[libcamera-devel] [PATCH v2 08/13] ipa: ipu3: agc: Simplify division of exposure/gain
Jean-Michel Hautbois
jeanmichel.hautbois at ideasonboard.com
Wed Oct 20 17:46:02 CEST 2021
Until now, the algorithm makes complex assumptions when dividing the
exposure and analogue gain values. Instead, use a simpler clamping of
the shutter speed first, and then of the analogue gain, based on the
limits configured.
While at it, correct a bug which makes the algorithm not use the
filtered result from filterExposure().
Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
src/ipa/ipu3/algorithms/agc.cpp | 36 +++++++++++++++++----------------
1 file changed, 19 insertions(+), 17 deletions(-)
diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index 1bae1eb9..84e41834 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -146,7 +146,9 @@ void Agc::lockExposureGain(uint32_t &exposure, double &gain)
<< " Gain " << gain;
currentExposure_ = currentExposureNoDg_ * newGain;
+ 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_
@@ -155,23 +157,23 @@ void Agc::lockExposureGain(uint32_t &exposure, double &gain)
/* \todo: estimate if we need to desaturate */
filterExposure();
- utils::Duration newExposure = 0.0s;
- if (currentShutter < maxShutterSpeed) {
- exposure = std::clamp<uint32_t>(exposure * currentExposure_ / currentExposureNoDg_,
- minExposureLines_,
- maxExposureLines_);
- newExposure = currentExposure_ / exposure;
- gain = std::clamp(gain * currentExposure_ / newExposure,
- kMinGain, kMaxGain);
- } else if (currentShutter >= maxShutterSpeed) {
- gain = std::clamp(gain * currentExposure_ / currentExposureNoDg_,
- kMinGain, kMaxGain);
- newExposure = currentExposure_ / gain;
- exposure = std::clamp<uint32_t>(exposure * currentExposure_ / newExposure,
- minExposureLines_,
- maxExposureLines_);
- }
- LOG(IPU3Agc, Debug) << "Adjust exposure " << exposure * lineDuration_ << " and gain " << gain;
+ 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_;
+ gain = stepGain;
}
lastFrame_ = frameCount_;
}
--
2.32.0
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