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

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Date:   Fri, 28 Oct 2016 19:56:47 -0700
From:   Matt Ranostay <matt@...ostay.consulting>
To:     Marek Vasut <marex@...x.de>
Cc:     Devin Heitmueller <dheitmueller@...nellabs.com>,
        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 Fri, Oct 28, 2016 at 1:40 PM, Marek Vasut <marex@...x.de> wrote:
> 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.

Yes this is only 64 pixel (8x8 grid) but it is video still. Does have
some major pluses over a FLIR camera though, mainly power usage is
really low, and cost is lower (although that reason is decreasing
everyday).

>
> --
> Best regards,
> Marek Vasut