hum, thanks for the hint nicolai. Playing with hue and gamma, I can get a picture that is "understandable", but it seems that a lot of experimentation that is still needed in order to get a "good" picture...

Stopping and restarting gstreamer (from gst-launch) each time one wants to try with a different value seems inefficient at best. Is there a way to change the pipeline values *while* gstreamer is running?