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libcamera: src: ipa: raspberrypi: agc: Improve gain update calculation for partly saturated images

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When parts of an image saturate then the image brightness no longer
increases linearly with increased exposure/gain. Having calculated a
linear gain value it's better then to try it, allowing for saturating
regions, and if necessary increase the gain some more. We repeat this
several times.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
David Plowman 2020-11-23 07:38:03 +00:00 • committed by Kieran Bingham
parent 393f05a9a8
commit 7de5506c30
1 changed files with 24 additions and 10 deletions
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34
src/ipa/raspberrypi/controller/rpi/agc.cpp
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@ -419,17 +419,21 @@ void Agc::fetchAwbStatus(Metadata *image_metadata)
}
static double compute_initial_Y(bcm2835_isp_stats *stats, AwbStatus const &awb,
double weights[])
double weights[], double gain)
{
bcm2835_isp_stats_region *regions = stats->agc_stats;
// Note how the calculation below means that equal weights give you
// "average" metering (i.e. all pixels equally important).
double R_sum = 0, G_sum = 0, B_sum = 0, pixel_sum = 0;
for (int i = 0; i < AGC_STATS_SIZE; i++) {
R_sum += regions[i].r_sum * weights[i];
G_sum += regions[i].g_sum * weights[i];
B_sum += regions[i].b_sum * weights[i];
pixel_sum += regions[i].counted * weights[i];
double counted = regions[i].counted;
double r_sum = std::min(regions[i].r_sum * gain, ((1 << PIPELINE_BITS) - 1) * counted);
double g_sum = std::min(regions[i].g_sum * gain, ((1 << PIPELINE_BITS) - 1) * counted);
double b_sum = std::min(regions[i].b_sum * gain, ((1 << PIPELINE_BITS) - 1) * counted);
R_sum += r_sum * weights[i];
G_sum += g_sum * weights[i];
B_sum += b_sum * weights[i];
pixel_sum += counted * weights[i];
}
if (pixel_sum == 0.0) {
LOG(RPiAgc, Warning) << "compute_initial_Y: pixel_sum is zero";
@ -473,11 +477,21 @@ void Agc::computeGain(bcm2835_isp_stats *statistics, Metadata *image_metadata,
target_Y =
config_.Y_target.Eval(config_.Y_target.Domain().Clip(lux.lux));
target_Y = std::min(EV_GAIN_Y_TARGET_LIMIT, target_Y * ev_gain);
double initial_Y = compute_initial_Y(statistics, awb_,
metering_mode_->weights);
gain = std::min(10.0, target_Y / (initial_Y + .001));
LOG(RPiAgc, Debug) << "Initially Y " << initial_Y << " target " << target_Y
<< " gives gain " << gain;
// Do this calculation a few times as brightness increase can be
// non-linear when there are saturated regions.
gain = 1.0;
for (int i = 0; i < 8; i++) {
double initial_Y = compute_initial_Y(statistics, awb_,
metering_mode_->weights, gain);
double extra_gain = std::min(10.0, target_Y / (initial_Y + .001));
gain *= extra_gain;
LOG(RPiAgc, Debug) << "Initial Y " << initial_Y << " target " << target_Y
<< " gives gain " << gain;
if (extra_gain < 1.01) // close enough
break;
}
for (auto &c : *constraint_mode_) {
double new_target_Y;
double new_gain =