[libcamera-devel] [PATCH 07/12] ipa: ipu3: awb: Correct the relevant zones proportion

[Laurent Pinchart]

Hi Jean-Michel,

On Wed, Sep 29, 2021 at 02:32:00PM +0200, Jean-Michel Hautbois wrote:
> On 29/09/2021 14:15, Laurent Pinchart wrote:
> > On Thu, Sep 23, 2021 at 10:16:20AM +0200, Jean-Michel Hautbois wrote:
> >> The algorithm uses the statistics of a cell only if there is not too
> >> much saturated pixels in it. The grey world algorithm works fine when
> >> there are a limited number of outliers.
> >> Consider a valid zone to be at least 80% of unsaturated cells in it.
> >> This value could very well be configurable, and make the algorithm more
> >> or less tolerant.
> >>
> >> While at it, implement it in a configure() call as it will not change
> >> during execution, and cache the cellsPerZone values.
> >>
> >> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> >> ---
> >>  src/ipa/ipu3/algorithms/awb.cpp | 32 +++++++++++++++++++++++---------
> >>  src/ipa/ipu3/algorithms/awb.h   |  5 +++++
> >>  2 files changed, 28 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
> >> index 51a38d05..800d023c 100644
> >> --- a/src/ipa/ipu3/algorithms/awb.cpp
> >> +++ b/src/ipa/ipu3/algorithms/awb.cpp
> >> @@ -17,7 +17,6 @@ namespace ipa::ipu3::algorithms {
> >>  
> >>  LOG_DEFINE_CATEGORY(IPU3Awb)
> >>  
> >> -static constexpr uint32_t kMinZonesCounted = 16;
> >>  static constexpr uint32_t kMinGreenLevelInZone = 32;
> >>  
> >>  /**
> >> @@ -169,6 +168,24 @@ Awb::Awb()
> >>  
> >>  Awb::~Awb() = default;
> >>  
> >> +int Awb::configure(IPAContext &context,
> >> +		   [[maybe_unused]] const IPAConfigInfo &configInfo)
> >> +{
> >> +	const ipu3_uapi_grid_config &grid = context.configuration.grid.bdsGrid;
> >> +
> >> +	cellsPerZoneX_ = round(grid.width / static_cast<double>(kAwbStatsSizeX));
> > 
> > s/round/std::round/
> > 
> > as you're using cmath (with a small corresponding comment in the commit
> > message).
> 
> OK :-).
> 
> >> +	cellsPerZoneY_ = round(grid.height / static_cast<double>(kAwbStatsSizeY));
> >> +
> >> +	/*
> >> +	 * Configure the minimum proportion of cells counted within a zone
> >> +	 * for it to be relevant for the grey world algorithm.
> >> +	 * \todo This proportion could be configured.
> >> +	 */
> >> +	cellsPerZoneThreshold_ = (cellsPerZoneX_ * cellsPerZoneY_) * 80 / 100;
> > 
> > No need for parentheses.
> > 
> > The patch looks fine to me, so
> > 
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > 
> > This however led me to notice that if the grid width isn't a multiple of
> > 16, we'll ignore some of the cells. If the grid width is 79, for
> > instance, 15 cells will be ignored. Would it be worth fixing that ?
> 
> We could still do :
> cellsPerZoneX_ = std::round(stride_ / static_cast<double>(kAwbStatsSizeX));
> 
> But we haven't included stride yet :-)

I think the best solution for this issue may be a variable number of
cells per zone. The question still holds though, is this an issue that
needs to be addressed, or is it harmless in practice ?

> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  /**
> >>   * The function estimates the correlated color temperature using
> >>   * from RGB color space input.
> >> @@ -205,7 +222,7 @@ void Awb::generateZones(std::vector<RGB> &zones)
> >>  	for (unsigned int i = 0; i < kAwbStatsSizeX * kAwbStatsSizeY; i++) {
> >>  		RGB zone;
> >>  		double counted = awbStats_[i].counted;
> >> -		if (counted >= kMinZonesCounted) {
> >> +		if (counted >= cellsPerZoneThreshold_) {
> >>  			zone.G = awbStats_[i].sum.green / counted;
> >>  			if (zone.G >= kMinGreenLevelInZone) {
> >>  				zone.R = awbStats_[i].sum.red / counted;
> >> @@ -220,19 +237,16 @@ void Awb::generateZones(std::vector<RGB> &zones)
> >>  void Awb::generateAwbStats(const ipu3_uapi_stats_3a *stats,
> >>  			   const ipu3_uapi_grid_config &grid)
> >>  {
> >> -	uint32_t cellsPerZoneX = round(grid.width / static_cast<double>(kAwbStatsSizeX));
> >> -	uint32_t cellsPerZoneY = round(grid.height / static_cast<double>(kAwbStatsSizeY));
> >> -
> >>  	/*
> >>  	 * Generate a (kAwbStatsSizeX x kAwbStatsSizeY) array from the IPU3 grid which is
> >>  	 * (grid.width x grid.height).
> >>  	 */
> >> -	for (unsigned int cellY = 0; cellY < kAwbStatsSizeY * cellsPerZoneY; cellY++) {
> >> -		for (unsigned int cellX = 0; cellX < kAwbStatsSizeX * cellsPerZoneX; cellX++) {
> >> +	for (unsigned int cellY = 0; cellY < kAwbStatsSizeY * cellsPerZoneY_; cellY++) {
> >> +		for (unsigned int cellX = 0; cellX < kAwbStatsSizeX * cellsPerZoneX_; cellX++) {
> >>  			uint32_t cellPosition = (cellY * grid.width + cellX)
> >>  					      * sizeof(Ipu3AwbCell);
> >> -			uint32_t zoneX = cellX / cellsPerZoneX;
> >> -			uint32_t zoneY = cellY / cellsPerZoneY;
> >> +			uint32_t zoneX = cellX / cellsPerZoneX_;
> >> +			uint32_t zoneY = cellY / cellsPerZoneY_;
> >>  
> >>  			uint32_t awbZonePosition = zoneY * kAwbStatsSizeX + zoneX;
> >>  
> >> diff --git a/src/ipa/ipu3/algorithms/awb.h b/src/ipa/ipu3/algorithms/awb.h
> >> index 3385ebe7..681d8c2b 100644
> >> --- a/src/ipa/ipu3/algorithms/awb.h
> >> +++ b/src/ipa/ipu3/algorithms/awb.h
> >> @@ -48,6 +48,7 @@ public:
> >>  	Awb();
> >>  	~Awb();
> >>  
> >> +	int configure(IPAContext &context, const IPAConfigInfo &configInfo) override;
> >>  	void prepare(IPAContext &context, ipu3_uapi_params *params) override;
> >>  	void process(IPAContext &context, const ipu3_uapi_stats_3a *stats) override;
> >>  
> >> @@ -85,6 +86,10 @@ private:
> >>  	std::vector<RGB> zones_;
> >>  	Accumulator awbStats_[kAwbStatsSizeX * kAwbStatsSizeY];
> >>  	AwbStatus asyncResults_;
> >> +
> >> +	uint32_t cellsPerZoneX_;
> >> +	uint32_t cellsPerZoneY_;
> >> +	uint32_t cellsPerZoneThreshold_;
> >>  };
> >>  
> >>  } /* namespace ipa::ipu3::algorithms */

-- 
Regards,

Laurent Pinchart