Re: Potential integration of thermal cameras into v4l

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hello,

On Tue, Jan 10, 2023 at 12:45:18PM +0100, Jacopo Mondi via libcamera-devel wrote:
> On Tue, Jan 10, 2023 at 10:46:26AM +0200, Pekka Paalanen wrote:
> > On Sat, 7 Jan 2023 22:58:41 +0100 Sophie Friedrich wrote:
> >
> > > Hello people,
> > >
> > > over the past months I've written a driver for the Guide MobIR Air¹
> > > USB-C thermal camera. The driver uses v4l2loopback and runs in user
> > > space with python.² The driver manages camera state, calibration and
> > > conversion of the raw microbolometer to temperature values.
> > >
> > > In my research I couldn't find any mentions of a thermal camera support
> > > in the Linux kernel nor the media subsystem, so I assume I'm the first
> > > to ask here and we would presumably need lay out some ground work.
> > >
> > > The current camera driver outputs the temperature in the Y16 format as
> > > Kelvin * 100 (i.e. 28056 (raw) -> 280.56K -> 7.41°C). This allows for
> > > further processing down the line with i.e. OpenCV, but has its
> > > limitations. Especially as temps of only up to 382.2°C can be displayed
> > > currently.
> > >
> > > Does it seem feasible to integrate support for thermal cameras in the
> > > Linux kernel and more specifically in the v4l2 subsystem?
> >
> > Hi,
> >
> > since no-one else replied to you yet, I thought to mention my 2c
> > (I don't really do camera stuff myself so far):
> >
> > Perhaps the best place is to reach out to the libcamera community:
> > https://libcamera.org/
> 
> cc-ed the libcamera list
> 
> I agree it would be interesting to better understand what you mean by
> driver here.
> 
> The camera seems to be a UVC camera, does it deliver frames with the
> current UVC driver or do you need kernel patches to support it ?

From a quick glance at the github project linked below, it doesn't seem
to be a UVC camera.

Sophie, could you please share the `lsusb -v` output for the device (you
can limit it to a specific device with `-d VID:PID`), running as root
(e.g. with `sudo`) if possible ?

> I would also be interested why it needs to go through v4l2loopback..
> 
> > It sounds to me like you want to do some hardware-specific
> > processing in userspace, and it might not be great to try to come
> > up with a generic thermal camera API at the kernel UAPI level.
> > That's where libcamera fits in.
> >
> > As for the pixel type, maybe use a floating-point type to avoid
> > range/precision problems? E.g. DRM_FORMAT_R32F for application
> > facing API. That format does not seem to exist yet, but it's
> > trivial to add into kernel's drm_fourcc.h and should be well
> > accepted IMO.
> >
> > > [1]: https://www.guideir.com/products/mobileaccessories/mobirair/data_300.html
> > > [2]: https://github.com/tyalie/pyMobirAir-v4l2/
> 
> This link is broken :)

Works for me.

-- 
Regards,

Laurent Pinchart