It is essential when attempting to monitor the QUALITY of images in FCP that you use an external NTSC VIDEO Monitor (or PAL, if that’s where you are).
Especially after you render…
the Canvas is never high-quality (by design) and should not be used to make determinations of image quality of clips or graphics.
VERY IMPORTANT:
If you position the graphics, make SURE the VERTICAL setting for each KEY-FRAME (start, stop or hold) is always a EVEN INTEGER. (examples: 4, not 3 / -144, not -143.27 / 336, not 335.62)
I sometimes forget to check this and I can end up with images that look fuzzy when in-position.
This info applies to re-positioning ANYTHING on the Timeline: moving video, freeze-frames, internally-generated titles, and imported graphics.
It can be quite detrimental to the quality of your final output to not double-check this every time you reposition and/or re-size an image.