[PATCH v4 1/6] libcamera: controls: Update the ColourTemperature control to be writable

Laurent Pinchart laurent.pinchart at ideasonboard.com
Sat Aug 31 17:16:10 CEST 2024 

On Fri, Aug 30, 2024 at 04:31:50PM +0100, David Plowman wrote:
> On Fri, 30 Aug 2024 at 12:21, Stefan Klug wrote:
> > On Fri, Aug 30, 2024 at 01:15:55PM +0300, Laurent Pinchart wrote:
> > > On Fri, Aug 30, 2024 at 07:58:31AM +0200, Stefan Klug wrote:
> > > > On Fri, Aug 30, 2024 at 02:01:19AM +0300, Laurent Pinchart wrote:
> > > > > On Tue, Aug 13, 2024 at 10:44:18AM +0200, Stefan Klug wrote:
> > > > > > For manual control it is helpful to be able to specify a fixed colour
> > > > > > temperature. It also provides an easy way to apply the temperature
> > > > > > specific CCMs and colour gains that are contained in the tuning files.
> > > > > >
> > > > > > Document this and update the control dependencies.
> > > > > >
> > > > > > Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> > > > > > ---
> > > > > >  src/libcamera/control_ids_core.yaml | 24 ++++++++++++++++++++----
> > > > > >  1 file changed, 20 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/src/libcamera/control_ids_core.yaml b/src/libcamera/control_ids_core.yaml
> > > > > > index cf40771d3896..04dcc4af67fc 100644
> > > > > > --- a/src/libcamera/control_ids_core.yaml
> > > > > > +++ b/src/libcamera/control_ids_core.yaml
> > > > > > @@ -252,9 +252,12 @@ controls:
> > > > > >    - AwbEnable:
> > > > > >        type: bool
> > > > > >        description: |
> > > > > > -        Enable or disable the AWB.
> > > > > > +        Enable or disable the AWB. Disabling AWB stops updates to the
> > > > > > +        ColourGains and to the ColourCorrectionMatrix.
> > > > >
> > > > > Please split this in two paragraphs. The first paragraph is translated
> > > > > to a \brief doxygen command, and should be a single sentence. Same
> > > > > below.
> > > > >
> > > > > I would like to clarify this a bit. Here's an attempt, is it what you
> > > > > mean ?
> > > > >
> > > > >   Enable or disable the AWB.
> > > > >
> > > > >   When AWB is enabled, the algorithm estimates the colour temperature of
> > > > >   the scene, and computes colour gains and the colour correction matrix
> > > > >   automatically. The computed colour temperate, gains and correction
> > > > >   matrix are reported in metadata. The corresponding controls are ignored
> > > > >   if set in a request.
> > > > >
> > > > >   When AWB is disabled, the colour temperature, gains and correction
> > > > >   matrix are not updated automatically and can be set manually in
> > > > >   requests.
> > > >
> > > > Looks good, I'll apply that.
> > > >
> > > > > >
> > > > > > +        \sa ColourCorrectionMatrix
> > > > > >          \sa ColourGains
> > > > > > +        \sa ColourTemperature
> > > > > >
> > > > > >    # AwbMode needs further attention:
> > > > > >    # - Auto-generate max enum value.
> > > > > > @@ -309,13 +312,24 @@ controls:
> > > > > >          disabled.
> > > > > >
> > > > > >          \sa AwbEnable
> > > > > > +        \sa ColourTemperature
> > > > > >        size: [2]
> > > > > >
> > > > > >    - ColourTemperature:
> > > > > >        type: int32_t
> > > > > > -      description: Report the current estimate of the colour temperature, in
> > > > > > -        kelvin, for this frame. The ColourTemperature control can only be
> > > > > > -        returned in metadata.
> > > > > > +      description: |
> > > > > > +        Report the current estimate of the colour temperature, in kelvin, for
> > > > > > +        this frame. An implementation may also allow this control to be set when
> > > > >
> > > > > s/also //
> > > > >
> > > > > > +        AWB is disabled. In that case ColourGains and the ColourCorrectionMatrix
> > > > > > +        get set accordingly. If either ColourGains or ColourCorrectionMatrix are
> > > > > > +        specified at the same time, they take precedence.
> > > > >
> > > > > maybe "they take precedence, and the ColourTemperature is ignored" ? Or,
> > > > > if an application sets ColourTemperature and ColourGains but not
> > > > > ColourCorrectionMatrix, do you expect the implementation to apply the
> > > > > requested ColourGains and set ColourCorrectionMatrix based on the
> > > > > temperature ?
> > > >
> > > > The latter is exactly what happens. The following table lists the
> > > > possible options:
> > > >
> > > > CT -> CG(CT), CCM(CT)
> > > > CT, CG -> CG, CCM(CT)
> > > > CT, CCM -> CG(CT), CCM
> > > > CT, CG, CCM -> CG, CCM
> > >
> > > David, is this the behaviour you would also expect for Raspberry Pi ?
> 
> I'm guessing the question here is really what to do if an application
> sets both CT and CG together? The other cases seem fairly
> uncontroversial (?).

As far as I understand, for the rkisp1, the colour gains and the CCM are
both calculated based on the colour temperature. The case where the
application sets CT and CG is conceptually as problematic as the case
where it sets CT and CCM. Stefan, is that correct ?

> For us, I'm not sure it really makes much sense to supply both CT and
> CG at once. When someone sets CG, the algorithm estimates the CT and
> passes this to other algorithms, like lens shading and CCM. (So we
> actually have a "CG -> CG, CT(CG), CCM(CT)" kind of case going on.)

When an application sets CG, does the algorithm estimate CT from the
stats, or from the CG alone for RPi ? Stefan, how about your plans for
rkisp1 ?

> When I add this new control, it will calculate CG from the calibrated
> colour temperature curve in the camera tuning and use those, and pass
> the CT to those other algorithms (so like the first row in the table).

That's the main use, and I think we all agree on the behaviour. It seems
quite uncontroversial.

> I don't think I particularly want to implement cases where it takes a
> CG value, uses them, and also a random CT which it then passes on?
> Possibly I'd rather leave these cases (where we have both CT and CG on
> the LHS) as either "implementation dependent" or just "undefined", and
> recommend setting one or other.

I dislike implementation-dependent behaviours if we can avoid them, at
least in cases that we consider valid use cases. Is there a valid use
case for setting CT along with CG or CCM ? It sounds to me like there
wouldn't be one for RPi. Stefan, how about you ?

> Does that help or just confuse further?

Let's see how the discussion progresses :-) Thank you for your input.

> > > > Do you have a nice sentence for that?
> > >
> > > /me checks... I have a set of French proverbs, but none of the seem very
> > > appropriate. Sorry :-)
> >
> > What about "If ColourGains and ColourTemperature are specified at the
> > same time, ColourGains takes precedence. The same applies to
> > ColourCorrectionMatrix."?
> >
> > We can discuss the final wording after feedback from David.
> >
> > > > > > +
> > > > > > +        The metadata will only report measured colour temperature values when
> > > > > > +        available, even if set manually.
> > > > >
> > > > > I'm not sure to understand this.
> > > >
> > > > This is based on the comment from Kieran:
> > > > https://patchwork.libcamera.org/patch/20771/#30590 He wanted to prepare
> > > > for cases (RPi) where no temperature gets estimated. Only measurements
> > > > are returned in metadata. Manually set temperature is not reflected in
> > > > the metadata. This has the nice side effect, that you can set
> > > > AwbEnable=false, and still get temperature estimations in the metadata.
> > >
> > > This means that whether or not the estimated colour temperature will be
> > > returned in metadata will be platform-dependent. Can we avoid that ? It
> > > makes writing portable applications much more difficult.
> > >
> > > My other concern is that metadata is supposed to report the setting
> > > applied to a frame. The general rule is that, if a control can be set,
> > > the value that has been set for a frame is reported in metadata. There
> > > are exception for trigger-like controls. As this example clearly shows,
> > > having multiple controls that ultimately set the same values is also
> > > problematic from this point of view. Do we need to set a rule that
> > > higher-level controls that get translated to lower-level controls are
> > > never reported in metadata ?
> > >
> > > If we do that, then we'll have ColourTemperature as a control being
> > > defined differently from ColourTemperature as metadata. I'm not sure I
> > > like it much. Should we have two different controls ?
> >
> > We could split that to "MeasuredColourTemperature" and
> > "AppliedColorTemperature". But there are always cases where one of them
> > (or both) is not available (as discussed on Patch 3). I think on rkisp
> > we could ensure that MeasuredColourTemperature is always available and
> > contains "something" as the statistics are always available. But in the
> > end as a user I'd prefer to know when the algorithm failed to deduce a
> > valid colour temperature.

If the algorithm failed to estimate the colour temperature, that should
be indicated by the absence of an estimated colour temperature in
metadata.

David, why do you (if I understand correctly) stop estimating the colour
temperature from the statistics in manual AWB mode ?

> > > > > > +
> > > > > > +        \sa AwbEnable
> > > > > > +        \sa ColourCorrectionMatrix
> > > > > > +        \sa ColourGains
> > > > > >
> > > > > >    - Saturation:
> > > > > >        type: float
> > > > > > @@ -365,6 +379,8 @@ controls:
> > > > > >          transformation. The 3x3 matrix is stored in conventional reading
> > > > > >          order in an array of 9 floating point values.
> > > > > >
> > > > > > +        \sa AwbEnable
> > > > > > +        \sa ColourTemperature
> > > > > >        size: [3,3]
> > > > > >
> > > > > >    - ScalerCrop:

-- 
Regards,

Laurent Pinchart

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