[libcamera-devel] [PATCH 1/1] libcamera: controls: Add DigitalGain control

Tue Nov 24 11:15:25 CET 2020

Hi Jacopo

You're right, there's a relationship there. ColourGains obviously
gives you the red and blue gains determined by the AWB usually. You
might get the values 1.6 and 2.0 (for red and blue)

In our case, if we report a single "global gain" value you can kind of
imagine it as the green gain, where the colour gains were normalised
for a green gain of 1. So if the global gain was 1.25, then the actual
RGB gains used in my example would be 1.25 * (1.6, 1.0, 2.0)  = (2.0,
1.25, 2.5).

In the per-channel case I guess you'd be reporting these 3 numbers
directly. For me this duplicates information that's already in the
ColourGains, and it seems to muddle things up a bit. Imagine you had a
pipeline that lets you set a global gain - you'd have to query the
current white balance and work out all three numbers and set them. But
then you've set the white balance as well. Or maybe we do something
special so that you haven't? You see why it confuses me! So on balance
I'm with the single value approach, though I could live either way.

Thanks!
David

On Tue, 24 Nov 2020 at 08:43, Jacopo Mondi <jacopo at jmondi.org> wrote:
>
> Hi David,
>
> On Tue, Nov 24, 2020 at 08:28:09AM +0000, David Plowman wrote:
> > Hi everyone
> >
> > Sounds like we're happy enough from the point of view of this thing
> > being read-only (for Raspberry Pi at least). Would anyone want any
> > changes to the wording? Perhaps the final sentence/paragraph might now
> > be better as
> >
> > "This control is present in a request's ControlList only if the
> > pipeline supports setting the value. Even when it cannot be set by an
> > application, the pipeline may still report the actual value used in
> > the metadata returned with completed requests."
>
> I don't think it it necessary. It is implied that if a pipeline
> handler does not support changing the digital gain it should not
> expose it a one of the Camera's controls.
>
> Likewise, if it is something that applications should be informed of,
> it will be reported via metadata.
>
> I think we're good to go, except for the point that we've left
> floating about having this a single value or a per-channel value.
>
> I'm trying to get a feeling how this would be reported by your ISP. I
> see in example you have two per-channel values for the ColourGains
> control. Is this anyway related ?
>
> >
> > Any other thoughts?
> >
> > Thanks
> > David
> >
> > On Mon, 23 Nov 2020 at 09:17, Kieran Bingham
> > <kieran.bingham at ideasonboard.com> wrote:
> > >
> > > Hi Jacopo,
> > >
> > > On 23/11/2020 08:58, Jacopo Mondi wrote:
> > > > Hi Kieran,
> > > >
> > > > On Mon, Nov 16, 2020 at 10:40:25AM +0000, Kieran Bingham wrote:
> > > >> Hi David,
> > > >>
> > > >> On 27/10/2020 14:12, David Plowman wrote:
> > > >>> This control reports the global digital gain applied by the pipeline
> > > >>> as a whole, after capturing a raw image from the sensor.
> > > >>>
> > > >>> Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> > > >>> ---
> > > >>>  src/libcamera/control_ids.yaml | 11 +++++++++++
> > > >>>  1 file changed, 11 insertions(+)
> > > >>>
> > > >>> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> > > >>> index c8874fa9..e6362c74 100644
> > > >>> --- a/src/libcamera/control_ids.yaml
> > > >>> +++ b/src/libcamera/control_ids.yaml
> > > >>> @@ -530,4 +530,15 @@ controls:
> > > >>>          This control is only present when the pipeline supports scaling. Its
> > > >>>          maximum valid value is given by the properties::ScalerCropMaximum
> > > >>>          property, and the two can be used to implement digital zoom.
> > > >>> +
> > > >>> +  - DigitalGain:
> > > >>> +      type: float
> > > >>> +      description: |
> > > >>> +        Global digital gain value applied to the image during all the
> > > >>> +        processing steps after capturing the image from the sensor. Any raw
> > > >>> +        images, therefore, will not include this gain, but the final images
> > > >>> +        output by the imaging pipeline as a whole will include it.
> > > >>> +
> > > >>> +        This control is intended to report the value used by the image
> > > >>> +        processing pipeline.
> > > >>
> > > >>
> > > >> If this is a per-stream thing anyway, I guess it will then be up to
> > > >> pipeline handlers to set this to the appropriate value for each stream
> > > >> when it completes. The fact that this value would not be applicable to a
> > > >> RAW stream makes me think it certainly should be a per-stream metadata
> > > >> style value.
> > > >>
> > > >>
> > > >> I'd hope this could be handled by a common helper in that instance so it
> > > >> doesn't get left out of some pipeline handlers, but included in some,
> > > >> and become inconsistent. Not yet sure how we can handle that, but that
> > > >> will be a core issue anyway.
> > > >>
> > > >>
> > > >> I wonder if we should mark this somehow as read-only, at least until we
> > > >> determine that someone needs to set it.
> > > >>
> > > >> We could introduce a control property between type: and description:
> > > >>   read-only: true
> > > >
> > > > Isn't a read-only control just a metadata ?
> > > >
> > > > Wouldn't it be enough for a pipeline that does not support changing
> > > > the control value from applications not reporting it in the list of
> > > > supported Camera's controls, but only report it as part of a completed
> > > > request's metadata ?
> > >
> > > Ah, yes of course - because if the control is not listed as supported it
> > > won't be there to set in the first place! I forgot about that.
> > >
> > > So - indeed, no requirement to mark anything as read-only. That will be
> > > implicit.
> > >
> > > --
> > > Kieran
> > >
> > >
> > > >
> > > > Thanks
> > > >   j
> > > >
> > > >>
> > > >>
> > > >> Otherwise, I see no objections currently. I think we're just waiting on
> > > >> top-level thoughts from Laurent. (And perhaps per-stream controls, but
> > > >> that brings it's own questions )
> > > >>
> > > >> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > > >>
> > > >>
> > > >>>  ...
> > > >>>
> > > >>
> > > >> --
> > > >> Regards
> > > >> --
> > > >> Kieran
> > > >> _______________________________________________
> > > >> libcamera-devel mailing list
> > > >> libcamera-devel at lists.libcamera.org
> > > >> https://lists.libcamera.org/listinfo/libcamera-devel
> > >
> > > --
> > > Regards
> > > --
> > > Kieran