plugin writing: base class for format conversion

[Guennadi Liakhovetski]

Hi Michael,

On Sat, 17 Jul 2021, Michael Gruner wrote:

> Hi Guennadi
>
> The videoconvert element can already handle this conversion for you:
>
> gst-launch-1.0 v4l2src ! videoconvert ! video/x-raw,format=RGB ! …

Yes, I know about videoconvert, but I need to do some special processing
of thermal data. For the algorithms to work I have to access the raw data,
which is output by the v4l2 driver in GRAY16_BE format (1-to-1 from the
camera), and I want to transform that to a colour gradient similar to well
known thermal images, so my plugin cannot just stay within GRAY16_BE and
use videoconvert to convert that to RGB - you'd just get a gray image of
course.

> If you, for other reason, need to write your own element, you probably
> want to use the videofilter base class. It’s a specialization of the
> basetransform class for video. The important virtual method for you to
> implement is “transform_caps”, that will allow you to specify the input
> and output caps respectively.

The videofilter class is "allowed" to convert between formats? I thought
it would be, so I actually tried it. But I was unable to get it to input
and output different formats. I was only able to get it to work with the
same format. Are you sure that is supposed to work?

Thanks
Guennadi

> Michael
>
> > On 17 Jul 2021, at 05:05, Guennadi Liakhovetski via gstreamer-devel <gstreamer-devel at lists.freedesktop.org> wrote:
> >
> > Hi,
> >
> > I'm trying to write a plugin to convert data from a thermal camera. It
> > should take data from the v4l2src source in GRAY16_BE format and convert
> > it to an RGB video output. I'm looking at gst-element-maker but I'm not
> > finding any suitable base class that would take video/x-raw as input and
> > generate the same as output and would convert between format. Do I have to
> > write a plugin from scratch? Or should I use basetransform? Any tutorials
> > for that?
> >
> > Thanks
> > Guennadi
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>