[libcamera-devel] [PATCH v5 1/3] libcamera: controls: Add frame duration control
Jacopo Mondi
jacopo at jmondi.org
Thu Dec 10 17:04:15 CET 2020
Hi Naush,
On Thu, Dec 10, 2020 at 03:17:49PM +0000, Naushir Patuck wrote:
> Hi Jacopo,
>
> Thank you for your review comments.
>
> On Thu, 10 Dec 2020 at 14:48, Jacopo Mondi <jacopo at jmondi.org> wrote:
>
> > Hi Naush,
> > thanks for the update
> >
> > On Thu, Dec 10, 2020 at 01:34:24PM +0000, Naushir Patuck wrote:
> > > Add a float array control (controls::FrameDurations) to specify the
> > > minimum and maximum (in that order) frame duration to be used by the
> > > camera sensor.
> > >
> > > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > > Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> > > Tested-by: David Plowman <david.plowman at raspberrypi.com>
> > > ---
> > > src/libcamera/control_ids.yaml | 15 +++++++++++++++
> > > 1 file changed, 15 insertions(+)
> > >
> > > diff --git a/src/libcamera/control_ids.yaml
> > b/src/libcamera/control_ids.yaml
> > > index 6d6f0fee..7f1f8624 100644
> > > --- a/src/libcamera/control_ids.yaml
> > > +++ b/src/libcamera/control_ids.yaml
> > > @@ -554,4 +554,19 @@ controls:
> > > detection, additional format conversions etc) count as an
> > additional
> > > pipeline stage.
> >
> > So, I've gone through the lentghy discussions on v2 and v3.
> >
> > To be very honest, I think we still have some missing pieces and the
> > one that concerns me the more is the interaction of this control with
> > the selected AE mode and the consequences on exposure/shutter-time
> > priorites. I see all controls about Exposure have their interaction
> > definition defferred to a \todo item. This is of course not the ideal
> > situation but adding one make the issue only slightly worse. Deferring
> > these to the pipeline model definition might be an option.
> >
>
> You are entirely correct here on all ponts. There is a tightly coupled
> interaction with this FrameDurations control and interaction with the AGC
> algorithm. You have also thrown a spanner in the works for my plan :)
> David and I have been working on exactly this and we think we have
> addressed all these interactions. I have a set of patches that are ready
> to be pushed as a "phase 2", but wanted to get this through first so as not
> to muddy the waters too much. This set of "phase 2" patches address the
> following:
Ah great :)
>
> 1) Set VBLANK ahead of any other controls. This avoids the problem of
> setting EXPOSURE and having v4l2 reject the value due to stale limits.
> 2) Limit VBLANK (and hence frame duration) to what the sensor mode can
> actually support. This forms part of your Clipping discussion below.
> 3) Add an interaction with AE when FrameDurations. This addresses your
> concerns above, with AE knowing exactly what limits of shutter speed are
> achievable and working around any limitations based on exposure modes
> selected.
These are all improvements to the RPi implementation which are
certainly positive, but if I got these right, it's mostly about
implementation.
Using your point 3) as example, my main concern is more where/how
to specify how pipelines behaves (in the control documentation, in the
pipeline handler model etc), or if we want all pipelines to behave the
same, which I'm not even sure it's possible or desirable to enforce.
Did I get you right and your IPA will:
1) Select the appropriate exposure time using the hint provided by
AeExposureMode
2) Clip the selected interval in the FrameDurations limits
This seems more than reasonable but then the first question I have is
how to make this consistent for application among different
platforms/IPA implementations and how to clearly document that.
This additional controls does not define that, and I think it's fair.
What we should avoid is going in a direction that makes it too hard to
backtrack, and I don't think there's anything that bad here.
We just need more IPAs, to have a large enough base to prove these
concepts against a different implementation I guess.
>
> Perhaps I should make those changes as part of this series so you get the
> full picture right now?
The risk is to delay this more. I would do that on top if I got you
right and these are mostly improvements specific to the RPi
implementation.
>
>
> >
> > I'm willing to ack this patch, but I think there are a few details I
> > would like to discuss:
> >
> > - Clipping. We need a (per-configuration, like the ScalerCrop
> > rectangle) property to provide application limits and refer to it in
> > this control description. I'll address this on top, but I would
> > apreciate a:
> >
> > \todo Refer to the frame duration limits property to describe how
> > application-provided values gets clipped or how to reset the control
> > value to its default.
> >
>
> This is partially addressed in my point (2) above. However, I did not add
> a property, rather just did clipping based on VBLANK limits to the IPA. So
> do you think we should have a "properties::SensorMaxFramerate" or similar
> that provides the application the maximum possible framerate for this mode
> (derived from VBLANK control limits)? As mentioned above, right now I
> simply clip the user request to what the sensor mode can achieve.
As an implementation it's fine, but I think we need a mechanism to allow
application to access that information. At least, I know we need this
for Android, so something has to be added.
And I think once we have that property is fair to mention here that
values outside the limits there reported will be clipped (and that's
something I think we can assume for all pipelines).
Then if you want to support this, you will simply have to update the
Camera property to report the VBLANK limits.
>
>
> >
> > - This is both a control and a metadata. I think the
> > description is only about 'setting' the FrameDurations, not reading
> > it. We have discussed in length the former but somewhat ignored the
> > latter.
> >
> > The 'reading' case could addressed by introducing a read-only control
> > (ie FrameDuration) only to be used as metadata. But this might even be
> > more confusing as people will wonder why they have to use
> > 'Duration-s-' when they want a precise value and theres a 'Duration'
> > (without 's') available. I'll propose an additional section but if
> > you have ideas please suggest them. Also, feel free to leave this
> > last part out if it turns out to be controversial and would delay the
> > series any longer.
> >
>
> Yes, good point here. Returning a "FrameDuration" may be a bit redundant,
> as this information is conveyed in the FrameBuffer timestamps. What do
> other folks think?
That's a good point. We have timestamps and durations can be
calculated. I still think it would be nicer for application to
have a direct way to access this as part of the Request metadata. Or
we can expose the sensor timestamp from the Request and let them calculate
durations..
>
>
> >
> > >
> > > + - FrameDurations:
> > > + type: float
> >
> > I understand this is meant to accommodate standard FPS like 29,97 FPS
> > (-.-) but won't expressing this as nanoseconds with a uin64_t
> > representation be capable of achieving the same. Floating point
> > arithmentic is generally a bit harder and clunky to handle when doing
> > calculations. I won't push if you think a float is better.
> >
>
> I only used float here as that is what we use in our IPA :) Happy to change
> to int64_t based numbers.
>
I would slightly prefer, but it's a gut feeling. I suspect you have a
reasons why you used float in your IPA I am missing. If that's the
case feel free to keep float here.
> >
> > > + description: |
> >
> > I would:
> > size: [2]
> > description:
> > The minimum and maximum (in that order) frame duration,
> > expressed in micro-seconds.
> >
> > When provided by applications the control specifies the
> > sensor frame duration interval the pipeline has to use. This
> > could also limit the largest exposure times the sensor can
> > use. For example, if a maximum frame duration of 33ms is
> > requested (corresponding to 30 frames per second), the
> > sensor will not be able to raise the exposure time above
> > 33ms. A fixed frame duration is achieved by setting the
> > minimum and maximum values to be the same.
> >
> > \todo Refer to the frame duration limits property to describe how
> > application-provided values gets clipped or how to reset the
> > control
> > values to their defaults.
> >
> > \todo Better specify how the frame durations interact with the
> > exposure control algorithm.
> > \sa AeEnable
> > \sa AeExposureMode
> > \sa ExposureTime
> >
> > -----------------8< you can cut here 8<--------------------
> >
> > When reported by pipelines the control expresses the duration
> > of the sensor frame used to produce streams part of the completed
> > Request. The minimum and maximum values shall then be the same,
> > as the
> > sensor frame duration is a fixed parameter. The sensor frame
> > duration is one of the parameter that defines the capture
> > frame rate but it does not alone provide enough information
> > to fully calculate it as it does not account for pipeline
> > processing delays.
> >
> > \todo Define how to calculate the capture frame rate by
> > defining controls to report additional delays introduced by
> > the capture pipeline or post-processing stages (ie JPEG
> > conversion, frame scaling).
> >
>
> Sure, no problem. I will use the above wording and perhaps expand a bit
> more on the AE interactions.
Great thanks, we can hopefully ack this sooner than later then.
Thanks
j
>
>
> >
> > > + Specifies the minimum and maximum (in that order) allowable
> > frame
> > > + duration, in micro-seconds, for the sensor to use. This could
> > also limit
> > > + the largest exposure times the sensor can use. For example, if
> > a maximum
> > > + frame duration of 33ms is requested (corresponding to 30 frames
> > per
> > > + second), the sensor will not be able raise the exposure time
> > above 33ms.
> >
> > s/will not be able raise/will not be able to raise/
> > Fixed in the above suggestions.
> >
>
> Ack.
>
> Regards,
> Naush
>
>
> >
> > Thanks
> > j
>
>
> > > + A fixed frame duration is achieved by setting the minimum and
> > maximum
> > > + values to be the same. Note that the sensor may not always be
> > able to
> > > + provide the requested frame duration limits depending on its
> > mode
> > > + configuration.
> >
> > > + \sa ExposureTime
> > > + size: [2]
> > > ...
> > > --
> > > 2.25.1
> > >
> > > _______________________________________________
> > > libcamera-devel mailing list
> > > libcamera-devel at lists.libcamera.org
> > > https://lists.libcamera.org/listinfo/libcamera-devel
> >
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