Brightness contrast and saturation adjustments

[aalex]

There are excellent GStreamer video elements for adjusting BrCoSa. We should definitely use it.

[sofian]

We could actually support filters from the frei0r library (which includes these settings). The only issue with it is that it runs on the CPU and we might want to run everything using shaders instead.

[aalex]

I have some GLSL shaders around: https://github.com/aalex/toonloop/blob/master/src/shaders/brcosa.glsl

[aalex]

I have some chroma keying shader, as well: https://github.com/aalex/toonloop/blob/1.3/toon/effects/chromakey.py#L31

[aalex]

Also, leavecolor and blur shaders: https://github.com/aalex/toonloop/tree/1.3/toon/effects

[aalex]

Actually, the videobalance GStreamer element should to the trick. I believe it can run on the GPU, using some shader, internally, when possible, and will fallback to the CPU if it's the only option. https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good-plugins/html/gst-plugins-good-plugins-videobalance.html