ipa: ipu3: Add support for IPU3 AEC/AGC algorithm

Implement basic auto-exposure (AE) and auto-gain (AG) correction functions.
The functions computeTargetExposure() and computeGain() are adapted from
the Raspberry Pi AGC implementation to suit the IPU3 structures, and
filtering is added to reduce visible stepsize when there are large
exposure changes.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 202 insertions, 0 deletions

diff --git a/src/ipa/ipu3/ipu3_agc.cpp b/src/ipa/ipu3/ipu3_agc.cpp
new file mode 100644
index 00000000..ca54d89a
--- /dev/null
+++ b/src/ipa/ipu3/ipu3_agc.cpp
@@ -0,0 +1,202 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * ipu3_agc.cpp - AGC/AEC control algorithm
+ */
+
+#include "ipu3_agc.h"
+
+#include <algorithm>
+#include <cmath>
+#include <numeric>
+
+#include "libcamera/internal/log.h"
+
+#include "libipa/histogram.h"
+
+namespace libcamera {
+
+namespace ipa::ipu3 {
+
+LOG_DEFINE_CATEGORY(IPU3Agc)
+
+/* Number of frames to wait before calculating stats on minimum exposure */
+static constexpr uint32_t kInitialFrameMinAECount = 4;
+/* Number of frames to wait between new gain/exposure estimations */
+static constexpr uint32_t kFrameSkipCount = 6;
+
+/* Maximum ISO value for analogue gain */
+static constexpr uint32_t kMinISO = 100;
+static constexpr uint32_t kMaxISO = 1500;
+
+/* Maximum analogue gain value
+ * \todo grab it from a camera helper */
+static constexpr uint32_t kMinGain = kMinISO / 100;
+static constexpr uint32_t kMaxGain = kMaxISO / 100;
+
+/* \todo use calculated value based on sensor */
+static constexpr uint32_t kMinExposure = 1;
+static constexpr uint32_t kMaxExposure = 1976;
+
+/* \todo those should be get from CameraSensorInfo ! */
+/* line duration in microseconds */
+static constexpr double kLineDuration = 16.8;
+static constexpr double kMaxExposureTime = kMaxExposure * kLineDuration;
+
+/* Histogram constants */
+static constexpr uint32_t knumHistogramBins = 256;
+static constexpr double kEvGainTarget = 0.5;
+
+/* A cell is 8 bytes and contains averages for RGB values and saturation ratio */
+static constexpr uint8_t kCellSize = 8;
+
+IPU3Agc::IPU3Agc()
+	: frameCount_(0), lastFrame_(0), converged_(false),
+	  updateControls_(false), iqMean_(0.0), gamma_(1.0),
+	  prevExposure_(0.0), prevExposureNoDg_(0.0),
+	  currentExposure_(0.0), currentExposureNoDg_(0.0)
+{
+}
+
+void IPU3Agc::initialise(struct ipu3_uapi_grid_config &bdsGrid)
+{
+	aeGrid_ = bdsGrid;
+}
+
+void IPU3Agc::processBrightness(const ipu3_uapi_stats_3a *stats)
+{
+	const struct ipu3_uapi_grid_config statsAeGrid = stats->stats_4a_config.awb_config.grid;
+	Rectangle aeRegion = { statsAeGrid.x_start,
+			       statsAeGrid.y_start,
+			       static_cast<unsigned int>(statsAeGrid.x_end - statsAeGrid.x_start) + 1,
+			       static_cast<unsigned int>(statsAeGrid.y_end - statsAeGrid.y_start) + 1 };
+	Point topleft = aeRegion.topLeft();
+	int topleftX = topleft.x >> aeGrid_.block_width_log2;
+	int topleftY = topleft.y >> aeGrid_.block_height_log2;
+
+	/* Align to the grid cell width and height */
+	uint32_t startX = topleftX << aeGrid_.block_width_log2;
+	uint32_t startY = topleftY * aeGrid_.width << aeGrid_.block_width_log2;
+	uint32_t endX = (startX + (aeRegion.size().width >> aeGrid_.block_width_log2)) << aeGrid_.block_width_log2;
+	uint32_t i, j;
+	uint32_t count = 0;
+
+	uint32_t hist[knumHistogramBins] = { 0 };
+	for (j = topleftY;
+	     j < topleftY + (aeRegion.size().height >> aeGrid_.block_height_log2);
+	     j++) {
+		for (i = startX + startY; i < endX + startY; i += kCellSize) {
+			/*
+			 * The grid width (and maybe height) is not reliable.
+			 * We observed a bit shift which makes the value 160 to be 32 in the stats grid.
+			 * Use the one passed at init time.
+			 */
+			if (stats->awb_raw_buffer.meta_data[i + 4 + j * aeGrid_.width] == 0) {
+				uint8_t Gr = stats->awb_raw_buffer.meta_data[i + 0 + j * aeGrid_.width];
+				uint8_t Gb = stats->awb_raw_buffer.meta_data[i + 3 + j * aeGrid_.width];
+				hist[(Gr + Gb) / 2]++;
+				count++;
+			}
+		}
+	}
+
+	/* Limit the gamma effect for now */
+	gamma_ = 1.1;
+
+	/* Estimate the quantile mean of the top 2% of the histogram */
+	iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
+}
+
+void IPU3Agc::filterExposure()
+{
+	double speed = 0.2;
+	if (prevExposure_ == 0.0) {
+		/* DG stands for digital gain.*/
+		prevExposure_ = currentExposure_;
+		prevExposureNoDg_ = currentExposureNoDg_;
+	} else {
+		/*
+		 * If we are close to the desired result, go faster to avoid making
+		 * multiple micro-adjustments.
+		 * \ todo: Make this customisable?
+		 */
+		if (prevExposure_ < 1.2 * currentExposure_ &&
+		    prevExposure_ > 0.8 * currentExposure_)
+			speed = sqrt(speed);
+
+		prevExposure_ = speed * currentExposure_ +
+				prevExposure_ * (1.0 - speed);
+		prevExposureNoDg_ = speed * currentExposureNoDg_ +
+				prevExposureNoDg_ * (1.0 - speed);
+	}
+	/*
+	 * We can't let the no_dg exposure deviate too far below the
+	 * total exposure, as there might not be enough digital gain available
+	 * in the ISP to hide it (which will cause nasty oscillation).
+	 */
+	double fastReduceThreshold = 0.4;
+	if (prevExposureNoDg_ <
+	    prevExposure_ * fastReduceThreshold)
+		prevExposureNoDg_ = prevExposure_ * fastReduceThreshold;
+	LOG(IPU3Agc, Debug) << "After filtering, total_exposure " << prevExposure_;
+}
+
+void IPU3Agc::lockExposureGain(uint32_t &exposure, uint32_t &gain)
+{
+	updateControls_ = false;
+
+	/* Algorithm initialization should wait for first valid frames */
+	/* \todo - have a number of frames given by DelayedControls ?
+	 * - implement a function for IIR */
+	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_;
+		converged_ = true;
+	} else {
+		double newGain = kEvGainTarget * knumHistogramBins / iqMean_;
+
+		/* extracted from Rpi::Agc::computeTargetExposure */
+		double currentShutter = exposure * kLineDuration;
+		currentExposureNoDg_ = currentShutter * gain;
+		LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
+				    << " Shutter speed " << currentShutter
+				    << " Gain " << gain;
+		currentExposure_ = currentExposureNoDg_ * newGain;
+		double maxTotalExposure = kMaxExposureTime * kMaxGain;
+		currentExposure_ = std::min(currentExposure_, maxTotalExposure);
+		LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_;
+
+		/* \todo: estimate if we need to desaturate */
+		filterExposure();
+
+		double newExposure = 0.0;
+		if (currentShutter < kMaxExposureTime) {
+			exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / currentExposureNoDg_), kMinExposure, kMaxExposure);
+			newExposure = currentExposure_ / exposure;
+			gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / newExposure), kMinGain, kMaxGain);
+			updateControls_ = true;
+		} else if (currentShutter >= kMaxExposureTime) {
+			gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / currentExposureNoDg_), kMinGain, kMaxGain);
+			newExposure = currentExposure_ / gain;
+			exposure = std::clamp(static_cast<uint32_t>(exposure * currentExposure_ / newExposure), kMinExposure, kMaxExposure);
+			updateControls_ = true;
+		}
+		LOG(IPU3Agc, Debug) << "Adjust exposure " << exposure * kLineDuration << " and gain " << gain;
+	}
+	lastFrame_ = frameCount_;
+}
+
+void IPU3Agc::process(const ipu3_uapi_stats_3a *stats, uint32_t &exposure, uint32_t &gain)
+{
+	processBrightness(stats);
+	lockExposureGain(exposure, gain);
+	frameCount_++;
+}
+
+} /* namespace ipa::ipu3 */
+
+} /* namespace libcamera */