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ipa: ipu3: agc: Standardize vocabulary on "relative luminance"

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The AGC computes the average relative luminance of the frame and calls
the value "normalized luma", "brightness" or "initialY". The latter is
the most accurate term, as the relative luminance is abbreviated Y, but
the "initial" prefix isn't accurate.

Standardize the vocabulary on "relative luminance" in code and comments,
abbreviating it to Y when needed.

While at it, rename variables to match the libcamera coding style.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Laurent Pinchart 2021-11-16 16:29:23 +02:00
parent 65628512df
commit 8d9b39f8ad
2 changed files with 26 additions and 26 deletions
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44
src/ipa/ipu3/algorithms/agc.cpp
View file

@ -62,12 +62,12 @@ static constexpr double kEvGainTarget = 0.5;
static constexpr uint32_t kNumStartupFrames = 10; 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 * It's a number that's chosen so that, when the camera points at a grey
* target, the resulting image brightness is considered right. * target, the resulting image brightness is considered right.
*/ */
static constexpr double kNormalizedLumaTarget = 0.16; static constexpr double kRelativeLuminanceTarget = 0.16;
Agc::Agc() Agc::Agc()
: frameCount_(0), iqMean_(0.0), lineDuration_(0s), minShutterSpeed_(0s), : 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] frameContext The shared IPA frame context
* \param[in] grid The grid used to store the statistics in the IPU3 * \param[in] grid The grid used to store the statistics in the IPU3
* \param[in] stats The IPU3 statistics and ISP results * \param[in] stats The IPU3 statistics and ISP results
* \param[in] currentYGain The gain calculated on the current brightness level * \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 * 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 * 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. * luma here.
* *
* More detailed information can be found in: * 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, double Agc::estimateLuminance(IPAFrameContext &frameContext,
const ipu3_uapi_grid_config &grid, const ipu3_uapi_grid_config &grid,
const ipu3_uapi_stats_3a *stats, const ipu3_uapi_stats_3a *stats,
double currentYGain) double currentYGain)
{ {
double redSum = 0, greenSum = 0, blueSum = 0; 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 * Apply the AWB gains to approximate colours correctly, use the Rec.
* applied on the channels in AWB as the Rec. 601 luma. * 601 formula to calculate the relative luminance, and normalize it.
*/ */
double Y_sum = redSum * frameContext.awb.gains.red * .299 + double ySum = redSum * frameContext.awb.gains.red * 0.299
greenSum * frameContext.awb.gains.green * .587 + + greenSum * frameContext.awb.gains.green * 0.587
blueSum * frameContext.awb.gains.blue * .114; + 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); measureBrightness(stats, context.configuration.grid.bdsGrid);
double currentYGain = 1.0; double currentYGain = 1.0;
double targetY = kNormalizedLumaTarget; double yTarget = kRelativeLuminanceTarget;
/* /*
* Do this calculation a few times as brightness increase can be * Do this calculation a few times as brightness increase can be
* non-linear when there are saturated regions. * non-linear when there are saturated regions.
*/ */
for (int i = 0; i < 8; i++) { for (unsigned int i = 0; i < 8; i++) {
double initialY = computeInitialY(context.frameContext, double yValue = estimateLuminance(context.frameContext,
context.configuration.grid.bdsGrid, context.configuration.grid.bdsGrid,
stats, currentYGain); 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; currentYGain *= extra_gain;
LOG(IPU3Agc, Debug) << "Initial Y " << initialY LOG(IPU3Agc, Debug) << "Y value: " << yValue
<< " target " << targetY << ", Y target: " << yTarget
<< " gives gain " << currentYGain; << ", gives gain " << currentYGain;
if (extra_gain < 1.01) if (extra_gain < 1.01)
break; break;
} }

8
src/ipa/ipu3/algorithms/agc.h
View file

@ -35,10 +35,10 @@ private:
const ipu3_uapi_grid_config &grid); const ipu3_uapi_grid_config &grid);
void filterExposure(); void filterExposure();
void computeExposure(IPAFrameContext &frameContext, double currentYGain); void computeExposure(IPAFrameContext &frameContext, double currentYGain);
double computeInitialY(IPAFrameContext &frameContext, double estimateLuminance(IPAFrameContext &frameContext,
const ipu3_uapi_grid_config &grid, const ipu3_uapi_grid_config &grid,
const ipu3_uapi_stats_3a *stats, const ipu3_uapi_stats_3a *stats,
double currentYGain); double currentYGain);
uint64_t frameCount_; uint64_t frameCount_;