time up to the maximum first, and only then
-		 * increase the gain.
-		 */
-		shutterTime = std::clamp<utils::Duration>(exposureValue / kMinGain,
-							  minShutterSpeed, maxShutterSpeed);
-		double stepGain = std::clamp(exposureValue / shutterTime,
-					     kMinGain, kMaxGain);
-		LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
-				    << shutterTime << " and "
-				    << stepGain;
-
-		exposure = shutterTime / lineDuration_;
-		analogueGain = stepGain;
-
-		/* Update the exposure value for the next process call */
-		prevExposureValue_ = shutterTime * analogueGain;
-	}
 	lastFrame_ = frameCount_;
 }
 
-- 
2.32.0