linux-kernel - Re: [RFC] v4l2 support for thermopile devices

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Date:   Fri, 28 Oct 2016 22:40:44 +0200
From:   Marek Vasut <marex@...x.de>
To:     Devin Heitmueller <dheitmueller@...nellabs.com>,
        Matt Ranostay <matt@...ostay.consulting>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Attila Kinali <attila@...ali.ch>
Subject: Re: [RFC] v4l2 support for thermopile devices

On 10/28/2016 10:30 PM, Devin Heitmueller wrote:
> Hi Matt,
> 
>> Need some input for the video pixel data types, which the device we
>> are using (see datasheet links below) is outputting pixel data in
>> little endian 16-bit of which a 12-bits signed value is used.  Does it
>> make sense to do some basic processing on the data since greyscale is
>> going to look weird with temperatures under 0C degrees? Namely a cold
>> object is going to be brighter than the hottest object it could read.
>> Or should a new V4L2_PIX_FMT_* be defined and processing done in
>> software?  Another issue is how to report the scaling value of 0.25 C
>> for each LSB of the pixels to the respecting recording application.
> 
> Regarding the format for the pixel data:  I did some research into
> this when doing some driver work for the Seek Thermal (a product
> similar to the FLIR Lepton).  While it would be nice to be able to use
> an existing application like VLC or gStreamer to just take the video
> and capture from the V4L2 interface with no additional userland code,
> the reality is that how you colorize the data is going to be highly
> user specific (e.g. what thermal ranges to show with what colors,
> etc).  If your goal is really to do a V4L2 driver which returns the
> raw data, then you're probably best returning it in the native
> greyscale format (whether that be an existing V4L2 PIX_FMT or a new
> one needs to be defined), and then in software you can figure out how
> to colorize it.

All true, I also did my share of poking into SEEK Thermal USB and it is
an excellent candidate for a V4L2 driver, that one. But I think this
device here is producing much smaller images, something like 8x8 pixels.

-- 
Best regards,
Marek Vasut