development direction of OpenCV elements

[David Rothlisberger]

On 26 November 2014 at 13:58, hubbup <hubbup at gmail.com> wrote:
> There are OpenCV elements in the bad plugin.
> I want to know the development direction of the OpenCV elements.

I'm not a GStreamer developer and I don't speak for the project, but my
own experience with the OpenCV elements is that they are at best a proof
of concept. (As are many of the high-level operations in OpenCV itself,
but that's a tangent -- I only hope that the guy from the automated
missile guidance company who was posting questions on this list a few
weeks ago about OpenCV face recognition wasn't serious.) :-/

Anyway image processing in practice (in my experience) needs gluing
together so many different operations that writing a separate GStreamer
element for each operation would be way too much effort -- what I ended
up doing is ending my GStreamer pipeline with an `appsink`, grabbing
frames from that, doing the image processing in python code, and feeding
it into an `appsrc` in another GStreamer pipeline.

> 1. Should an element contain only one OpenCV function?
>     (I think cvdilate and cverode can be merged and
>                 cvsobel and cvlaplace can be merged)

That raises an interesting question about the backward compatibility
guarantees of plugins in "bad". Can you just remove an element
altogether? I don't know.

> 2. Do we have any plan to support OpenCV 2.x or OpenCv 3.x?
>     (OpenCV 2.X recommends to use "Mat" format rather than "Iplimage".)

Presumably the "Mat" API is C++ rather than C. Presumably it's possible
to write a GStreamer plugin in C++, but even if the GStreamer OpenCV
plugin does have a maintainer, they may not be willing to test &
maintain such a change on all platforms.

If you were going to put the effort into this I'd suggest something more
ambitious whereby you have a single element and the actual OpenCV
operation is configurable via properties. But getting the caps right
depending on what properties you set might be difficult. Oh well.

Dave.