[libcamera-devel] Camera mode selection

[David Plowman]

Hi Kieran

Thanks for the reply. Let me try and clarify one or two of those points!

On Mon, 25 Jan 2021 at 12:39, Kieran Bingham
<kieran.bingham at ideasonboard.com> wrote:
>
> Hi David,
>
> On 22/01/2021 14:29, David Plowman wrote:
> > Hi everyone
> >
> > I was wondering if I might return to the topic of camera mode
> > selection. (Apologies if this might turn into another long
> > meta-discussion!)
> >
> > We already know that there are questions as to how and when you might
> > trade off things like better resolution versus higher framerates, and
> > it's not clear how an application might signal what it wants.
> >
> > Another case I've found myself faced with recently is how to select
> > camera modes jointly, such as when doing preview and then capture.
> > Typically the preview will ask for a smaller resolution, and capture a
> > larger one. You might adjust the preview to have the same aspect ratio
> > as the capture. But so far as I understand it, it's difficult to
> > guarantee that the preview mode will have the same field of view as
> > the capture.
>
> Are you considering this use case as configuring one stream as preview,
> running, and then reconfiguring for capture? or as two stream
> configurations?

Yes, I'm treating the two separately. So firstly I'd configure the
stream for preview, probably with the same aspect ratio as the
eventual capture, but with significantly lower resolution. The idea is
of course to get reasonable framerates for preview (and make the
system work less hard).

For capture, the camera has to be stopped and reconfigured for the big
capture resolution.

>
>
> > Do others see this as a problem, and if so how might one fix it? Have
> > more in the way of flags that "hint" at what the application wants?
> > Perhaps pass in a second resolution with the rule that the mode
> > selected for the first resolution must have the save FoV as the
> > second?
>
> Is this where the 'Raw' stream would be configured, but without
> providing buffers to control what the FoV defined at the sensor actually
> is ?

Well, maybe. I understand with the preview that I could request a raw
stream, leave it at the full resolution, and not pass any buffers.
But, correct me if I'm wrong, I'd end up in full resolution mode, with
slow framerates and so forth - is that right?

I suppose I could try halving the raw dimensions on the assumption
that there's a 2x2 binned mode. But that's not always guaranteed...
what would happen then?

>
> > I often find myself coming back to the idea of selecting modes
> > explicitly - applications frequently know what sensor they're dealing
> > with, and probably know exactly which modes they want too.
>
> To clarify, for a 'mode' do you mean a fixed setting of (Sensor)
> width/height/framerate? or something more?

I suppose I mean fixed width, height, field of view (i.e. binning and
cropping within the sensor), and (maximum) framerate.

Thanks!

David

> --
> Kieran
>
>
>
> >
> > Anyway, I'd be interested to hear people's thoughts on this one!
> >
> > Thanks and best regards
> > David
> > _______________________________________________
> > libcamera-devel mailing list
> > libcamera-devel at lists.libcamera.org
> > https://lists.libcamera.org/listinfo/libcamera-devel
> >
>
> --
> Regards
> --
> Kieran