Frei0r perspective filter usage

[Jos van Riswick]

Thnx! these were the eye openers I was looking for :)

I updated gstreamer and found the wonky use of capitals and lowercase
x-es and Y-s with gst-inspect-1.0 and it works ! Oh and you even
quoted the entire working chain haha I should read ahead next time :)

Ok I'll check out this standard perspective, but it doesn't seem to pop up:

gst-inspect-1.0 perspective
No such element or plugin 'perspective'


or you meant one has to turn this on manually when compiling?

Jos

On Thu, Feb 2, 2017 at 8:47 AM, Antonio Ospite <ao2 at ao2.it> wrote:

> On Wed, 1 Feb 2017 14:27:54 -0800 (PST)
> josvanr <josvanr at gmail.com> wrote:
>
> > Hello!
> >
>
> Hi,
>
> > I'm trying to de-perspective the images from my webcam with the frei0r
> > perspective filter. I'm trying this:
> >
> > gst-launch -v v4l2src device=/dev/webcam1
> > !  video/x-raw-yuv,width=1600,height=1200 !  ffmpegcolorspace
> > !  frei0r-filter-perspective, top-left-X=0, top-left-Y=0,
> > top-right-X=0.1, top-right-Y=0.1, bottom-left-X=0.2, bottom-left-Y=1,
> > bottom-right-X=0.8, bottom-right-Y=1 ! ffmpegcolorspace ! xvimagesink
> >
>
> Apart from the fact that you should really update to GStreamer 1.x,
> there are a couple of issues in the pipeline:
>
>  1. extra commas in the part referring to the frei0r-filter-perspective
>     element and its properties, remove them;
>
>  2. the X properties apparently need to be spelled with a lower case 'x'
>     (e.g. top-left-x instead of top-left-X and so on), not sure why this
>     is tho.
>
> > There are no error massages, but there doesn't seem to be any
> > perspectiving going on.
>
> gst-launch-1.0 does give errors, update if you can.
>
> > I'm not sure this is the way to invoke the filter. How do I find out
> > how to do that?
>
> gst-inspect-1.0 frei0r-filter-perspective
>
> > I can remember looking at the sources a couple of years ago and thats
> > how i came up with these parameters.  But not sure if this is
> > correct.....
>
> This pipeline seems to work here:
>
>   gst-launch-1.0 -v \
>     videotestsrc ! \
>     videoconvert ! \
>     frei0r-filter-perspective \
>       top-left-x=0 \
>       top-left-Y=0 \
>       top-right-x=0.1 \
>       top-right-Y=0.1 \
>       bottom-left-x=0.2 \
>       bottom-left-Y=1 \
>       bottom-right-x=0.8 \
>       bottom-right-Y=1 ! \
>     videoconvert ! \
>     autovideosink
>
> and BTW there is also a standard "perspective" element in GStreamer 1.x
> which accepts a "matrix" property, IIRC it can only be set via source
> code and not via gst-launch-1.0 but it's a more convenient form if you
> are reusing a perspective matrix created by some other means (e.g.
> OpenCV), check out "gst-inspect-1.0 perspective", and
> https://git.ao2.it/experiments/gstreamer.git/blob/HEAD:/c/gst-perspective-
> example/gst-perspective-example.c
>
> Ciao ciao,
>    Antonio
>
> --
> Antonio Ospite
> https://ao2.it
> https://twitter.com/ao2it
>
> A: Because it messes up the order in which people normally read text.
>    See http://en.wikipedia.org/wiki/Posting_style
> Q: Why is top-posting such a bad thing?
>
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