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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;
/* Limits for analogue gain values */
static constexpr double kMinAnalogueGain = 1.0;
static constexpr double kMaxAnalogueGain = 8.0;
/* Histogram constants */
static constexpr uint32_t knumHistogramBins = 256;
static constexpr double kEvGainTarget = 0.5;
Agc::Agc()
: frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
currentExposure_(0s), prevExposureValue_(0s)
{
}
int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
{
stride_ = context.configuration.grid.stride;
lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
/ configInfo.sensorInfo.pixelRate;
/* \todo replace the exposure in lines storage with time based ones. */
minExposureLines_ = context.configuration.agc.minShutterSpeed / lineDuration_;
maxExposureLines_ = context.configuration.agc.maxShutterSpeed / lineDuration_;
minAnalogueGain_ = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
maxAnalogueGain_ = std::min(context.configuration.agc.maxAnalogueGain, kMaxAnalogueGain);
/* Configure the default exposure and gain. */
context.frameContext.agc.gain = minAnalogueGain_;
context.frameContext.agc.exposure = minExposureLines_;
prevExposureValue_ = context.frameContext.agc.gain
* context.frameContext.agc.exposure
* lineDuration_;
return 0;
}
void Agc::processBrightness(const ipu3_uapi_stats_3a *stats,
const ipu3_uapi_grid_config &grid)
{
uint32_t hist[knumHistogramBins] = { 0 };
for (unsigned int cellY = 0; cellY < grid.height; cellY++) {
for (unsigned int cellX = 0; cellX < grid.width; cellX++) {
uint32_t cellPosition = cellY * stride_ + cellX;
const ipu3_uapi_awb_set_item *cell =
reinterpret_cast<const ipu3_uapi_awb_set_item *>(
&stats->awb_raw_buffer.meta_data[cellPosition]
);
if (cell->sat_ratio == 0) {
uint8_t gr = cell->Gr_avg;
uint8_t gb = cell->Gb_avg;
hist[(gr + gb) / 2]++;
}
}
}
/* 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 (filteredExposure_ == 0s) {
/* DG stands for digital gain.*/
filteredExposure_ = currentExposure_;
} else {
/*
* If we are close to the desired result, go faster to avoid making
* multiple micro-adjustments.
* \ todo: Make this customisable?
*/
if (filteredExposure_ < 1.2 * currentExposure_ &&
filteredExposure_ > 0.8 * currentExposure_)
speed = sqrt(speed);
filteredExposure_ = speed * currentExposure_ +
filteredExposure_ * (1.0 - speed);
}
LOG(IPU3Agc, Debug) << "After filtering, total_exposure " << filteredExposure_;
}
void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
{
/* 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;
lastFrame_ = frameCount_;
/* Are we correctly exposed ? */
if (std::abs(iqMean_ - kEvGainTarget * knumHistogramBins) <= 1) {
LOG(IPU3Agc, Debug) << "We are well exposed (iqMean = "
<< iqMean_ << ")";
return;
}
double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
/* extracted from Rpi::Agc::computeTargetExposure */
utils::Duration currentShutter = exposure * lineDuration_;
LOG(IPU3Agc, Debug) << "Actual total exposure " << currentShutter * analogueGain
<< " Shutter speed " << currentShutter
<< " Gain " << analogueGain
<< " Needed ev gain " << evGain;
currentExposure_ = prevExposureValue_ * evGain;
utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
utils::Duration maxTotalExposure = maxShutterSpeed * maxAnalogueGain_;
currentExposure_ = std::min(currentExposure_, maxTotalExposure);
LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
<< ", maximum is " << maxTotalExposure;
/* \todo: estimate if we need to desaturate */
filterExposure();
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 / minAnalogueGain_,
minShutterSpeed, maxShutterSpeed);
double stepGain = std::clamp(exposureValue / shutterTime,
minAnalogueGain_, maxAnalogueGain_);
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.
*
* \todo Obtain the values of the exposure time and analog gain
* that were actually used by the sensor, either from embedded
* data when available, or from the delayed controls
* infrastructure in case a slow down caused a mismatch.
*/
prevExposureValue_ = shutterTime * analogueGain;
}
void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
{
uint32_t &exposure = context.frameContext.agc.exposure;
double &analogueGain = context.frameContext.agc.gain;
processBrightness(stats, context.configuration.grid.bdsGrid);
lockExposureGain(exposure, analogueGain);
frameCount_++;
}
} /* namespace ipa::ipu3::algorithms */
} /* namespace libcamera */
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