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+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * ipu3_agc.cpp - AGC/AEC control algorithm
+ */
+
+#include "agc.h"
+
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+
+#include <libcamera/base/log.h>
+
+#include <libcamera/ipa/core_ipa_interface.h>
+
+#include "libipa/histogram.h"
+
+namespace libcamera {
+
+using namespace std::literals::chrono_literals;
+
+namespace ipa::ipu3::algorithms {
+
+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;
+
+/* 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;
+
+Agc::Agc()
+ : frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
+ maxExposureTime_(0s), prevExposure_(0s), prevExposureNoDg_(0s),
+ currentExposure_(0s), currentExposureNoDg_(0s)
+{
+}
+
+int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
+{
+ aeGrid_ = context.configuration.grid.bdsGrid;
+
+ lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
+ / configInfo.sensorInfo.pixelRate;
+ maxExposureTime_ = kMaxExposure * lineDuration_;
+
+ return 0;
+}
+
+void Agc::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++;
+ }
+ }
+ }
+
+ /* Estimate the quantile mean of the top 2% of the histogram */
+ iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
+}
+
+void Agc::filterExposure()
+{
+ double speed = 0.2;
+ if (prevExposure_ == 0s) {
+ /* 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 Agc::lockExposureGain(uint32_t &exposure, double &gain)
+{
+ /* 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_;
+ } else {
+ double newGain = kEvGainTarget * knumHistogramBins / iqMean_;
+
+ /* extracted from Rpi::Agc::computeTargetExposure */
+ libcamera::utils::Duration currentShutter = exposure * lineDuration_;
+ currentExposureNoDg_ = currentShutter * gain;
+ LOG(IPU3Agc, Debug) << "Actual total exposure " << currentExposureNoDg_
+ << " Shutter speed " << currentShutter
+ << " Gain " << gain;
+ currentExposure_ = currentExposureNoDg_ * newGain;
+ libcamera::utils::Duration maxTotalExposure = maxExposureTime_ * kMaxGain;
+ currentExposure_ = std::min(currentExposure_, maxTotalExposure);
+ LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_;
+
+ /* \todo: estimate if we need to desaturate */
+ filterExposure();
+
+ libcamera::utils::Duration newExposure = 0.0s;
+ if (currentShutter < maxExposureTime_) {
+ 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);
+ } else if (currentShutter >= maxExposureTime_) {
+ 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);
+ }
+ LOG(IPU3Agc, Debug) << "Adjust exposure " << exposure * lineDuration_ << " and gain " << gain;
+ }
+ lastFrame_ = frameCount_;
+}
+
+void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
+{
+ uint32_t &exposure = context.frameContext.agc.exposure;
+ double &gain = context.frameContext.agc.gain;
+ processBrightness(stats);
+ lockExposureGain(exposure, gain);
+ frameCount_++;
+}
+
+} /* namespace ipa::ipu3::algorithms */
+
+} /* namespace libcamera */