I have a video, and I want to have an image (a part of the video, one framepiece) of the video. Making a screenshot of the part of the video is not a good idea, since it results in quality loss. So how can I download that part of a frame as an image?

Add the video to the project bin and select it, in the clip monitor move the playhead to the frame you want to extract and then right-click anywhere in the clip monitor and select Extract Frame or Extract Frame to Project. The former saves the frame as an image file anywhere you like, the latter saves the frame as an image clip in your project bin.

Hope this helps ...