[libcamera-devel] [PATCH 11/12] ipa: ipu3: agc: Rewrite and simplify the brightness loop

[Kieran Bingham]

On Thu, Sep 23, 2021 at 10:16:24AM +0200, Jean-Michel Hautbois wrote:
> Now that we know how exactly the AWB statistics are formatted, use a
> simplified loop in processBrightness() to parse the green values and get the
> histogram.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 54 +++++++++++++--------------------
>  src/ipa/ipu3/algorithms/agc.h   |  2 ++
>  2 files changed, 23 insertions(+), 33 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 5ff50f4a..ebbc5676 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -6,6 +6,7 @@
>   */
>  
>  #include "agc.h"
> +#include "awb.h"
>  
>  #include <algorithm>
>  #include <chrono>
> @@ -47,9 +48,6 @@ static constexpr uint32_t kMaxExposure = 1976;
>  static constexpr uint32_t knumHistogramBins = 256;
>  static constexpr double kEvGainTarget = 0.5;
>  
> -/* A cell is 8 bytes and contains averages for RGB values and saturation ratio */
> -static constexpr uint8_t kCellSize = 8;
> -
>  Agc::Agc()
>  	: frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
>  	  maxExposureTime_(0s), prevExposure_(0s), prevExposureNoDg_(0s),
> @@ -60,6 +58,10 @@ Agc::Agc()
>  int Agc::configure([[maybe_unused]] IPAContext &context,

looks like context is no longer [[maybe_unused]].


>  		   const IPAConfigInfo &configInfo)
>  {
> +	const ipu3_uapi_grid_config &grid = context.configuration.grid.bdsGrid;
> +	/* The grid is aligned to the next multiple of 4 */
> +	stride_ = (grid.width + 3) / 4 * 4;

This is familiar...

How about putting a stride into context.configuration.grid.stride and
calculating it once during calculateBdsGrid()?

> +
>  	lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
>  		      / configInfo.sensorInfo.pixelRate;
>  	maxExposureTime_ = kMaxExposure * lineDuration_;
> @@ -70,37 +72,23 @@ int Agc::configure([[maybe_unused]] IPAContext &context,
>  void Agc::processBrightness(const ipu3_uapi_stats_3a *stats,
>  			    const ipu3_uapi_grid_config &grid)
>  {
> -	const struct ipu3_uapi_grid_config statsAeGrid = stats->stats_4a_config.awb_config.grid;
> -	Rectangle aeRegion = { statsAeGrid.x_start,
> -			       statsAeGrid.y_start,
> -			       static_cast<unsigned int>(statsAeGrid.x_end - statsAeGrid.x_start) + 1,
> -			       static_cast<unsigned int>(statsAeGrid.y_end - statsAeGrid.y_start) + 1 };
> -	Point topleft = aeRegion.topLeft();
> -	int topleftX = topleft.x >> grid.block_width_log2;
> -	int topleftY = topleft.y >> grid.block_height_log2;
> -
> -	/* Align to the grid cell width and height */
> -	uint32_t startX = topleftX << grid.block_width_log2;
> -	uint32_t startY = topleftY * grid.width << grid.block_width_log2;
> -	uint32_t endX = (startX + (aeRegion.size().width >> grid.block_width_log2)) << grid.block_width_log2;
> -	uint32_t i, j;
> -	uint32_t count = 0;
> -
>  	uint32_t hist[knumHistogramBins] = { 0 };
> -	for (j = topleftY;
> -	     j < topleftY + (aeRegion.size().height >> grid.block_height_log2);
> -	     j++) {
> -		for (i = startX + startY; i < endX + startY; i += kCellSize) {
> -			/*
> -			 * The grid width (and maybe height) is not reliable.
> -			 * We observed a bit shift which makes the value 160 to be 32 in the stats grid.
> -			 * Use the one passed at init time.
> -			 */
> -			if (stats->awb_raw_buffer.meta_data[i + 4 + j * grid.width] == 0) {
> -				uint8_t Gr = stats->awb_raw_buffer.meta_data[i + 0 + j * grid.width];
> -				uint8_t Gb = stats->awb_raw_buffer.meta_data[i + 3 + j * grid.width];
> -				hist[(Gr + Gb) / 2]++;
> -				count++;
> +
> +	for (unsigned int cellY = 0; cellY < grid.height; cellY++) {
> +		for (unsigned int cellX = 0; cellX < stride_; cellX++) {
> +			uint32_t cellPosition = cellY * stride_ + cellX
> +					      * sizeof(Ipu3AwbCell);
> +
> +			/* Cast the initial IPU3 structure to simplify the reading */
> +			const Ipu3AwbCell *cell =
> +				reinterpret_cast<const Ipu3AwbCell *>(
> +					&stats->awb_raw_buffer.meta_data[cellPosition]
> +				);
> +
> +			if (cell->satRatio == 0) {

Is the satRatio usage clear yet? Is it always 0? or do you see other
values here?

Should it be less than a saturation threshold? (perhaps not unless we
have a way to configure that anyway)


> +				uint8_t gr = cell->greenRedAvg;
> +				uint8_t gb = cell->greenBlueAvg;
> +				hist[(gr + gb) / 2]++;
>  			}
>  		}
>  	}
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index e36797d3..64b71c65 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -50,6 +50,8 @@ private:
>  	Duration prevExposureNoDg_;
>  	Duration currentExposure_;
>  	Duration currentExposureNoDg_;
> +
> +	uint32_t stride_;
>  };
>  
>  } /* namespace ipa::ipu3::algorithms */
> -- 
> 2.30.2
> 

--
Kieran