Welcome to how video frames are made. Look up interlacing and you'll get a much better understanding of the issue. You will always have this issue with Interlaced cameras.
I had suspected that was the issue but at the same time I wasn't expecting it as I had done a quick search on cx115 interlaced and hadn't found much (in the top 20 searches) but a new search for interlaced cx115 found plenty :(
In reply to:
cd supplied with CX cameras contains PMB software which can take surprisingly good framegrabs (final image has resolution bigger than 1920x1080, i don't know how...)
I had installed that on my desktop computer but not on the laptop I use for video editing. I'll give it a try - thanks :)
i would like to know how PMB does it, anyone has an idea?
The software understands that a single frame 'grab' isn't really a 'complete' single frame due to interlacing, and 'builds' a complete single frame from the interlaced components (the frame prior to/after the actual 'grabbed' frame.)