From UVC jpeg webcam to OpenCV using Gstreamer

[philippe renon]

See https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-bad-plugins/html/gst-plugins-bad-plugins-plugin-opencv.html 

    Le Jeudi 6 avril 2017 18h21, philippe renon <philippe_renon at yahoo.fr> a écrit :
 

 Note that that gstreamer has a number of OpenCV elements that could do what you are after or be adapted to do it.
 

    Le Mardi 4 avril 2017 18h46, Damien Picard <picard.damien at gmail.com> a écrit :
 

 Thank you !
2017-04-03 20:49 GMT+02:00 Thiago Sousa Santos <thiagossantos at gmail.com>:



On Mon, Apr 3, 2017 at 11:14 AM, Damien Picard <picard.damien at gmail.com> wrote:

Hi,

Due to an issue in opencv4tegra, I can not capture from my UVC webcam using OpenCV. To get round this problem, I'm trying to use GStreamer and its Python bindings to capture jpeg images from the webcam.

To do that, I adapt this tutorial with a custom pipeline.
Currently my pipeline looks like this :

v4l2src ! image/jpeg,width=1920,height=1 080 ! jpegdec ! videoconvert ! appsink name=sink caps=video/x-raw, format=(string){BGR, GRAY8}; video/x-bayer,format=(string){ rggb,bggr,grbg,gbrg}

(The function that convert gstreamer to opencv array is exactly the same as in the tutorial)

It works (maybe the colors are not the good ones, but I'm not sure), but I'm wondering if there is a way to retrieve the jpeg images directly from gstreamer ? By this way, I will decode them using OpenCV and I hope that it could, at least, limits processing.


Not sure if decoding inside opencv or in gstreamer itself makes any difference but yes you can have gstreamer pass the jpeg images to you.

If you pay attention to your pipeline, it contains the 'jpegdec' element that is the one decoding jpegs into a raw format that later gets sent to appsink and into your application. So, you should just remove jpegdec and videoconvert and you will have jpeg images delivered directly to appsink. Remember to also remove the caps restrictions from appsink so it can accept jpeg input. Something like:

v4l2src ! image/jpeg,width=1920,height=1 080 ! appsink name=sink

Hope this helps,
 


Thank you in advance.

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Damien Picard
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Thiago Sousa Santos
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Damien Picard
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