@@ -70,7 +70,7 @@ static constexpr uint32_t kNumStartupFrames = 10;
static constexpr double kRelativeLuminanceTarget = 0.16;
Agc::Agc()
- : frameCount_(0), iqMean_(0.0), lineDuration_(0s), minShutterSpeed_(0s),
+ : frameCount_(0), lineDuration_(0s), minShutterSpeed_(0s),
maxShutterSpeed_(0s), filteredExposure_(0s), currentExposure_(0s)
{
}
@@ -108,9 +108,10 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
* \brief Estimate the mean value of the top 2% of the histogram
* \param[in] stats The statistics computed by the ImgU
* \param[in] grid The grid used to store the statistics in the IPU3
+ * \return The mean value of the top 2% of the histogram
*/
-void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
- const ipu3_uapi_grid_config &grid)
+double Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
+ const ipu3_uapi_grid_config &grid) const
{
/* Initialise the histogram array */
uint32_t hist[knumHistogramBins] = { 0 };
@@ -135,8 +136,8 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
}
}
- /* Estimate the quantile mean of the top 2% of the histogram */
- iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
+ /* Estimate the quantile mean of the top 2% of the histogram. */
+ return Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
}
/**
@@ -174,28 +175,22 @@ void Agc::filterExposure()
* \brief Estimate the new exposure and gain values
* \param[inout] frameContext The shared IPA frame Context
* \param[in] yGain The gain calculated based on the relative luminance target
+ * \param[in] iqMeanGain The gain calculated based on the relative luminance target
*/
-void Agc::computeExposure(IPAFrameContext &frameContext, double yGain)
+void Agc::computeExposure(IPAFrameContext &frameContext, double yGain,
+ double iqMeanGain)
{
/* Get the effective exposure and gain applied on the sensor. */
uint32_t exposure = frameContext.sensor.exposure;
double analogueGain = frameContext.sensor.gain;
- /*
- * Estimate the gain needed to have the proportion of pixels in a given
- * desired range. iqMean_ returns the mean value of the top 2% of the
- * cumulative histogram, and we want it to be as close as possible to a
- * configured target.
- */
- double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
-
- if (evGain < yGain)
- evGain = yGain;
+ /* Use the highest of the two gain estimates. */
+ double evGain = std::max(yGain, iqMeanGain);
/* Consider within 1% of the target as correctly exposed */
if (std::abs(evGain - 1.0) < 0.01)
- LOG(IPU3Agc, Debug) << "We are well exposed (iqMean = "
- << iqMean_ << ")";
+ LOG(IPU3Agc, Debug) << "We are well exposed (evGain = "
+ << evGain << ")";
/* extracted from Rpi::Agc::computeTargetExposure */
@@ -308,15 +303,25 @@ double Agc::estimateLuminance(IPAFrameContext &frameContext,
*/
void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
{
- measureBrightness(stats, context.configuration.grid.bdsGrid);
+ /*
+ * Estimate the gain needed to have the proportion of pixels in a given
+ * desired range. iqMean is the mean value of the top 2% of the
+ * cumulative histogram, and we want it to be as close as possible to a
+ * configured target.
+ */
+ double iqMean = measureBrightness(stats, context.configuration.grid.bdsGrid);
+ double iqMeanGain = kEvGainTarget * knumHistogramBins / iqMean;
+ /*
+ * Estimate the gain needed to achieve a relative luminance target. To
+ * account for non-linearity caused by saturation, the value needs to be
+ * estimated in an iterative process, as multiplying by a gain will not
+ * increase the relative luminance by the same factor if some image
+ * regions are saturated.
+ */
double yGain = 1.0;
double yTarget = kRelativeLuminanceTarget;
- /*
- * Do this calculation a few times as brightness increase can be
- * non-linear when there are saturated regions.
- */
for (unsigned int i = 0; i < 8; i++) {
double yValue = estimateLuminance(context.frameContext,
context.configuration.grid.bdsGrid,
@@ -331,7 +336,7 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
break;
}
- computeExposure(context.frameContext, yGain);
+ computeExposure(context.frameContext, yGain, iqMeanGain);
frameCount_++;
}
@@ -31,10 +31,11 @@ public:
void process(IPAContext &context, const ipu3_uapi_stats_3a *stats) override;
private:
- void measureBrightness(const ipu3_uapi_stats_3a *stats,
- const ipu3_uapi_grid_config &grid);
+ double measureBrightness(const ipu3_uapi_stats_3a *stats,
+ const ipu3_uapi_grid_config &grid) const;
void filterExposure();
- void computeExposure(IPAFrameContext &frameContext, double yGain);
+ void computeExposure(IPAFrameContext &frameContext, double yGain,
+ double iqMeanGain);
double estimateLuminance(IPAFrameContext &frameContext,
const ipu3_uapi_grid_config &grid,
const ipu3_uapi_stats_3a *stats,
@@ -42,8 +43,6 @@ private:
uint64_t frameCount_;
- double iqMean_;
-
utils::Duration lineDuration_;
utils::Duration minShutterSpeed_;
utils::Duration maxShutterSpeed_;