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-rw-r--r--src/ipa/ipu3/algorithms/agc.cpp44
1 files changed, 22 insertions, 22 deletions
diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index 43a39ffd..9cd2ded5 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -62,12 +62,12 @@ static constexpr double kEvGainTarget = 0.5;
static constexpr uint32_t kNumStartupFrames = 10;
/*
- * Normalized luma value target.
+ * Relative luminance target.
*
* It's a number that's chosen so that, when the camera points at a grey
* target, the resulting image brightness is considered right.
*/
-static constexpr double kNormalizedLumaTarget = 0.16;
+static constexpr double kRelativeLuminanceTarget = 0.16;
Agc::Agc()
: frameCount_(0), iqMean_(0.0), lineDuration_(0s), minShutterSpeed_(0s),
@@ -250,12 +250,12 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
}
/**
- * \brief Estimate the average brightness of the frame
+ * \brief Estimate the relative luminance of the frame with a given gain
* \param[in] frameContext The shared IPA frame context
* \param[in] grid The grid used to store the statistics in the IPU3
* \param[in] stats The IPU3 statistics and ISP results
* \param[in] currentYGain The gain calculated on the current brightness level
- * \return The normalized luma
+ * \return The relative luminance
*
* Luma is the weighted sum of gamma-compressed R′G′B′ components of a color
* video. The luma values are normalized as 0.0 to 1.0, with 1.0 being a
@@ -263,12 +263,12 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double currentYGain)
* luma here.
*
* More detailed information can be found in:
- * https://en.wikipedia.org/wiki/Luma_(video)
+ * https://en.wikipedia.org/wiki/Relative_luminance
*/
-double Agc::computeInitialY(IPAFrameContext &frameContext,
- const ipu3_uapi_grid_config &grid,
- const ipu3_uapi_stats_3a *stats,
- double currentYGain)
+double Agc::estimateLuminance(IPAFrameContext &frameContext,
+ const ipu3_uapi_grid_config &grid,
+ const ipu3_uapi_stats_3a *stats,
+ double currentYGain)
{
double redSum = 0, greenSum = 0, blueSum = 0;
@@ -288,14 +288,14 @@ double Agc::computeInitialY(IPAFrameContext &frameContext,
}
/*
- * Estimate the sum of the brightness values, weighted with the gains
- * applied on the channels in AWB as the Rec. 601 luma.
+ * Apply the AWB gains to approximate colours correctly, use the Rec.
+ * 601 formula to calculate the relative luminance, and normalize it.
*/
- double Y_sum = redSum * frameContext.awb.gains.red * .299 +
- greenSum * frameContext.awb.gains.green * .587 +
- blueSum * frameContext.awb.gains.blue * .114;
+ double ySum = redSum * frameContext.awb.gains.red * 0.299
+ + greenSum * frameContext.awb.gains.green * 0.587
+ + blueSum * frameContext.awb.gains.blue * 0.114;
- return Y_sum / (grid.height * grid.width) / 255;
+ return ySum / (grid.height * grid.width) / 255;
}
/**
@@ -311,22 +311,22 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
measureBrightness(stats, context.configuration.grid.bdsGrid);
double currentYGain = 1.0;
- double targetY = kNormalizedLumaTarget;
+ double yTarget = kRelativeLuminanceTarget;
/*
* Do this calculation a few times as brightness increase can be
* non-linear when there are saturated regions.
*/
- for (int i = 0; i < 8; i++) {
- double initialY = computeInitialY(context.frameContext,
+ for (unsigned int i = 0; i < 8; i++) {
+ double yValue = estimateLuminance(context.frameContext,
context.configuration.grid.bdsGrid,
stats, currentYGain);
- double extra_gain = std::min(10.0, targetY / (initialY + .001));
+ double extra_gain = std::min(10.0, yTarget / (yValue + .001));
currentYGain *= extra_gain;
- LOG(IPU3Agc, Debug) << "Initial Y " << initialY
- << " target " << targetY
- << " gives gain " << currentYGain;
+ LOG(IPU3Agc, Debug) << "Y value: " << yValue
+ << ", Y target: " << yTarget
+ << ", gives gain " << currentYGain;
if (extra_gain < 1.01)
break;
}