plugin writing: base class for format conversion

[Michael Gruner]

Glad it worked!

If you want to overlay a picture (like the thermal bar in that GIF), you can check the gdkpixbufoverlay <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good/html/gst-plugins-good-plugins-gdkpixbufoverlay.html> element. If you also want to add a border to the image so that the overlay doesn’t cover part of the image, you may look at the videobox <https://gstreamer.freedesktop.org/documentation/videobox/index.html?gi-language=c> element. By setting the “right” property to a negative value, you’ll add a black border to the right of the image.

> On 18 Jul 2021, at 05:09, Guennadi Liakhovetski <g.liakhovetski at gmx.de> wrote:
> 
> On Sat, 17 Jul 2021, Michael Gruner wrote:
> 
>> The default is to only allow the same format. You need to reimplement
>> the transform_caps virtual method in order to change the format. (note
>> that transform_caps is a basetransform method).
> 
> Great, this works! Thanks very much! I've got a colour-coded image now.
> Ideally - if not too much work - I'd also like to get numeric temperature
> information like on the side bar in the GIF on
> https://github.com/makerportal/raspi-thermal-cam or maybe in an additional
> in-frame metadata channel. I found a discussion here
> https://developer.ridgerun.com/wiki/index.php/GStreamer_and_in-band_metadata
> but that doesn't seem to have made it to the mainline. I guess the most
> user-friendly would be adding a side bar like in the former link. It
> should be possible to extend the width of the image and overlay that kind
> of information, right?
> 
> Thanks
> Guennadi
> 
>>> On 17 Jul 2021, at 13:50, Guennadi Liakhovetski <g.liakhovetski at gmx.de> wrote:
>>> 
>>> 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
>>>>> _______________________________________________
>>>>> gstreamer-devel mailing list
>>>>> gstreamer-devel at lists.freedesktop.org
>>>>> https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>>>> 
>> 

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