[libcamera-devel] [PATCH 03/13] ipa: ipu3: awb: Use saturation under 90%

[Laurent Pinchart]

On Thu, Oct 14, 2021 at 11:32:37AM +0100, Kieran Bingham wrote:
> Quoting Jean-Michel Hautbois (2021-10-13 16:41:15)
> > The AWB grey world algorithm tries to find a grey value and it can't do
> > it on over-exposed images. To exclude those, the saturation ratio is
> > used for each cell, and the cell is included only if this ratio is 0.
> > 
> > Now that we have changed the threshold, more cells may be considered as
> > partially saturated and excluded, making the algorithm to not run.
> 
> ", preventing the algorithm from running efficiently." ?
> 
> or s/efficiently/correctly/ ?
> 
> > Change that behaviour, and consider 90% as a good enough ratio.
> > 
> > Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> > ---
> >  src/ipa/ipu3/algorithms/awb.cpp | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
> > index 5574bd44..30693923 100644
> > --- a/src/ipa/ipu3/algorithms/awb.cpp
> > +++ b/src/ipa/ipu3/algorithms/awb.cpp
> > @@ -161,6 +161,7 @@ int Awb::configure(IPAContext &context,
> >          * \todo This proportion could be configured.
> >          */
> >         cellsPerZoneThreshold_ = cellsPerZoneX_ * cellsPerZoneY_ * 80 / 100;
> > +       LOG(IPU3Awb, Debug) << "Threshold for AWB is set to " << cellsPerZoneThreshold_;
> 
> This is now a bit confusing. Your commit message mentions 90%, but the
> cellsPerZoneThreshold is 80%?
> 
> I guess these are two different thresholds...

To be considered, a zone needs 80% of the cells below a 90% saturation
ratio.

I'd add constexpr constants to these values.

> >         return 0;
> >  }
> > @@ -232,7 +233,7 @@ void Awb::generateAwbStats(const ipu3_uapi_stats_3a *stats)
> >                                 reinterpret_cast<const ipu3_uapi_awb_set_item *>(
> >                                         &stats->awb_raw_buffer.meta_data[cellPosition]
> >                                 );
> 
> This probably now deserves a comment explaining why 90% is used.
> 
> 			  /*
> 			   * Use cells which have less than 90%
> 			   * saturation as an initial means to include
> 			   * otherwise bright cells which are not fully
> 			   * saturated.
> 			   *
> 			   * \todo The 90% saturation rate may require
> 			   * further empirical measurements and
> 			   * optimisation during camera tuning phases.
> 			   */
> 
> > -                       if (currentCell->sat_ratio == 0) {
> > +                       if (currentCell->sat_ratio <= 255 * 90 / 100) {
> >                                 /* The cell is not saturated, use the current cell */
> >                                 awbStats_[awbZonePosition].counted++;
> >                                 uint32_t greenValue = currentCell->Gr_avg + currentCell->Gb_avg;

-- 
Regards,

Laurent Pinchart