ipa: rkisp1: agc: Fix metering modes

The weights for a given metering mode are applied to the histogram data
inside the histogram statistics block. The AE statistics do not contain
any weights. Therefore the weights are honored when AgcMeanLuminance
calculates the upper or lower constraints, but ignored in the
calculation of the frame luminance. Fix that by manually applying the
weights in the luminance calculation.

Fixes: 4c5152843a ("ipa: rkisp1: Derive rkisp1::algorithms::Agc from AgcMeanLuminance")
Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/rkisp1/algorithms/agc.cpp

@@ -439,15 +439,20 @@ void Agc::fillMetadata(IPAContext &context, IPAFrameContext &frameContext,
  */
 double Agc::estimateLuminance(double gain) const
 {
+	ASSERT(expMeans_.size() == weights_.size());
 	double ySum = 0.0;
+	double wSum = 0.0;
 
 	/* Sum the averages, saturated to 255. */
-	for (uint8_t expMean : expMeans_)
-		ySum += std::min(expMean * gain, 255.0);
+	for (unsigned i = 0; i < expMeans_.size(); i++) {
+		double w = weights_[i];
+		ySum += std::min(expMeans_[i] * gain, 255.0) * w;
+		wSum += w;
+	}
 
 	/* \todo Weight with the AWB gains */
 
-	return ySum / expMeans_.size() / 255;
+	return ySum / wSum / 255;
 }
 
 /**
@@ -515,6 +520,8 @@ void Agc::process(IPAContext &context, [[maybe_unused]] const uint32_t frame,
 	Histogram hist({ params->hist.hist_bins, context.hw->numHistogramBins },
 		       [](uint32_t x) { return x >> 4; });
 	expMeans_ = { params->ae.exp_mean, context.hw->numAeCells };
+	std::vector<uint8_t> &modeWeights = meteringModes_.at(frameContext.agc.meteringMode);
+	weights_ = { modeWeights.data(), modeWeights.size() };
 
 	/*
 	 * Set the AGC limits using the fixed exposure time and/or gain in

src/ipa/rkisp1/algorithms/agc.h

@@ -55,6 +55,7 @@ private:
 				  utils::Duration frameDuration);
 
 	Span<const uint8_t> expMeans_;
+	Span<const uint8_t> weights_;
 
 	std::map<int32_t, std::vector<uint8_t>> meteringModes_;
 };