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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2024, Red Hat Inc.
*
* Exposure and gain
*/
#include "agc.h"
#include <stdint.h>
#include <libcamera/base/log.h>
namespace libcamera {
LOG_DEFINE_CATEGORY(IPASoftExposure)
namespace ipa::soft::algorithms {
/*
* The number of bins to use for the optimal exposure calculations.
*/
static constexpr unsigned int kExposureBinsCount = 5;
/*
* The exposure is optimal when the mean sample value of the histogram is
* in the middle of the range.
*/
static constexpr float kExposureOptimal = kExposureBinsCount / 2.0;
/*
* The below value implements the hysteresis for the exposure adjustment.
* It is small enough to have the exposure close to the optimal, and is big
* enough to prevent the exposure from wobbling around the optimal value.
*/
static constexpr float kExposureSatisfactory = 0.2;
Agc::Agc()
{
}
void Agc::updateExposure(IPAContext &context, double exposureMSV)
{
/*
* kExpDenominator of 10 gives ~10% increment/decrement;
* kExpDenominator of 5 - about ~20%
*/
static constexpr uint8_t kExpDenominator = 10;
static constexpr uint8_t kExpNumeratorUp = kExpDenominator + 1;
static constexpr uint8_t kExpNumeratorDown = kExpDenominator - 1;
double next;
int32_t &exposure = context.activeState.agc.exposure;
double &again = context.activeState.agc.again;
if (exposureMSV < kExposureOptimal - kExposureSatisfactory) {
next = exposure * kExpNumeratorUp / kExpDenominator;
if (next - exposure < 1)
exposure += 1;
else
exposure = next;
if (exposure >= context.configuration.agc.exposureMax) {
next = again * kExpNumeratorUp / kExpDenominator;
if (next - again < context.configuration.agc.againMinStep)
again += context.configuration.agc.againMinStep;
else
again = next;
}
}
if (exposureMSV > kExposureOptimal + kExposureSatisfactory) {
if (exposure == context.configuration.agc.exposureMax &&
again > context.configuration.agc.againMin) {
next = again * kExpNumeratorDown / kExpDenominator;
if (again - next < context.configuration.agc.againMinStep)
again -= context.configuration.agc.againMinStep;
else
again = next;
} else {
next = exposure * kExpNumeratorDown / kExpDenominator;
if (exposure - next < 1)
exposure -= 1;
else
exposure = next;
}
}
exposure = std::clamp(exposure, context.configuration.agc.exposureMin,
context.configuration.agc.exposureMax);
again = std::clamp(again, context.configuration.agc.againMin,
context.configuration.agc.againMax);
LOG(IPASoftExposure, Debug)
<< "exposureMSV " << exposureMSV
<< " exp " << exposure << " again " << again;
}
void Agc::process(IPAContext &context,
[[maybe_unused]] const uint32_t frame,
[[maybe_unused]] IPAFrameContext &frameContext,
const SwIspStats *stats,
[[maybe_unused]] ControlList &metadata)
{
/*
* Calculate Mean Sample Value (MSV) according to formula from:
* https://www.araa.asn.au/acra/acra2007/papers/paper84final.pdf
*/
const auto &histogram = stats->yHistogram;
const unsigned int blackLevelHistIdx =
context.activeState.blc.level / (256 / SwIspStats::kYHistogramSize);
const unsigned int histogramSize =
SwIspStats::kYHistogramSize - blackLevelHistIdx;
const unsigned int yHistValsPerBin = histogramSize / kExposureBinsCount;
const unsigned int yHistValsPerBinMod =
histogramSize / (histogramSize % kExposureBinsCount + 1);
int exposureBins[kExposureBinsCount] = {};
unsigned int denom = 0;
unsigned int num = 0;
for (unsigned int i = 0; i < histogramSize; i++) {
unsigned int idx = (i - (i / yHistValsPerBinMod)) / yHistValsPerBin;
exposureBins[idx] += histogram[blackLevelHistIdx + i];
}
for (unsigned int i = 0; i < kExposureBinsCount; i++) {
LOG(IPASoftExposure, Debug) << i << ": " << exposureBins[i];
denom += exposureBins[i];
num += exposureBins[i] * (i + 1);
}
float exposureMSV = (denom == 0 ? 0 : static_cast<float>(num) / denom);
updateExposure(context, exposureMSV);
}
REGISTER_IPA_ALGORITHM(Agc, "Agc")
} /* namespace ipa::soft::algorithms */
} /* namespace libcamera */
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