[PATCH v3] ipa: libipa: Change constraint Y target to piecewise linear function

[Kieran Bingham]

Quoting Paul Elder (2024-06-10 15:22:04)
> On Mon, Jun 10, 2024 at 11:31:32AM +0100, Kieran Bingham wrote:
> > Quoting Paul Elder (2024-06-07 08:59:14)
> > > Change the constraint luminance target from a scalar value to a
> > > piecewise linear function that needs to be sampled by the estimated lux
> > > value.
> > > 
> > > Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> > > 
> > > ---
> > > This patch depends on v5 of "ipa:: Move Pwl from Raspberry Pi"
> > > 
> > > Changes in v3:
> > > - use new PointF that's a typedef of Vector
> > > 
> > > Changes in v2:
> > > - s/FPoint/PointF/
> > > - construct default Pwl with *two* points so that it actually constructs
> > >   properly
> > > ---
> > >  src/ipa/libipa/agc_mean_luminance.cpp | 15 +++++++++------
> > >  src/ipa/libipa/agc_mean_luminance.h   |  4 ++--
> > >  2 files changed, 11 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/src/ipa/libipa/agc_mean_luminance.cpp b/src/ipa/libipa/agc_mean_luminance.cpp
> > > index 10c16850d..575143610 100644
> > > --- a/src/ipa/libipa/agc_mean_luminance.cpp
> > > +++ b/src/ipa/libipa/agc_mean_luminance.cpp
> > > @@ -168,8 +168,10 @@ void AgcMeanLuminance::parseConstraint(const YamlObject &modeDict, int32_t id)
> > >                 AgcConstraint::Bound bound = static_cast<AgcConstraint::Bound>(idx);
> > >                 double qLo = content["qLo"].get<double>().value_or(0.98);
> > >                 double qHi = content["qHi"].get<double>().value_or(1.0);
> > > -               double yTarget =
> > > -                       content["yTarget"].getList<double>().value_or(std::vector<double>{ 0.5 }).at(0);
> > > +               Pwl yTarget;
> > > +               int ret = yTarget.readYaml(content["yTarget"]);
> > > +               if (ret < 0)
> > > +                       yTarget = Pwl({ Pwl::PointF({ 0, 0.5 }), Pwl::PointF({ 1000, 0.5 }) });
> > >  
> > >                 AgcConstraint constraint = { bound, qLo, qHi, yTarget };
> > >  
> > > @@ -221,7 +223,7 @@ int AgcMeanLuminance::parseConstraintModes(const YamlObject &tuningData)
> > >                         AgcConstraint::Bound::lower,
> > >                         0.98,
> > >                         1.0,
> > > -                       0.5
> > > +                       Pwl({ Pwl::PointF({ 0, 0.5 }), Pwl::PointF({ 1000, 0.5 }) })
> > 
> > In V2, I asked:
> > 
> > > Should this be some pre-constructed global const if it's going to be
> > > used in multiple places?
> >     
> > And you replied:
> > 
> > Probably? It's used three times; twice here and once more for
> > relativeLuminance.
> > 
> > But I don't see that action taken for v3?
> 
> It's split between two patches and I don't really want to introduce
> another depencency at this stage...

So - what action can we take to earn the RB tag?

Pwl::PointF({ 0, 0.5 }), Pwl::PointF({ 1000, 0.5 }) is opaque,
underdocumented, and used in multiple places.

Not documenting the meaning behind "0, 0.5"->"1000, 0.5" is currently
blocking me giving a tag...


Furthermore I see "ipa: libipa: agc: Change luminance target to
piecewise linear function" does this:


+	std::vector<Pwl::PointF> points = { Pwl::PointF({     0, kDefaultRelativeLuminanceTarget }),
+					    Pwl::PointF({ 10000, kDefaultRelativeLuminanceTarget }) };

which is suddenly 0->10000.

Is that the one you mean ?

kDefaultRelativeLuminanceTarget is set to 0.16; ? So they're not the
same. Why aren't they the same? Should they be?



--
Kieran


> 
> 
> Paul
> 
> > 
> > If you do so, it would be a good opportunity to define and document the
> > value choices for 0,0.5 -> 1000,0.5 and state clearly that this is a
> > single horizontal linear default Pwl used to express a mid-point
> > brightness level regardless of the input colour temperature?
> > 
> > 
> > 
> > 
> > >                 };
> > >  
> > >                 constraintModes_[controls::ConstraintNormal].insert(
> > > @@ -471,16 +473,17 @@ double AgcMeanLuminance::estimateInitialGain(double lux) const
> > >   * \param[in] constraintModeIndex The index of the constraint to adhere to
> > >   * \param[in] hist A histogram over which to calculate inter-quantile means
> > >   * \param[in] gain The gain to clamp
> > > + * \param[in] lux The lux value at which to sample the constraint luminance target pwl
> > >   *
> > >   * \return The gain clamped within the constraint bounds
> > >   */
> > >  double AgcMeanLuminance::constraintClampGain(uint32_t constraintModeIndex,
> > >                                              const Histogram &hist,
> > > -                                            double gain)
> > > +                                            double gain, double lux)
> > >  {
> > >         std::vector<AgcConstraint> &constraints = constraintModes_[constraintModeIndex];
> > >         for (const AgcConstraint &constraint : constraints) {
> > > -               double newGain = constraint.yTarget * hist.bins() /
> > > +               double newGain = constraint.yTarget.eval(constraint.yTarget.domain().clamp(lux)) * hist.bins() /
> > >                                  hist.interQuantileMean(constraint.qLo, constraint.qHi);
> > >  
> > >                 if (constraint.bound == AgcConstraint::Bound::lower &&
> > > @@ -559,7 +562,7 @@ AgcMeanLuminance::calculateNewEv(uint32_t constraintModeIndex,
> > >                 exposureModeHelpers_.at(exposureModeIndex);
> > >  
> > >         double gain = estimateInitialGain(lux);
> > > -       gain = constraintClampGain(constraintModeIndex, yHist, gain);
> > > +       gain = constraintClampGain(constraintModeIndex, yHist, gain, lux);
> > >  
> > >         /*
> > >          * We don't check whether we're already close to the target, because
> > > diff --git a/src/ipa/libipa/agc_mean_luminance.h b/src/ipa/libipa/agc_mean_luminance.h
> > > index 6ec2a0dc9..d43f673dd 100644
> > > --- a/src/ipa/libipa/agc_mean_luminance.h
> > > +++ b/src/ipa/libipa/agc_mean_luminance.h
> > > @@ -38,7 +38,7 @@ public:
> > >                 Bound bound;
> > >                 double qLo;
> > >                 double qHi;
> > > -               double yTarget;
> > > +               Pwl yTarget;
> > >         };
> > >  
> > >         int parseTuningData(const YamlObject &tuningData);
> > > @@ -80,7 +80,7 @@ private:
> > >         double estimateInitialGain(double lux) const;
> > >         double constraintClampGain(uint32_t constraintModeIndex,
> > >                                    const Histogram &hist,
> > > -                                  double gain);
> > > +                                  double gain, double lux);
> > >         utils::Duration filterExposure(utils::Duration exposureValue);
> > >  
> > >         uint64_t frameCount_;
> > > -- 
> > > 2.39.2
> > >