1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
|
/* 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;
/*
* This 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, IPAFrameContext &frameContext, 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 = frameContext.sensor.exposure;
double &again = frameContext.sensor.gain;
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, frameContext, exposureMSV);
}
REGISTER_IPA_ALGORITHM(Agc, "Agc")
} /* namespace ipa::soft::algorithms */
} /* namespace libcamera */
|
